commit 805efa3637c75ada04bb224265cf69629eb97452 Author: Lee Witek Date: Tue Dec 12 20:30:31 2017 +0000 diff --git a/zx81 rom listing b/zx81 rom listing new file mode 100644 index 0000000..5feacfd --- /dev/null +++ b/zx81 rom listing @@ -0,0 +1,10554 @@ +; =========================================================== +; An Assembly Listing of the Operating System of the ZX81 ROM +; =========================================================== +; ------------------------- +; Last updated: 13-DEC-2004 +; ------------------------- +; +; Work in progress. +; This file will cross-assemble an original version of the "Improved" +; ZX81 ROM. The file can be modified to change the behaviour of the ROM +; when used in emulators although there is no spare space available. +; +; The documentation is incomplete and if you can find a copy +; of "The Complete Spectrum ROM Disassembly" then many routines +; such as POINTERS and most of the mathematical routines are +; similar and often identical. +; +; I've used the labels from the above book in this file and also +; some from the more elusive Complete ZX81 ROM Disassembly +; by the same publishers, Melbourne House. + + +#define DEFB .BYTE ; TASM cross-assembler definitions +#define DEFW .WORD +#define EQU .EQU + + +;***************************************** +;** Part 1. RESTART ROUTINES AND TABLES ** +;***************************************** + +; ----------- +; THE 'START' +; ----------- +; All Z80 chips start at location zero. +; At start-up the Interrupt Mode is 0, ZX computers use Interrupt Mode 1. +; Interrupts are disabled . + +;; START +L0000: OUT ($FD),A ; Turn off the NMI generator if this ROM is + ; running in ZX81 hardware. This does nothing + ; if this ROM is running within an upgraded + ; ZX80. + LD BC,$7FFF ; Set BC to the top of possible RAM. + ; The higher unpopulated addresses are used for + ; video generation. + JP L03CB ; Jump forward to RAM-CHECK. + +; ------------------- +; THE 'ERROR' RESTART +; ------------------- +; The error restart deals immediately with an error. ZX computers execute the +; same code in runtime as when checking syntax. If the error occurred while +; running a program then a brief report is produced. If the error occurred +; while entering a BASIC line or in input etc., then the error marker indicates +; the exact point at which the error lies. + +;; ERROR-1 +L0008: LD HL,($4016) ; fetch character address from CH_ADD. + LD ($4018),HL ; and set the error pointer X_PTR. + JR L0056 ; forward to continue at ERROR-2. + +; ------------------------------- +; THE 'PRINT A CHARACTER' RESTART +; ------------------------------- +; This restart prints the character in the accumulator using the alternate +; register set so there is no requirement to save the main registers. +; There is sufficient room available to separate a space (zero) from other +; characters as leading spaces need not be considered with a space. + +;; PRINT-A +L0010: AND A ; test for zero - space. + JP NZ,L07F1 ; jump forward if not to PRINT-CH. + + JP L07F5 ; jump forward to PRINT-SP. + +; --- + + DEFB $FF ; unused location. + +; --------------------------------- +; THE 'COLLECT A CHARACTER' RESTART +; --------------------------------- +; The character addressed by the system variable CH_ADD is fetched and if it +; is a non-space, non-cursor character it is returned else CH_ADD is +; incremented and the new addressed character tested until it is not a space. + +;; GET-CHAR +L0018: LD HL,($4016) ; set HL to character address CH_ADD. + LD A,(HL) ; fetch addressed character to A. + +;; TEST-SP +L001C: AND A ; test for space. + RET NZ ; return if not a space + + NOP ; else trickle through + NOP ; to the next routine. + +; ------------------------------------ +; THE 'COLLECT NEXT CHARACTER' RESTART +; ------------------------------------ +; The character address in incremented and the new addressed character is +; returned if not a space, or cursor, else the process is repeated. + +;; NEXT-CHAR +L0020: CALL L0049 ; routine CH-ADD+1 gets next immediate + ; character. + JR L001C ; back to TEST-SP. + +; --- + + DEFB $FF, $FF, $FF ; unused locations. + +; --------------------------------------- +; THE 'FLOATING POINT CALCULATOR' RESTART +; --------------------------------------- +; this restart jumps to the recursive floating-point calculator. +; the ZX81's internal, FORTH-like, stack-based language. +; +; In the five remaining bytes there is, appropriately, enough room for the +; end-calc literal - the instruction which exits the calculator. + +;; FP-CALC +L0028: JP L199D ; jump immediately to the CALCULATE routine. + +; --- + +;; end-calc +L002B: POP AF ; drop the calculator return address RE-ENTRY + EXX ; switch to the other set. + + EX (SP),HL ; transfer H'L' to machine stack for the + ; return address. + ; when exiting recursion then the previous + ; pointer is transferred to H'L'. + + EXX ; back to main set. + RET ; return. + + +; ----------------------------- +; THE 'MAKE BC SPACES' RESTART +; ----------------------------- +; This restart is used eight times to create, in workspace, the number of +; spaces passed in the BC register. + +;; BC-SPACES +L0030: PUSH BC ; push number of spaces on stack. + LD HL,($4014) ; fetch edit line location from E_LINE. + PUSH HL ; save this value on stack. + JP L1488 ; jump forward to continue at RESERVE. + +; ----------------------- +; THE 'INTERRUPT' RESTART +; ----------------------- +; The Mode 1 Interrupt routine is concerned solely with generating the central +; television picture. +; On the ZX81 interrupts are enabled only during the interrupt routine, +; although the interrupt +; This Interrupt Service Routine automatically disables interrupts at the +; outset and the last interrupt in a cascade exits before the interrupts are +; enabled. +; There is no DI instruction in the ZX81 ROM. +; An maskable interrupt is triggered when bit 6 of the Z80's Refresh register +; changes from set to reset. +; The Z80 will always be executing a HALT (NEWLINE) when the interrupt occurs. +; A HALT instruction repeatedly executes NOPS but the seven lower bits +; of the Refresh register are incremented each time as they are when any +; simple instruction is executed. (The lower 7 bits are incremented twice for +; a prefixed instruction) +; This is controlled by the Sinclair Computer Logic Chip - manufactured from +; a Ferranti Uncommitted Logic Array. +; +; When a Mode 1 Interrupt occurs the Program Counter, which is the address in +; the upper echo display following the NEWLINE/HALT instruction, goes on the +; machine stack. 193 interrupts are required to generate the last part of +; the 56th border line and then the 192 lines of the central TV picture and, +; although each interrupt interrupts the previous one, there are no stack +; problems as the 'return address' is discarded each time. +; +; The scan line counter in C counts down from 8 to 1 within the generation of +; each text line. For the first interrupt in a cascade the initial value of +; C is set to 1 for the last border line. +; Timing is of the utmost importance as the RH border, horizontal retrace +; and LH border are mostly generated in the 58 clock cycles this routine +; takes . + +;; INTERRUPT +L0038: DEC C ; (4) decrement C - the scan line counter. + JP NZ,L0045 ; (10/10) JUMP forward if not zero to SCAN-LINE + + POP HL ; (10) point to start of next row in display + ; file. + + DEC B ; (4) decrement the row counter. (4) + RET Z ; (11/5) return when picture complete to L028B + ; with interrupts disabled. + + SET 3,C ; (8) Load the scan line counter with eight. + ; Note. LD C,$08 is 7 clock cycles which + ; is way too fast. + +; -> + +;; WAIT-INT +L0041: LD R,A ; (9) Load R with initial rising value $DD. + + EI ; (4) Enable Interrupts. [ R is now $DE ]. + + JP (HL) ; (4) jump to the echo display file in upper + ; memory and execute characters $00 - $3F + ; as NOP instructions. The video hardware + ; is able to read these characters and, + ; with the I register is able to convert + ; the character bitmaps in this ROM into a + ; line of bytes. Eventually the NEWLINE/HALT + ; will be encountered before R reaches $FF. + ; It is however the transition from $FF to + ; $80 that triggers the next interrupt. + ; [ The Refresh register is now $DF ] + +; --- + +;; SCAN-LINE +L0045: POP DE ; (10) discard the address after NEWLINE as the + ; same text line has to be done again + ; eight times. + + RET Z ; (5) Harmless Nonsensical Timing. + ; (condition never met) + + JR L0041 ; (12) back to WAIT-INT + +; Note. that a computer with less than 4K or RAM will have a collapsed +; display file and the above mechanism deals with both types of display. +; +; With a full display, the 32 characters in the line are treated as NOPS +; and the Refresh register rises from $E0 to $FF and, at the next instruction +; - HALT, the interrupt occurs. +; With a collapsed display and an initial NEWLINE/HALT, it is the NOPs +; generated by the HALT that cause the Refresh value to rise from $E0 to $FF, +; triggering an Interrupt on the next transition. +; This works happily for all display lines between these extremes and the +; generation of the 32 character, 1 pixel high, line will always take 128 +; clock cycles. + +; --------------------------------- +; THE 'INCREMENT CH-ADD' SUBROUTINE +; --------------------------------- +; This is the subroutine that increments the character address system variable +; and returns if it is not the cursor character. The ZX81 has an actual +; character at the cursor position rather than a pointer system variable +; as is the case with prior and subsequent ZX computers. + +;; CH-ADD+1 +L0049: LD HL,($4016) ; fetch character address to CH_ADD. + +;; TEMP-PTR1 +L004C: INC HL ; address next immediate location. + +;; TEMP-PTR2 +L004D: LD ($4016),HL ; update system variable CH_ADD. + + LD A,(HL) ; fetch the character. + CP $7F ; compare to cursor character. + RET NZ ; return if not the cursor. + + JR L004C ; back for next character to TEMP-PTR1. + +; -------------------- +; THE 'ERROR-2' BRANCH +; -------------------- +; This is a continuation of the error restart. +; If the error occurred in runtime then the error stack pointer will probably +; lead to an error report being printed unless it occurred during input. +; If the error occurred when checking syntax then the error stack pointer +; will be an editing routine and the position of the error will be shown +; when the lower screen is reprinted. + +;; ERROR-2 +L0056: POP HL ; pop the return address which points to the + ; DEFB, error code, after the RST 08. + LD L,(HL) ; load L with the error code. HL is not needed + ; anymore. + +;; ERROR-3 +L0058: LD (IY+$00),L ; place error code in system variable ERR_NR + LD SP,($4002) ; set the stack pointer from ERR_SP + CALL L0207 ; routine SLOW/FAST selects slow mode. + JP L14BC ; exit to address on stack via routine SET-MIN. + +; --- + + DEFB $FF ; unused. + +; ------------------------------------ +; THE 'NON MASKABLE INTERRUPT' ROUTINE +; ------------------------------------ +; Jim Westwood's technical dodge using Non-Maskable Interrupts solved the +; flicker problem of the ZX80 and gave the ZX81 a multi-tasking SLOW mode +; with a steady display. Note that the AF' register is reserved for this +; function and its interaction with the display routines. When counting +; TV lines, the NMI makes no use of the main registers. +; The circuitry for the NMI generator is contained within the SCL (Sinclair +; Computer Logic) chip. +; ( It takes 32 clock cycles while incrementing towards zero ). + +;; NMI +L0066: EX AF,AF' ; (4) switch in the NMI's copy of the + ; accumulator. + INC A ; (4) increment. + JP M,L006D ; (10/10) jump, if minus, to NMI-RET as this is + ; part of a test to see if the NMI + ; generation is working or an intermediate + ; value for the ascending negated blank + ; line counter. + + JR Z,L006F ; (12) forward to NMI-CONT + ; when line count has incremented to zero. + +; Note. the synchronizing NMI when A increments from zero to one takes this +; 7 clock cycle route making 39 clock cycles in all. + +;; NMI-RET +L006D: EX AF,AF' ; (4) switch out the incremented line counter + ; or test result $80 + RET ; (10) return to User application for a while. + +; --- + +; This branch is taken when the 55 (or 31) lines have been drawn. + +;; NMI-CONT +L006F: EX AF,AF' ; (4) restore the main accumulator. + + PUSH AF ; (11) * Save Main Registers + PUSH BC ; (11) ** + PUSH DE ; (11) *** + PUSH HL ; (11) **** + +; the next set-up procedure is only really applicable when the top set of +; blank lines have been generated. + + LD HL,($400C) ; (16) fetch start of Display File from D_FILE + ; points to the HALT at beginning. + SET 7,H ; (8) point to upper 32K 'echo display file' + + HALT ; (1) HALT synchronizes with NMI. + ; Used with special hardware connected to the + ; Z80 HALT and WAIT lines to take 1 clock cycle. + +; ---------------------------------------------------------------------------- +; the NMI has been generated - start counting. The cathode ray is at the RH +; side of the TV. +; First the NMI servicing, similar to CALL = 17 clock cycles. +; Then the time taken by the NMI for zero-to-one path = 39 cycles +; The HALT above = 01 cycles. +; The two instructions below = 19 cycles. +; The code at L0281 up to and including the CALL = 43 cycles. +; The Called routine at L02B5 = 24 cycles. +; -------------------------------------- --- +; Total Z80 instructions = 143 cycles. +; +; Meanwhile in TV world, +; Horizontal retrace = 15 cycles. +; Left blanking border 8 character positions = 32 cycles +; Generation of 75% scanline from the first NEWLINE = 96 cycles +; --------------------------------------- --- +; 143 cycles +; +; Since at the time the first JP (HL) is encountered to execute the echo +; display another 8 character positions have to be put out, then the +; Refresh register need to hold $F8. Working back and counteracting +; the fact that every instruction increments the Refresh register then +; the value that is loaded into R needs to be $F5. :-) +; +; + OUT ($FD),A ; (11) Stop the NMI generator. + + JP (IX) ; (8) forward to L0281 (after top) or L028F + +; **************** +; ** KEY TABLES ** +; **************** + +; ------------------------------- +; THE 'UNSHIFTED' CHARACTER CODES +; ------------------------------- + +;; K-UNSHIFT +L007E: DEFB $3F ; Z + DEFB $3D ; X + DEFB $28 ; C + DEFB $3B ; V + DEFB $26 ; A + DEFB $38 ; S + DEFB $29 ; D + DEFB $2B ; F + DEFB $2C ; G + DEFB $36 ; Q + DEFB $3C ; W + DEFB $2A ; E + DEFB $37 ; R + DEFB $39 ; T + DEFB $1D ; 1 + DEFB $1E ; 2 + DEFB $1F ; 3 + DEFB $20 ; 4 + DEFB $21 ; 5 + DEFB $1C ; 0 + DEFB $25 ; 9 + DEFB $24 ; 8 + DEFB $23 ; 7 + DEFB $22 ; 6 + DEFB $35 ; P + DEFB $34 ; O + DEFB $2E ; I + DEFB $3A ; U + DEFB $3E ; Y + DEFB $76 ; NEWLINE + DEFB $31 ; L + DEFB $30 ; K + DEFB $2F ; J + DEFB $2D ; H + DEFB $00 ; SPACE + DEFB $1B ; . + DEFB $32 ; M + DEFB $33 ; N + DEFB $27 ; B + +; ----------------------------- +; THE 'SHIFTED' CHARACTER CODES +; ----------------------------- + + +;; K-SHIFT +L00A5: DEFB $0E ; : + DEFB $19 ; ; + DEFB $0F ; ? + DEFB $18 ; / + DEFB $E3 ; STOP + DEFB $E1 ; LPRINT + DEFB $E4 ; SLOW + DEFB $E5 ; FAST + DEFB $E2 ; LLIST + DEFB $C0 ; "" + DEFB $D9 ; OR + DEFB $E0 ; STEP + DEFB $DB ; <= + DEFB $DD ; <> + DEFB $75 ; EDIT + DEFB $DA ; AND + DEFB $DE ; THEN + DEFB $DF ; TO + DEFB $72 ; cursor-left + DEFB $77 ; RUBOUT + DEFB $74 ; GRAPHICS + DEFB $73 ; cursor-right + DEFB $70 ; cursor-up + DEFB $71 ; cursor-down + DEFB $0B ; " + DEFB $11 ; ) + DEFB $10 ; ( + DEFB $0D ; $ + DEFB $DC ; >= + DEFB $79 ; FUNCTION + DEFB $14 ; = + DEFB $15 ; + + DEFB $16 ; - + DEFB $D8 ; ** + DEFB $0C ; £ + DEFB $1A ; , + DEFB $12 ; > + DEFB $13 ; < + DEFB $17 ; * + +; ------------------------------ +; THE 'FUNCTION' CHARACTER CODES +; ------------------------------ + + +;; K-FUNCT +L00CC: DEFB $CD ; LN + DEFB $CE ; EXP + DEFB $C1 ; AT + DEFB $78 ; KL + DEFB $CA ; ASN + DEFB $CB ; ACS + DEFB $CC ; ATN + DEFB $D1 ; SGN + DEFB $D2 ; ABS + DEFB $C7 ; SIN + DEFB $C8 ; COS + DEFB $C9 ; TAN + DEFB $CF ; INT + DEFB $40 ; RND + DEFB $78 ; KL + DEFB $78 ; KL + DEFB $78 ; KL + DEFB $78 ; KL + DEFB $78 ; KL + DEFB $78 ; KL + DEFB $78 ; KL + DEFB $78 ; KL + DEFB $78 ; KL + DEFB $78 ; KL + DEFB $C2 ; TAB + DEFB $D3 ; PEEK + DEFB $C4 ; CODE + DEFB $D6 ; CHR$ + DEFB $D5 ; STR$ + DEFB $78 ; KL + DEFB $D4 ; USR + DEFB $C6 ; LEN + DEFB $C5 ; VAL + DEFB $D0 ; SQR + DEFB $78 ; KL + DEFB $78 ; KL + DEFB $42 ; PI + DEFB $D7 ; NOT + DEFB $41 ; INKEY$ + +; ----------------------------- +; THE 'GRAPHIC' CHARACTER CODES +; ----------------------------- + + +;; K-GRAPH +L00F3: DEFB $08 ; graphic + DEFB $0A ; graphic + DEFB $09 ; graphic + DEFB $8A ; graphic + DEFB $89 ; graphic + DEFB $81 ; graphic + DEFB $82 ; graphic + DEFB $07 ; graphic + DEFB $84 ; graphic + DEFB $06 ; graphic + DEFB $01 ; graphic + DEFB $02 ; graphic + DEFB $87 ; graphic + DEFB $04 ; graphic + DEFB $05 ; graphic + DEFB $77 ; RUBOUT + DEFB $78 ; KL + DEFB $85 ; graphic + DEFB $03 ; graphic + DEFB $83 ; graphic + DEFB $8B ; graphic + DEFB $91 ; inverse ) + DEFB $90 ; inverse ( + DEFB $8D ; inverse $ + DEFB $86 ; graphic + DEFB $78 ; KL + DEFB $92 ; inverse > + DEFB $95 ; inverse + + DEFB $96 ; inverse - + DEFB $88 ; graphic + +; ------------------ +; THE 'TOKEN' TABLES +; ------------------ + + +;; TOKENS +L0111: DEFB $0F+$80 ; '?'+$80 + DEFB $0B,$0B+$80 ; "" + DEFB $26,$39+$80 ; AT + DEFB $39,$26,$27+$80 ; TAB + DEFB $0F+$80 ; '?'+$80 + DEFB $28,$34,$29,$2A+$80 ; CODE + DEFB $3B,$26,$31+$80 ; VAL + DEFB $31,$2A,$33+$80 ; LEN + DEFB $38,$2E,$33+$80 ; SIN + DEFB $28,$34,$38+$80 ; COS + DEFB $39,$26,$33+$80 ; TAN + DEFB $26,$38,$33+$80 ; ASN + DEFB $26,$28,$38+$80 ; ACS + DEFB $26,$39,$33+$80 ; ATN + DEFB $31,$33+$80 ; LN + DEFB $2A,$3D,$35+$80 ; EXP + DEFB $2E,$33,$39+$80 ; INT + DEFB $38,$36,$37+$80 ; SQR + DEFB $38,$2C,$33+$80 ; SGN + DEFB $26,$27,$38+$80 ; ABS + DEFB $35,$2A,$2A,$30+$80 ; PEEK + DEFB $3A,$38,$37+$80 ; USR + DEFB $38,$39,$37,$0D+$80 ; STR$ + DEFB $28,$2D,$37,$0D+$80 ; CHR$ + DEFB $33,$34,$39+$80 ; NOT + DEFB $17,$17+$80 ; ** + DEFB $34,$37+$80 ; OR + DEFB $26,$33,$29+$80 ; AND + DEFB $13,$14+$80 ; <= + DEFB $12,$14+$80 ; >= + DEFB $13,$12+$80 ; <> + DEFB $39,$2D,$2A,$33+$80 ; THEN + DEFB $39,$34+$80 ; TO + DEFB $38,$39,$2A,$35+$80 ; STEP + DEFB $31,$35,$37,$2E,$33,$39+$80 ; LPRINT + DEFB $31,$31,$2E,$38,$39+$80 ; LLIST + DEFB $38,$39,$34,$35+$80 ; STOP + DEFB $38,$31,$34,$3C+$80 ; SLOW + DEFB $2B,$26,$38,$39+$80 ; FAST + DEFB $33,$2A,$3C+$80 ; NEW + DEFB $38,$28,$37,$34,$31,$31+$80 ; SCROLL + DEFB $28,$34,$33,$39+$80 ; CONT + DEFB $29,$2E,$32+$80 ; DIM + DEFB $37,$2A,$32+$80 ; REM + DEFB $2B,$34,$37+$80 ; FOR + DEFB $2C,$34,$39,$34+$80 ; GOTO + DEFB $2C,$34,$38,$3A,$27+$80 ; GOSUB + DEFB $2E,$33,$35,$3A,$39+$80 ; INPUT + DEFB $31,$34,$26,$29+$80 ; LOAD + DEFB $31,$2E,$38,$39+$80 ; LIST + DEFB $31,$2A,$39+$80 ; LET + DEFB $35,$26,$3A,$38,$2A+$80 ; PAUSE + DEFB $33,$2A,$3D,$39+$80 ; NEXT + DEFB $35,$34,$30,$2A+$80 ; POKE + DEFB $35,$37,$2E,$33,$39+$80 ; PRINT + DEFB $35,$31,$34,$39+$80 ; PLOT + DEFB $37,$3A,$33+$80 ; RUN + DEFB $38,$26,$3B,$2A+$80 ; SAVE + DEFB $37,$26,$33,$29+$80 ; RAND + DEFB $2E,$2B+$80 ; IF + DEFB $28,$31,$38+$80 ; CLS + DEFB $3A,$33,$35,$31,$34,$39+$80 ; UNPLOT + DEFB $28,$31,$2A,$26,$37+$80 ; CLEAR + DEFB $37,$2A,$39,$3A,$37,$33+$80 ; RETURN + DEFB $28,$34,$35,$3E+$80 ; COPY + DEFB $37,$33,$29+$80 ; RND + DEFB $2E,$33,$30,$2A,$3E,$0D+$80 ; INKEY$ + DEFB $35,$2E+$80 ; PI + + +; ------------------------------ +; THE 'LOAD-SAVE UPDATE' ROUTINE +; ------------------------------ +; +; + +;; LOAD/SAVE +L01FC: INC HL ; + EX DE,HL ; + LD HL,($4014) ; system variable edit line E_LINE. + SCF ; set carry flag + SBC HL,DE ; + EX DE,HL ; + RET NC ; return if more bytes to load/save. + + POP HL ; else drop return address + +; ---------------------- +; THE 'DISPLAY' ROUTINES +; ---------------------- +; +; + +;; SLOW/FAST +L0207: LD HL,$403B ; Address the system variable CDFLAG. + LD A,(HL) ; Load value to the accumulator. + RLA ; rotate bit 6 to position 7. + XOR (HL) ; exclusive or with original bit 7. + RLA ; rotate result out to carry. + RET NC ; return if both bits were the same. + +; Now test if this really is a ZX81 or a ZX80 running the upgraded ROM. +; The standard ZX80 did not have an NMI generator. + + LD A,$7F ; Load accumulator with %011111111 + EX AF,AF' ; save in AF' + + LD B,$11 ; A counter within which an NMI should occur + ; if this is a ZX81. + OUT ($FE),A ; start the NMI generator. + +; Note that if this is a ZX81 then the NMI will increment AF'. + +;; LOOP-11 +L0216: DJNZ L0216 ; self loop to give the NMI a chance to kick in. + ; = 16*13 clock cycles + 8 = 216 clock cycles. + + OUT ($FD),A ; Turn off the NMI generator. + EX AF,AF' ; bring back the AF' value. + RLA ; test bit 7. + JR NC,L0226 ; forward, if bit 7 is still reset, to NO-SLOW. + +; If the AF' was incremented then the NMI generator works and SLOW mode can +; be set. + + SET 7,(HL) ; Indicate SLOW mode - Compute and Display. + + PUSH AF ; * Save Main Registers + PUSH BC ; ** + PUSH DE ; *** + PUSH HL ; **** + + JR L0229 ; skip forward - to DISPLAY-1. + +; --- + +;; NO-SLOW +L0226: RES 6,(HL) ; reset bit 6 of CDFLAG. + RET ; return. + +; ----------------------- +; THE 'MAIN DISPLAY' LOOP +; ----------------------- +; This routine is executed once for every frame displayed. + +;; DISPLAY-1 +L0229: LD HL,($4034) ; fetch two-byte system variable FRAMES. + DEC HL ; decrement frames counter. + +;; DISPLAY-P +L022D: LD A,$7F ; prepare a mask + AND H ; pick up bits 6-0 of H. + OR L ; and any bits of L. + LD A,H ; reload A with all bits of H for PAUSE test. + +; Note both branches must take the same time. + + JR NZ,L0237 ; (12/7) forward if bits 14-0 are not zero + ; to ANOTHER + + RLA ; (4) test bit 15 of FRAMES. + JR L0239 ; (12) forward with result to OVER-NC + +; --- + +;; ANOTHER +L0237: LD B,(HL) ; (7) Note. Harmless Nonsensical Timing weight. + SCF ; (4) Set Carry Flag. + +; Note. the branch to here takes either (12)(7)(4) cyles or (7)(4)(12) cycles. + +;; OVER-NC +L0239: LD H,A ; (4) set H to zero + LD ($4034),HL ; (16) update system variable FRAMES + RET NC ; (11/5) return if FRAMES is in use by PAUSE + ; command. + +;; DISPLAY-2 +L023E: CALL L02BB ; routine KEYBOARD gets the key row in H and + ; the column in L. Reading the ports also starts + ; the TV frame synchronization pulse. (VSYNC) + + LD BC,($4025) ; fetch the last key values read from LAST_K + LD ($4025),HL ; update LAST_K with new values. + + LD A,B ; load A with previous column - will be $FF if + ; there was no key. + ADD A,$02 ; adding two will set carry if no previous key. + + SBC HL,BC ; subtract with the carry the two key values. + +; If the same key value has been returned twice then HL will be zero. + + LD A,($4027) ; fetch system variable DEBOUNCE + OR H ; and OR with both bytes of the difference + OR L ; setting the zero flag for the upcoming branch. + + LD E,B ; transfer the column value to E + LD B,$0B ; and load B with eleven + + LD HL,$403B ; address system variable CDFLAG + RES 0,(HL) ; reset the rightmost bit of CDFLAG + JR NZ,L0264 ; skip forward if debounce/diff >0 to NO-KEY + + BIT 7,(HL) ; test compute and display bit of CDFLAG + SET 0,(HL) ; set the rightmost bit of CDFLAG. + RET Z ; return if bit 7 indicated fast mode. + + DEC B ; (4) decrement the counter. + NOP ; (4) Timing - 4 clock cycles. ?? + SCF ; (4) Set Carry Flag + +;; NO-KEY +L0264: LD HL,$4027 ; sv DEBOUNCE + CCF ; Complement Carry Flag + RL B ; rotate left B picking up carry + ; C<-76543210<-C + +;; LOOP-B +L026A: DJNZ L026A ; self-loop while B>0 to LOOP-B + + LD B,(HL) ; fetch value of DEBOUNCE to B + LD A,E ; transfer column value + CP $FE ; + SBC A,A ; + LD B,$1F ; + OR (HL) ; + AND B ; + RRA ; + LD (HL),A ; + + OUT ($FF),A ; end the TV frame synchronization pulse. + + LD HL,($400C) ; (12) set HL to the Display File from D_FILE + SET 7,H ; (8) set bit 15 to address the echo display. + + CALL L0292 ; (17) routine DISPLAY-3 displays the top set + ; of blank lines. + +; --------------------- +; THE 'VIDEO-1' ROUTINE +; --------------------- + +;; R-IX-1 +L0281: LD A,R ; (9) Harmless Nonsensical Timing or something + ; very clever? + LD BC,$1901 ; (10) 25 lines, 1 scanline in first. + LD A,$F5 ; (7) This value will be loaded into R and + ; ensures that the cycle starts at the right + ; part of the display - after 32nd character + ; position. + + CALL L02B5 ; (17) routine DISPLAY-5 completes the current + ; blank line and then generates the display of + ; the live picture using INT interrupts + ; The final interrupt returns to the next + ; address. + +L028B: DEC HL ; point HL to the last NEWLINE/HALT. + + CALL L0292 ; routine DISPLAY-3 displays the bottom set of + ; blank lines. + +; --- + +;; R-IX-2 +L028F: JP L0229 ; JUMP back to DISPLAY-1 + +; --------------------------------- +; THE 'DISPLAY BLANK LINES' ROUTINE +; --------------------------------- +; This subroutine is called twice (see above) to generate first the blank +; lines at the top of the television display and then the blank lines at the +; bottom of the display. + +;; DISPLAY-3 +L0292: POP IX ; pop the return address to IX register. + ; will be either L0281 or L028F - see above. + + LD C,(IY+$28) ; load C with value of system constant MARGIN. + BIT 7,(IY+$3B) ; test CDFLAG for compute and display. + JR Z,L02A9 ; forward, with FAST mode, to DISPLAY-4 + + LD A,C ; move MARGIN to A - 31d or 55d. + NEG ; Negate + INC A ; + EX AF,AF' ; place negative count of blank lines in A' + + OUT ($FE),A ; enable the NMI generator. + + POP HL ; **** + POP DE ; *** + POP BC ; ** + POP AF ; * Restore Main Registers + + RET ; return - end of interrupt. Return is to + ; user's program - BASIC or machine code. + ; which will be interrupted by every NMI. + +; ------------------------ +; THE 'FAST MODE' ROUTINES +; ------------------------ + +;; DISPLAY-4 +L02A9: LD A,$FC ; (7) load A with first R delay value + LD B,$01 ; (7) one row only. + + CALL L02B5 ; (17) routine DISPLAY-5 + + DEC HL ; (6) point back to the HALT. + EX (SP),HL ; (19) Harmless Nonsensical Timing if paired. + EX (SP),HL ; (19) Harmless Nonsensical Timing. + JP (IX) ; (8) to L0281 or L028F + +; -------------------------- +; THE 'DISPLAY-5' SUBROUTINE +; -------------------------- +; This subroutine is called from SLOW mode and FAST mode to generate the +; central TV picture. With SLOW mode the R register is incremented, with +; each instruction, to $F7 by the time it completes. With fast mode, the +; final R value will be $FF and an interrupt will occur as soon as the +; Program Counter reaches the HALT. (24 clock cycles) + +;; DISPLAY-5 +L02B5: LD R,A ; (9) Load R from A. R = slow: $F5 fast: $FC + LD A,$DD ; (7) load future R value. $F6 $FD + + EI ; (4) Enable Interrupts $F7 $FE + + JP (HL) ; (4) jump to the echo display. $F8 $FF + +; ---------------------------------- +; THE 'KEYBOARD SCANNING' SUBROUTINE +; ---------------------------------- +; The keyboard is read during the vertical sync interval while no video is +; being displayed. Reading a port with address bit 0 low i.e. $FE starts the +; vertical sync pulse. + +;; KEYBOARD +L02BB: LD HL,$FFFF ; (16) prepare a buffer to take key. + LD BC,$FEFE ; (20) set BC to port $FEFE. The B register, + ; with its single reset bit also acts as + ; an 8-counter. + IN A,(C) ; (11) read the port - all 16 bits are put on + ; the address bus. Start VSYNC pulse. + OR $01 ; (7) set the rightmost bit so as to ignore + ; the SHIFT key. + +;; EACH-LINE +L02C5: OR $E0 ; [7] OR %11100000 + LD D,A ; [4] transfer to D. + CPL ; [4] complement - only bits 4-0 meaningful now. + CP $01 ; [7] sets carry if A is zero. + SBC A,A ; [4] $FF if $00 else zero. + OR B ; [7] $FF or port FE,FD,FB.... + AND L ; [4] unless more than one key, L will still be + ; $FF. if more than one key is pressed then A is + ; now invalid. + LD L,A ; [4] transfer to L. + +; now consider the column identifier. + + LD A,H ; [4] will be $FF if no previous keys. + AND D ; [4] 111xxxxx + LD H,A ; [4] transfer A to H + +; since only one key may be pressed, H will, if valid, be one of +; 11111110, 11111101, 11111011, 11110111, 11101111 +; reading from the outer column, say Q, to the inner column, say T. + + RLC B ; [8] rotate the 8-counter/port address. + ; sets carry if more to do. + IN A,(C) ; [10] read another half-row. + ; all five bits this time. + + JR C,L02C5 ; [12](7) loop back, until done, to EACH-LINE + +; The last row read is SHIFT,Z,X,C,V for the second time. + + RRA ; (4) test the shift key - carry will be reset + ; if the key is pressed. + RL H ; (8) rotate left H picking up the carry giving + ; column values - + ; $FD, $FB, $F7, $EF, $DF. + ; or $FC, $FA, $F6, $EE, $DE if shifted. + +; We now have H identifying the column and L identifying the row in the +; keyboard matrix. + +; This is a good time to test if this is an American or British machine. +; The US machine has an extra diode that causes bit 6 of a byte read from +; a port to be reset. + + RLA ; (4) compensate for the shift test. + RLA ; (4) rotate bit 7 out. + RLA ; (4) test bit 6. + + SBC A,A ; (4) $FF or $00 {USA} + AND $18 ; (7) $18 or $00 + ADD A,$1F ; (7) $37 or $1F + +; result is either 31 (USA) or 55 (UK) blank lines above and below the TV +; picture. + + LD ($4028),A ; (13) update system variable MARGIN + + RET ; (10) return + +; ------------------------------ +; THE 'SET FAST MODE' SUBROUTINE +; ------------------------------ +; +; + +;; SET-FAST +L02E7: BIT 7,(IY+$3B) ; sv CDFLAG + RET Z ; + + HALT ; Wait for Interrupt + OUT ($FD),A ; + RES 7,(IY+$3B) ; sv CDFLAG + RET ; return. + + +; -------------- +; THE 'REPORT-F' +; -------------- + +;; REPORT-F +L02F4: RST 08H ; ERROR-1 + DEFB $0E ; Error Report: No Program Name supplied. + +; -------------------------- +; THE 'SAVE COMMAND' ROUTINE +; -------------------------- +; +; + +;; SAVE +L02F6: CALL L03A8 ; routine NAME + JR C,L02F4 ; back with null name to REPORT-F above. + + EX DE,HL ; + LD DE,$12CB ; five seconds timing value + +;; HEADER +L02FF: CALL L0F46 ; routine BREAK-1 + JR NC,L0332 ; to BREAK-2 + +;; DELAY-1 +L0304: DJNZ L0304 ; to DELAY-1 + + DEC DE ; + LD A,D ; + OR E ; + JR NZ,L02FF ; back for delay to HEADER + +;; OUT-NAME +L030B: CALL L031E ; routine OUT-BYTE + BIT 7,(HL) ; test for inverted bit. + INC HL ; address next character of name. + JR Z,L030B ; back if not inverted to OUT-NAME + +; now start saving the system variables onwards. + + LD HL,$4009 ; set start of area to VERSN thereby + ; preserving RAMTOP etc. + +;; OUT-PROG +L0316: CALL L031E ; routine OUT-BYTE + + CALL L01FC ; routine LOAD/SAVE >> + JR L0316 ; loop back to OUT-PROG + +; ------------------------- +; THE 'OUT-BYTE' SUBROUTINE +; ------------------------- +; This subroutine outputs a byte a bit at a time to a domestic tape recorder. + +;; OUT-BYTE +L031E: LD E,(HL) ; fetch byte to be saved. + SCF ; set carry flag - as a marker. + +;; EACH-BIT +L0320: RL E ; C < 76543210 < C + RET Z ; return when the marker bit has passed + ; right through. >> + + SBC A,A ; $FF if set bit or $00 with no carry. + AND $05 ; $05 $00 + ADD A,$04 ; $09 $04 + LD C,A ; transfer timer to C. a set bit has a longer + ; pulse than a reset bit. + +;; PULSES +L0329: OUT ($FF),A ; pulse to cassette. + LD B,$23 ; set timing constant + +;; DELAY-2 +L032D: DJNZ L032D ; self-loop to DELAY-2 + + CALL L0F46 ; routine BREAK-1 test for BREAK key. + +;; BREAK-2 +L0332: JR NC,L03A6 ; forward with break to REPORT-D + + LD B,$1E ; set timing value. + +;; DELAY-3 +L0336: DJNZ L0336 ; self-loop to DELAY-3 + + DEC C ; decrement counter + JR NZ,L0329 ; loop back to PULSES + +;; DELAY-4 +L033B: AND A ; clear carry for next bit test. + DJNZ L033B ; self loop to DELAY-4 (B is zero - 256) + + JR L0320 ; loop back to EACH-BIT + +; -------------------------- +; THE 'LOAD COMMAND' ROUTINE +; -------------------------- +; +; + +;; LOAD +L0340: CALL L03A8 ; routine NAME + +; DE points to start of name in RAM. + + RL D ; pick up carry + RRC D ; carry now in bit 7. + +;; NEXT-PROG +L0347: CALL L034C ; routine IN-BYTE + JR L0347 ; loop to NEXT-PROG + +; ------------------------ +; THE 'IN-BYTE' SUBROUTINE +; ------------------------ + +;; IN-BYTE +L034C: LD C,$01 ; prepare an eight counter 00000001. + +;; NEXT-BIT +L034E: LD B,$00 ; set counter to 256 + +;; BREAK-3 +L0350: LD A,$7F ; read the keyboard row + IN A,($FE) ; with the SPACE key. + + OUT ($FF),A ; output signal to screen. + + RRA ; test for SPACE pressed. + JR NC,L03A2 ; forward if so to BREAK-4 + + RLA ; reverse above rotation + RLA ; test tape bit. + JR C,L0385 ; forward if set to GET-BIT + + DJNZ L0350 ; loop back to BREAK-3 + + POP AF ; drop the return address. + CP D ; ugh. + +;; RESTART +L0361: JP NC,L03E5 ; jump forward to INITIAL if D is zero + ; to reset the system + ; if the tape signal has timed out for example + ; if the tape is stopped. Not just a simple + ; report as some system variables will have + ; been overwritten. + + LD H,D ; else transfer the start of name + LD L,E ; to the HL register + +;; IN-NAME +L0366: CALL L034C ; routine IN-BYTE is sort of recursion for name + ; part. received byte in C. + BIT 7,D ; is name the null string ? + LD A,C ; transfer byte to A. + JR NZ,L0371 ; forward with null string to MATCHING + + CP (HL) ; else compare with string in memory. + JR NZ,L0347 ; back with mis-match to NEXT-PROG + ; (seemingly out of subroutine but return + ; address has been dropped). + + +;; MATCHING +L0371: INC HL ; address next character of name + RLA ; test for inverted bit. + JR NC,L0366 ; back if not to IN-NAME + +; the name has been matched in full. +; proceed to load the data but first increment the high byte of E_LINE, which +; is one of the system variables to be loaded in. Since the low byte is loaded +; before the high byte, it is possible that, at the in-between stage, a false +; value could cause the load to end prematurely - see LOAD/SAVE check. + + INC (IY+$15) ; increment system variable E_LINE_hi. + LD HL,$4009 ; start loading at system variable VERSN. + +;; IN-PROG +L037B: LD D,B ; set D to zero as indicator. + CALL L034C ; routine IN-BYTE loads a byte + LD (HL),C ; insert assembled byte in memory. + CALL L01FC ; routine LOAD/SAVE >> + JR L037B ; loop back to IN-PROG + +; --- + +; this branch assembles a full byte before exiting normally +; from the IN-BYTE subroutine. + +;; GET-BIT +L0385: PUSH DE ; save the + LD E,$94 ; timing value. + +;; TRAILER +L0388: LD B,$1A ; counter to twenty six. + +;; COUNTER +L038A: DEC E ; decrement the measuring timer. + IN A,($FE) ; read the + RLA ; + BIT 7,E ; + LD A,E ; + JR C,L0388 ; loop back with carry to TRAILER + + DJNZ L038A ; to COUNTER + + POP DE ; + JR NZ,L039C ; to BIT-DONE + + CP $56 ; + JR NC,L034E ; to NEXT-BIT + +;; BIT-DONE +L039C: CCF ; complement carry flag + RL C ; + JR NC,L034E ; to NEXT-BIT + + RET ; return with full byte. + +; --- + +; if break is pressed while loading data then perform a reset. +; if break pressed while waiting for program on tape then OK to break. + +;; BREAK-4 +L03A2: LD A,D ; transfer indicator to A. + AND A ; test for zero. + JR Z,L0361 ; back if so to RESTART + + +;; REPORT-D +L03A6: RST 08H ; ERROR-1 + DEFB $0C ; Error Report: BREAK - CONT repeats + +; ----------------------------- +; THE 'PROGRAM NAME' SUBROUTINE +; ----------------------------- +; +; + +;; NAME +L03A8: CALL L0F55 ; routine SCANNING + LD A,($4001) ; sv FLAGS + ADD A,A ; + JP M,L0D9A ; to REPORT-C + + POP HL ; + RET NC ; + + PUSH HL ; + CALL L02E7 ; routine SET-FAST + CALL L13F8 ; routine STK-FETCH + LD H,D ; + LD L,E ; + DEC C ; + RET M ; + + ADD HL,BC ; + SET 7,(HL) ; + RET ; + +; ------------------------- +; THE 'NEW' COMMAND ROUTINE +; ------------------------- +; +; + +;; NEW +L03C3: CALL L02E7 ; routine SET-FAST + LD BC,($4004) ; fetch value of system variable RAMTOP + DEC BC ; point to last system byte. + +; ----------------------- +; THE 'RAM CHECK' ROUTINE +; ----------------------- +; +; + +;; RAM-CHECK +L03CB: LD H,B ; + LD L,C ; + LD A,$3F ; + +;; RAM-FILL +L03CF: LD (HL),$02 ; + DEC HL ; + CP H ; + JR NZ,L03CF ; to RAM-FILL + +;; RAM-READ +L03D5: AND A ; + SBC HL,BC ; + ADD HL,BC ; + INC HL ; + JR NC,L03E2 ; to SET-TOP + + DEC (HL) ; + JR Z,L03E2 ; to SET-TOP + + DEC (HL) ; + JR Z,L03D5 ; to RAM-READ + +;; SET-TOP +L03E2: LD ($4004),HL ; set system variable RAMTOP to first byte + ; above the BASIC system area. + +; ---------------------------- +; THE 'INITIALIZATION' ROUTINE +; ---------------------------- +; +; + +;; INITIAL +L03E5: LD HL,($4004) ; fetch system variable RAMTOP. + DEC HL ; point to last system byte. + LD (HL),$3E ; make GO SUB end-marker $3E - too high for + ; high order byte of line number. + ; (was $3F on ZX80) + DEC HL ; point to unimportant low-order byte. + LD SP,HL ; and initialize the stack-pointer to this + ; location. + DEC HL ; point to first location on the machine stack + DEC HL ; which will be filled by next CALL/PUSH. + LD ($4002),HL ; set the error stack pointer ERR_SP to + ; the base of the now empty machine stack. + +; Now set the I register so that the video hardware knows where to find the +; character set. This ROM only uses the character set when printing to +; the ZX Printer. The TV picture is formed by the external video hardware. +; Consider also, that this 8K ROM can be retro-fitted to the ZX80 instead of +; its original 4K ROM so the video hardware could be on the ZX80. + + LD A,$1E ; address for this ROM is $1E00. + LD I,A ; set I register from A. + IM 1 ; select Z80 Interrupt Mode 1. + + LD IY,$4000 ; set IY to the start of RAM so that the + ; system variables can be indexed. + LD (IY+$3B),$40 ; set CDFLAG 0100 0000. Bit 6 indicates + ; Compute nad Display required. + + LD HL,$407D ; The first location after System Variables - + ; 16509 decimal. + LD ($400C),HL ; set system variable D_FILE to this value. + LD B,$19 ; prepare minimal screen of 24 NEWLINEs + ; following an initial NEWLINE. + +;; LINE +L0408: LD (HL),$76 ; insert NEWLINE (HALT instruction) + INC HL ; point to next location. + DJNZ L0408 ; loop back for all twenty five to LINE + + LD ($4010),HL ; set system variable VARS to next location + + CALL L149A ; routine CLEAR sets $80 end-marker and the + ; dynamic memory pointers E_LINE, STKBOT and + ; STKEND. + +;; N/L-ONLY +L0413: CALL L14AD ; routine CURSOR-IN inserts the cursor and + ; end-marker in the Edit Line also setting + ; size of lower display to two lines. + + CALL L0207 ; routine SLOW/FAST selects COMPUTE and DISPLAY + +; --------------------------- +; THE 'BASIC LISTING' SECTION +; --------------------------- +; +; + +;; UPPER +L0419: CALL L0A2A ; routine CLS + LD HL,($400A) ; sv E_PPC_lo + LD DE,($4023) ; sv S_TOP_lo + AND A ; + SBC HL,DE ; + EX DE,HL ; + JR NC,L042D ; to ADDR-TOP + + ADD HL,DE ; + LD ($4023),HL ; sv S_TOP_lo + +;; ADDR-TOP +L042D: CALL L09D8 ; routine LINE-ADDR + JR Z,L0433 ; to LIST-TOP + + EX DE,HL ; + +;; LIST-TOP +L0433: CALL L073E ; routine LIST-PROG + DEC (IY+$1E) ; sv BERG + JR NZ,L0472 ; to LOWER + + LD HL,($400A) ; sv E_PPC_lo + CALL L09D8 ; routine LINE-ADDR + LD HL,($4016) ; sv CH_ADD_lo + SCF ; Set Carry Flag + SBC HL,DE ; + LD HL,$4023 ; sv S_TOP_lo + JR NC,L0457 ; to INC-LINE + + EX DE,HL ; + LD A,(HL) ; + INC HL ; + LDI ; + LD (DE),A ; + JR L0419 ; to UPPER + +; --- + +;; DOWN-KEY +L0454: LD HL,$400A ; sv E_PPC_lo + +;; INC-LINE +L0457: LD E,(HL) ; + INC HL ; + LD D,(HL) ; + PUSH HL ; + EX DE,HL ; + INC HL ; + CALL L09D8 ; routine LINE-ADDR + CALL L05BB ; routine LINE-NO + POP HL ; + +;; KEY-INPUT +L0464: BIT 5,(IY+$2D) ; sv FLAGX + JR NZ,L0472 ; forward to LOWER + + LD (HL),D ; + DEC HL ; + LD (HL),E ; + JR L0419 ; to UPPER + +; ---------------------------- +; THE 'EDIT LINE COPY' SECTION +; ---------------------------- +; This routine sets the edit line to just the cursor when +; 1) There is not enough memory to edit a BASIC line. +; 2) The edit key is used during input. +; The entry point LOWER + + +;; EDIT-INP +L046F: CALL L14AD ; routine CURSOR-IN sets cursor only edit line. + +; -> + +;; LOWER +L0472: LD HL,($4014) ; fetch edit line start from E_LINE. + +;; EACH-CHAR +L0475: LD A,(HL) ; fetch a character from edit line. + CP $7E ; compare to the number marker. + JR NZ,L0482 ; forward if not to END-LINE + + LD BC,$0006 ; else six invisible bytes to be removed. + CALL L0A60 ; routine RECLAIM-2 + JR L0475 ; back to EACH-CHAR + +; --- + +;; END-LINE +L0482: CP $76 ; + INC HL ; + JR NZ,L0475 ; to EACH-CHAR + +;; EDIT-LINE +L0487: CALL L0537 ; routine CURSOR sets cursor K or L. + +;; EDIT-ROOM +L048A: CALL L0A1F ; routine LINE-ENDS + LD HL,($4014) ; sv E_LINE_lo + LD (IY+$00),$FF ; sv ERR_NR + CALL L0766 ; routine COPY-LINE + BIT 7,(IY+$00) ; sv ERR_NR + JR NZ,L04C1 ; to DISPLAY-6 + + LD A,($4022) ; sv DF_SZ + CP $18 ; + JR NC,L04C1 ; to DISPLAY-6 + + INC A ; + LD ($4022),A ; sv DF_SZ + LD B,A ; + LD C,$01 ; + CALL L0918 ; routine LOC-ADDR + LD D,H ; + LD E,L ; + LD A,(HL) ; + +;; FREE-LINE +L04B1: DEC HL ; + CP (HL) ; + JR NZ,L04B1 ; to FREE-LINE + + INC HL ; + EX DE,HL ; + LD A,($4005) ; sv RAMTOP_hi + CP $4D ; + CALL C,L0A5D ; routine RECLAIM-1 + JR L048A ; to EDIT-ROOM + +; -------------------------- +; THE 'WAIT FOR KEY' SECTION +; -------------------------- +; +; + +;; DISPLAY-6 +L04C1: LD HL,$0000 ; + LD ($4018),HL ; sv X_PTR_lo + + LD HL,$403B ; system variable CDFLAG + BIT 7,(HL) ; + + CALL Z,L0229 ; routine DISPLAY-1 + +;; SLOW-DISP +L04CF: BIT 0,(HL) ; + JR Z,L04CF ; to SLOW-DISP + + LD BC,($4025) ; sv LAST_K + CALL L0F4B ; routine DEBOUNCE + CALL L07BD ; routine DECODE + + JR NC,L0472 ; back to LOWER + +; ------------------------------- +; THE 'KEYBOARD DECODING' SECTION +; ------------------------------- +; The decoded key value is in E and HL points to the position in the +; key table. D contains zero. + +;; K-DECODE +L04DF: LD A,($4006) ; Fetch value of system variable MODE + DEC A ; test the three values together + + JP M,L0508 ; forward, if was zero, to FETCH-2 + + JR NZ,L04F7 ; forward, if was 2, to FETCH-1 + +; The original value was one and is now zero. + + LD ($4006),A ; update the system variable MODE + + DEC E ; reduce E to range $00 - $7F + LD A,E ; place in A + SUB $27 ; subtract 39 setting carry if range 00 - 38 + JR C,L04F2 ; forward, if so, to FUNC-BASE + + LD E,A ; else set E to reduced value + +;; FUNC-BASE +L04F2: LD HL,L00CC ; address of K-FUNCT table for function keys. + JR L0505 ; forward to TABLE-ADD + +; --- + +;; FETCH-1 +L04F7: LD A,(HL) ; + CP $76 ; + JR Z,L052B ; to K/L-KEY + + CP $40 ; + SET 7,A ; + JR C,L051B ; to ENTER + + LD HL,$00C7 ; (expr reqd) + +;; TABLE-ADD +L0505: ADD HL,DE ; + JR L0515 ; to FETCH-3 + +; --- + +;; FETCH-2 +L0508: LD A,(HL) ; + BIT 2,(IY+$01) ; sv FLAGS - K or L mode ? + JR NZ,L0516 ; to TEST-CURS + + ADD A,$C0 ; + CP $E6 ; + JR NC,L0516 ; to TEST-CURS + +;; FETCH-3 +L0515: LD A,(HL) ; + +;; TEST-CURS +L0516: CP $F0 ; + JP PE,L052D ; to KEY-SORT + +;; ENTER +L051B: LD E,A ; + CALL L0537 ; routine CURSOR + + LD A,E ; + CALL L0526 ; routine ADD-CHAR + +;; BACK-NEXT +L0523: JP L0472 ; back to LOWER + +; ------------------------------ +; THE 'ADD CHARACTER' SUBROUTINE +; ------------------------------ +; +; + +;; ADD-CHAR +L0526: CALL L099B ; routine ONE-SPACE + LD (DE),A ; + RET ; + +; ------------------------- +; THE 'CURSOR KEYS' ROUTINE +; ------------------------- +; +; + +;; K/L-KEY +L052B: LD A,$78 ; + +;; KEY-SORT +L052D: LD E,A ; + LD HL,$0482 ; base address of ED-KEYS (exp reqd) + ADD HL,DE ; + ADD HL,DE ; + LD C,(HL) ; + INC HL ; + LD B,(HL) ; + PUSH BC ; + +;; CURSOR +L0537: LD HL,($4014) ; sv E_LINE_lo + BIT 5,(IY+$2D) ; sv FLAGX + JR NZ,L0556 ; to L-MODE + +;; K-MODE +L0540: RES 2,(IY+$01) ; sv FLAGS - Signal use K mode + +;; TEST-CHAR +L0544: LD A,(HL) ; + CP $7F ; + RET Z ; return + + INC HL ; + CALL L07B4 ; routine NUMBER + JR Z,L0544 ; to TEST-CHAR + + CP $26 ; + JR C,L0544 ; to TEST-CHAR + + CP $DE ; + JR Z,L0540 ; to K-MODE + +;; L-MODE +L0556: SET 2,(IY+$01) ; sv FLAGS - Signal use L mode + JR L0544 ; to TEST-CHAR + +; -------------------------- +; THE 'CLEAR-ONE' SUBROUTINE +; -------------------------- +; +; + +;; CLEAR-ONE +L055C: LD BC,$0001 ; + JP L0A60 ; to RECLAIM-2 + + + +; ------------------------ +; THE 'EDITING KEYS' TABLE +; ------------------------ +; +; + +;; ED-KEYS +L0562: DEFW L059F ; Address: $059F; Address: UP-KEY + DEFW L0454 ; Address: $0454; Address: DOWN-KEY + DEFW L0576 ; Address: $0576; Address: LEFT-KEY + DEFW L057F ; Address: $057F; Address: RIGHT-KEY + DEFW L05AF ; Address: $05AF; Address: FUNCTION + DEFW L05C4 ; Address: $05C4; Address: EDIT-KEY + DEFW L060C ; Address: $060C; Address: N/L-KEY + DEFW L058B ; Address: $058B; Address: RUBOUT + DEFW L05AF ; Address: $05AF; Address: FUNCTION + DEFW L05AF ; Address: $05AF; Address: FUNCTION + + +; ------------------------- +; THE 'CURSOR LEFT' ROUTINE +; ------------------------- +; +; + +;; LEFT-KEY +L0576: CALL L0593 ; routine LEFT-EDGE + LD A,(HL) ; + LD (HL),$7F ; + INC HL ; + JR L0588 ; to GET-CODE + +; -------------------------- +; THE 'CURSOR RIGHT' ROUTINE +; -------------------------- +; +; + +;; RIGHT-KEY +L057F: INC HL ; + LD A,(HL) ; + CP $76 ; + JR Z,L059D ; to ENDED-2 + + LD (HL),$7F ; + DEC HL ; + +;; GET-CODE +L0588: LD (HL),A ; + +;; ENDED-1 +L0589: JR L0523 ; to BACK-NEXT + +; -------------------- +; THE 'RUBOUT' ROUTINE +; -------------------- +; +; + +;; RUBOUT +L058B: CALL L0593 ; routine LEFT-EDGE + CALL L055C ; routine CLEAR-ONE + JR L0589 ; to ENDED-1 + +; ------------------------ +; THE 'ED-EDGE' SUBROUTINE +; ------------------------ +; +; + +;; LEFT-EDGE +L0593: DEC HL ; + LD DE,($4014) ; sv E_LINE_lo + LD A,(DE) ; + CP $7F ; + RET NZ ; + + POP DE ; + +;; ENDED-2 +L059D: JR L0589 ; to ENDED-1 + +; ----------------------- +; THE 'CURSOR UP' ROUTINE +; ----------------------- +; +; + +;; UP-KEY +L059F: LD HL,($400A) ; sv E_PPC_lo + CALL L09D8 ; routine LINE-ADDR + EX DE,HL ; + CALL L05BB ; routine LINE-NO + LD HL,$400B ; point to system variable E_PPC_hi + JP L0464 ; jump back to KEY-INPUT + +; -------------------------- +; THE 'FUNCTION KEY' ROUTINE +; -------------------------- +; +; + +;; FUNCTION +L05AF: LD A,E ; + AND $07 ; + LD ($4006),A ; sv MODE + JR L059D ; back to ENDED-2 + +; ------------------------------------ +; THE 'COLLECT LINE NUMBER' SUBROUTINE +; ------------------------------------ +; +; + +;; ZERO-DE +L05B7: EX DE,HL ; + LD DE,L04C1 + 1 ; $04C2 - a location addressing two zeros. + +; -> + +;; LINE-NO +L05BB: LD A,(HL) ; + AND $C0 ; + JR NZ,L05B7 ; to ZERO-DE + + LD D,(HL) ; + INC HL ; + LD E,(HL) ; + RET ; + +; ---------------------- +; THE 'EDIT KEY' ROUTINE +; ---------------------- +; +; + +;; EDIT-KEY +L05C4: CALL L0A1F ; routine LINE-ENDS clears lower display. + + LD HL,L046F ; Address: EDIT-INP + PUSH HL ; ** is pushed as an error looping address. + + BIT 5,(IY+$2D) ; test FLAGX + RET NZ ; indirect jump if in input mode + ; to L046F, EDIT-INP (begin again). + +; + + LD HL,($4014) ; fetch E_LINE + LD ($400E),HL ; and use to update the screen cursor DF_CC + +; so now RST $10 will print the line numbers to the edit line instead of screen. +; first make sure that no newline/out of screen can occur while sprinting the +; line numbers to the edit line. + + LD HL,$1821 ; prepare line 0, column 0. + LD ($4039),HL ; update S_POSN with these dummy values. + + LD HL,($400A) ; fetch current line from E_PPC may be a + ; non-existent line e.g. last line deleted. + CALL L09D8 ; routine LINE-ADDR gets address or that of + ; the following line. + CALL L05BB ; routine LINE-NO gets line number if any in DE + ; leaving HL pointing at second low byte. + + LD A,D ; test the line number for zero. + OR E ; + RET Z ; return if no line number - no program to edit. + + DEC HL ; point to high byte. + CALL L0AA5 ; routine OUT-NO writes number to edit line. + + INC HL ; point to length bytes. + LD C,(HL) ; low byte to C. + INC HL ; + LD B,(HL) ; high byte to B. + + INC HL ; point to first character in line. + LD DE,($400E) ; fetch display file cursor DF_CC + + LD A,$7F ; prepare the cursor character. + LD (DE),A ; and insert in edit line. + INC DE ; increment intended destination. + + PUSH HL ; * save start of BASIC. + + LD HL,$001D ; set an overhead of 29 bytes. + ADD HL,DE ; add in the address of cursor. + ADD HL,BC ; add the length of the line. + SBC HL,SP ; subtract the stack pointer. + + POP HL ; * restore pointer to start of BASIC. + + RET NC ; return if not enough room to L046F EDIT-INP. + ; the edit key appears not to work. + + LDIR ; else copy bytes from program to edit line. + ; Note. hidden floating point forms are also + ; copied to edit line. + + EX DE,HL ; transfer free location pointer to HL + + POP DE ; ** remove address EDIT-INP from stack. + + CALL L14A6 ; routine SET-STK-B sets STKEND from HL. + + JR L059D ; back to ENDED-2 and after 3 more jumps + ; to L0472, LOWER. + ; Note. The LOWER routine removes the hidden + ; floating-point numbers from the edit line. + +; ------------------------- +; THE 'NEWLINE KEY' ROUTINE +; ------------------------- +; +; + +;; N/L-KEY +L060C: CALL L0A1F ; routine LINE-ENDS + + LD HL,L0472 ; prepare address: LOWER + + BIT 5,(IY+$2D) ; sv FLAGX + JR NZ,L0629 ; to NOW-SCAN + + LD HL,($4014) ; sv E_LINE_lo + LD A,(HL) ; + CP $FF ; + JR Z,L0626 ; to STK-UPPER + + CALL L08E2 ; routine CLEAR-PRB + CALL L0A2A ; routine CLS + +;; STK-UPPER +L0626: LD HL,L0419 ; Address: UPPER + +;; NOW-SCAN +L0629: PUSH HL ; push routine address (LOWER or UPPER). + CALL L0CBA ; routine LINE-SCAN + POP HL ; + CALL L0537 ; routine CURSOR + CALL L055C ; routine CLEAR-ONE + CALL L0A73 ; routine E-LINE-NO + JR NZ,L064E ; to N/L-INP + + LD A,B ; + OR C ; + JP NZ,L06E0 ; to N/L-LINE + + DEC BC ; + DEC BC ; + LD ($4007),BC ; sv PPC_lo + LD (IY+$22),$02 ; sv DF_SZ + LD DE,($400C) ; sv D_FILE_lo + + JR L0661 ; forward to TEST-NULL + +; --- + +;; N/L-INP +L064E: CP $76 ; + JR Z,L0664 ; to N/L-NULL + + LD BC,($4030) ; sv T_ADDR_lo + CALL L0918 ; routine LOC-ADDR + LD DE,($4029) ; sv NXTLIN_lo + LD (IY+$22),$02 ; sv DF_SZ + +;; TEST-NULL +L0661: RST 18H ; GET-CHAR + CP $76 ; + +;; N/L-NULL +L0664: JP Z,L0413 ; to N/L-ONLY + + LD (IY+$01),$80 ; sv FLAGS + EX DE,HL ; + +;; NEXT-LINE +L066C: LD ($4029),HL ; sv NXTLIN_lo + EX DE,HL ; + CALL L004D ; routine TEMP-PTR-2 + CALL L0CC1 ; routine LINE-RUN + RES 1,(IY+$01) ; sv FLAGS - Signal printer not in use + LD A,$C0 ; + LD (IY+$19),A ; sv X_PTR_lo + CALL L14A3 ; routine X-TEMP + RES 5,(IY+$2D) ; sv FLAGX + BIT 7,(IY+$00) ; sv ERR_NR + JR Z,L06AE ; to STOP-LINE + + LD HL,($4029) ; sv NXTLIN_lo + AND (HL) ; + JR NZ,L06AE ; to STOP-LINE + + LD D,(HL) ; + INC HL ; + LD E,(HL) ; + LD ($4007),DE ; sv PPC_lo + INC HL ; + LD E,(HL) ; + INC HL ; + LD D,(HL) ; + INC HL ; + EX DE,HL ; + ADD HL,DE ; + CALL L0F46 ; routine BREAK-1 + JR C,L066C ; to NEXT-LINE + + LD HL,$4000 ; sv ERR_NR + BIT 7,(HL) ; + JR Z,L06AE ; to STOP-LINE + + LD (HL),$0C ; + +;; STOP-LINE +L06AE: BIT 7,(IY+$38) ; sv PR_CC + CALL Z,L0871 ; routine COPY-BUFF + LD BC,$0121 ; + CALL L0918 ; routine LOC-ADDR + LD A,($4000) ; sv ERR_NR + LD BC,($4007) ; sv PPC_lo + INC A ; + JR Z,L06D1 ; to REPORT + + CP $09 ; + JR NZ,L06CA ; to CONTINUE + + INC BC ; + +;; CONTINUE +L06CA: LD ($402B),BC ; sv OLDPPC_lo + JR NZ,L06D1 ; to REPORT + + DEC BC ; + +;; REPORT +L06D1: CALL L07EB ; routine OUT-CODE + LD A,$18 ; + + RST 10H ; PRINT-A + CALL L0A98 ; routine OUT-NUM + CALL L14AD ; routine CURSOR-IN + JP L04C1 ; to DISPLAY-6 + +; --- + +;; N/L-LINE +L06E0: LD ($400A),BC ; sv E_PPC_lo + LD HL,($4016) ; sv CH_ADD_lo + EX DE,HL ; + LD HL,L0413 ; Address: N/L-ONLY + PUSH HL ; + LD HL,($401A) ; sv STKBOT_lo + SBC HL,DE ; + PUSH HL ; + PUSH BC ; + CALL L02E7 ; routine SET-FAST + CALL L0A2A ; routine CLS + POP HL ; + CALL L09D8 ; routine LINE-ADDR + JR NZ,L0705 ; to COPY-OVER + + CALL L09F2 ; routine NEXT-ONE + CALL L0A60 ; routine RECLAIM-2 + +;; COPY-OVER +L0705: POP BC ; + LD A,C ; + DEC A ; + OR B ; + RET Z ; + + PUSH BC ; + INC BC ; + INC BC ; + INC BC ; + INC BC ; + DEC HL ; + CALL L099E ; routine MAKE-ROOM + CALL L0207 ; routine SLOW/FAST + POP BC ; + PUSH BC ; + INC DE ; + LD HL,($401A) ; sv STKBOT_lo + DEC HL ; + LDDR ; copy bytes + LD HL,($400A) ; sv E_PPC_lo + EX DE,HL ; + POP BC ; + LD (HL),B ; + DEC HL ; + LD (HL),C ; + DEC HL ; + LD (HL),E ; + DEC HL ; + LD (HL),D ; + + RET ; return. + +; --------------------------------------- +; THE 'LIST' AND 'LLIST' COMMAND ROUTINES +; --------------------------------------- +; +; + +;; LLIST +L072C: SET 1,(IY+$01) ; sv FLAGS - signal printer in use + +;; LIST +L0730: CALL L0EA7 ; routine FIND-INT + + LD A,B ; fetch high byte of user-supplied line number. + AND $3F ; and crudely limit to range 1-16383. + + LD H,A ; + LD L,C ; + LD ($400A),HL ; sv E_PPC_lo + CALL L09D8 ; routine LINE-ADDR + +;; LIST-PROG +L073E: LD E,$00 ; + +;; UNTIL-END +L0740: CALL L0745 ; routine OUT-LINE lists one line of BASIC + ; making an early return when the screen is + ; full or the end of program is reached. >> + JR L0740 ; loop back to UNTIL-END + +; ----------------------------------- +; THE 'PRINT A BASIC LINE' SUBROUTINE +; ----------------------------------- +; +; + +;; OUT-LINE +L0745: LD BC,($400A) ; sv E_PPC_lo + CALL L09EA ; routine CP-LINES + LD D,$92 ; + JR Z,L0755 ; to TEST-END + + LD DE,$0000 ; + RL E ; + +;; TEST-END +L0755: LD (IY+$1E),E ; sv BERG + LD A,(HL) ; + CP $40 ; + POP BC ; + RET NC ; + + PUSH BC ; + CALL L0AA5 ; routine OUT-NO + INC HL ; + LD A,D ; + + RST 10H ; PRINT-A + INC HL ; + INC HL ; + +;; COPY-LINE +L0766: LD ($4016),HL ; sv CH_ADD_lo + SET 0,(IY+$01) ; sv FLAGS - Suppress leading space + +;; MORE-LINE +L076D: LD BC,($4018) ; sv X_PTR_lo + LD HL,($4016) ; sv CH_ADD_lo + AND A ; + SBC HL,BC ; + JR NZ,L077C ; to TEST-NUM + + LD A,$B8 ; + + RST 10H ; PRINT-A + +;; TEST-NUM +L077C: LD HL,($4016) ; sv CH_ADD_lo + LD A,(HL) ; + INC HL ; + CALL L07B4 ; routine NUMBER + LD ($4016),HL ; sv CH_ADD_lo + JR Z,L076D ; to MORE-LINE + + CP $7F ; + JR Z,L079D ; to OUT-CURS + + CP $76 ; + JR Z,L07EE ; to OUT-CH + + BIT 6,A ; + JR Z,L079A ; to NOT-TOKEN + + CALL L094B ; routine TOKENS + JR L076D ; to MORE-LINE + +; --- + + +;; NOT-TOKEN +L079A: RST 10H ; PRINT-A + JR L076D ; to MORE-LINE + +; --- + +;; OUT-CURS +L079D: LD A,($4006) ; Fetch value of system variable MODE + LD B,$AB ; Prepare an inverse [F] for function cursor. + + AND A ; Test for zero - + JR NZ,L07AA ; forward if not to FLAGS-2 + + LD A,($4001) ; Fetch system variable FLAGS. + LD B,$B0 ; Prepare an inverse [K] for keyword cursor. + +;; FLAGS-2 +L07AA: RRA ; 00000?00 -> 000000?0 + RRA ; 000000?0 -> 0000000? + AND $01 ; 0000000? 0000000x + + ADD A,B ; Possibly [F] -> [G] or [K] -> [L] + + CALL L07F5 ; routine PRINT-SP prints character + JR L076D ; back to MORE-LINE + +; ----------------------- +; THE 'NUMBER' SUBROUTINE +; ----------------------- +; +; + +;; NUMBER +L07B4: CP $7E ; + RET NZ ; + + INC HL ; + INC HL ; + INC HL ; + INC HL ; + INC HL ; + RET ; + +; -------------------------------- +; THE 'KEYBOARD DECODE' SUBROUTINE +; -------------------------------- +; +; + +;; DECODE +L07BD: LD D,$00 ; + SRA B ; + SBC A,A ; + OR $26 ; + LD L,$05 ; + SUB L ; + +;; KEY-LINE +L07C7: ADD A,L ; + SCF ; Set Carry Flag + RR C ; + JR C,L07C7 ; to KEY-LINE + + INC C ; + RET NZ ; + + LD C,B ; + DEC L ; + LD L,$01 ; + JR NZ,L07C7 ; to KEY-LINE + + LD HL,$007D ; (expr reqd) + LD E,A ; + ADD HL,DE ; + SCF ; Set Carry Flag + RET ; + +; ------------------------- +; THE 'PRINTING' SUBROUTINE +; ------------------------- +; +; + +;; LEAD-SP +L07DC: LD A,E ; + AND A ; + RET M ; + + JR L07F1 ; to PRINT-CH + +; --- + +;; OUT-DIGIT +L07E1: XOR A ; + +;; DIGIT-INC +L07E2: ADD HL,BC ; + INC A ; + JR C,L07E2 ; to DIGIT-INC + + SBC HL,BC ; + DEC A ; + JR Z,L07DC ; to LEAD-SP + +;; OUT-CODE +L07EB: LD E,$1C ; + ADD A,E ; + +;; OUT-CH +L07EE: AND A ; + JR Z,L07F5 ; to PRINT-SP + +;; PRINT-CH +L07F1: RES 0,(IY+$01) ; update FLAGS - signal leading space permitted + +;; PRINT-SP +L07F5: EXX ; + PUSH HL ; + BIT 1,(IY+$01) ; test FLAGS - is printer in use ? + JR NZ,L0802 ; to LPRINT-A + + CALL L0808 ; routine ENTER-CH + JR L0805 ; to PRINT-EXX + +; --- + +;; LPRINT-A +L0802: CALL L0851 ; routine LPRINT-CH + +;; PRINT-EXX +L0805: POP HL ; + EXX ; + RET ; + +; --- + +;; ENTER-CH +L0808: LD D,A ; + LD BC,($4039) ; sv S_POSN_x + LD A,C ; + CP $21 ; + JR Z,L082C ; to TEST-LOW + +;; TEST-N/L +L0812: LD A,$76 ; + CP D ; + JR Z,L0847 ; to WRITE-N/L + + LD HL,($400E) ; sv DF_CC_lo + CP (HL) ; + LD A,D ; + JR NZ,L083E ; to WRITE-CH + + DEC C ; + JR NZ,L083A ; to EXPAND-1 + + INC HL ; + LD ($400E),HL ; sv DF_CC_lo + LD C,$21 ; + DEC B ; + LD ($4039),BC ; sv S_POSN_x + +;; TEST-LOW +L082C: LD A,B ; + CP (IY+$22) ; sv DF_SZ + JR Z,L0835 ; to REPORT-5 + + AND A ; + JR NZ,L0812 ; to TEST-N/L + +;; REPORT-5 +L0835: LD L,$04 ; 'No more room on screen' + JP L0058 ; to ERROR-3 + +; --- + +;; EXPAND-1 +L083A: CALL L099B ; routine ONE-SPACE + EX DE,HL ; + +;; WRITE-CH +L083E: LD (HL),A ; + INC HL ; + LD ($400E),HL ; sv DF_CC_lo + DEC (IY+$39) ; sv S_POSN_x + RET ; + +; --- + +;; WRITE-N/L +L0847: LD C,$21 ; + DEC B ; + SET 0,(IY+$01) ; sv FLAGS - Suppress leading space + JP L0918 ; to LOC-ADDR + +; -------------------------- +; THE 'LPRINT-CH' SUBROUTINE +; -------------------------- +; This routine sends a character to the ZX-Printer placing the code for the +; character in the Printer Buffer. +; Note. PR-CC contains the low byte of the buffer address. The high order byte +; is always constant. + + +;; LPRINT-CH +L0851: CP $76 ; compare to NEWLINE. + JR Z,L0871 ; forward if so to COPY-BUFF + + LD C,A ; take a copy of the character in C. + LD A,($4038) ; fetch print location from PR_CC + AND $7F ; ignore bit 7 to form true position. + CP $5C ; compare to 33rd location + + LD L,A ; form low-order byte. + LD H,$40 ; the high-order byte is fixed. + + CALL Z,L0871 ; routine COPY-BUFF to send full buffer to + ; the printer if first 32 bytes full. + ; (this will reset HL to start.) + + LD (HL),C ; place character at location. + INC L ; increment - will not cross a 256 boundary. + LD (IY+$38),L ; update system variable PR_CC + ; automatically resetting bit 7 to show that + ; the buffer is not empty. + RET ; return. + +; -------------------------- +; THE 'COPY' COMMAND ROUTINE +; -------------------------- +; The full character-mapped screen is copied to the ZX-Printer. +; All twenty-four text/graphic lines are printed. + +;; COPY +L0869: LD D,$16 ; prepare to copy twenty four text lines. + LD HL,($400C) ; set HL to start of display file from D_FILE. + INC HL ; + JR L0876 ; forward to COPY*D + +; --- + +; A single character-mapped printer buffer is copied to the ZX-Printer. + +;; COPY-BUFF +L0871: LD D,$01 ; prepare to copy a single text line. + LD HL,$403C ; set HL to start of printer buffer PRBUFF. + +; both paths converge here. + +;; COPY*D +L0876: CALL L02E7 ; routine SET-FAST + + PUSH BC ; *** preserve BC throughout. + ; a pending character may be present + ; in C from LPRINT-CH + +;; COPY-LOOP +L087A: PUSH HL ; save first character of line pointer. (*) + XOR A ; clear accumulator. + LD E,A ; set pixel line count, range 0-7, to zero. + +; this inner loop deals with each horizontal pixel line. + +;; COPY-TIME +L087D: OUT ($FB),A ; bit 2 reset starts the printer motor + ; with an inactive stylus - bit 7 reset. + POP HL ; pick up first character of line pointer (*) + ; on inner loop. + +;; COPY-BRK +L0880: CALL L0F46 ; routine BREAK-1 + JR C,L088A ; forward with no keypress to COPY-CONT + +; else A will hold 11111111 0 + + RRA ; 0111 1111 + OUT ($FB),A ; stop ZX printer motor, de-activate stylus. + +;; REPORT-D2 +L0888: RST 08H ; ERROR-1 + DEFB $0C ; Error Report: BREAK - CONT repeats + +; --- + +;; COPY-CONT +L088A: IN A,($FB) ; read from printer port. + ADD A,A ; test bit 6 and 7 + JP M,L08DE ; jump forward with no printer to COPY-END + + JR NC,L0880 ; back if stylus not in position to COPY-BRK + + PUSH HL ; save first character of line pointer (*) + PUSH DE ; ** preserve character line and pixel line. + + LD A,D ; text line count to A? + CP $02 ; sets carry if last line. + SBC A,A ; now $FF if last line else zero. + +; now cleverly prepare a printer control mask setting bit 2 (later moved to 1) +; of D to slow printer for the last two pixel lines ( E = 6 and 7) + + AND E ; and with pixel line offset 0-7 + RLCA ; shift to left. + AND E ; and again. + LD D,A ; store control mask in D. + +;; COPY-NEXT +L089C: LD C,(HL) ; load character from screen or buffer. + LD A,C ; save a copy in C for later inverse test. + INC HL ; update pointer for next time. + CP $76 ; is character a NEWLINE ? + JR Z,L08C7 ; forward, if so, to COPY-N/L + + PUSH HL ; * else preserve the character pointer. + + SLA A ; (?) multiply by two + ADD A,A ; multiply by four + ADD A,A ; multiply by eight + + LD H,$0F ; load H with half the address of character set. + RL H ; now $1E or $1F (with carry) + ADD A,E ; add byte offset 0-7 + LD L,A ; now HL addresses character source byte + + RL C ; test character, setting carry if inverse. + SBC A,A ; accumulator now $00 if normal, $FF if inverse. + + XOR (HL) ; combine with bit pattern at end or ROM. + LD C,A ; transfer the byte to C. + LD B,$08 ; count eight bits to output. + +;; COPY-BITS +L08B5: LD A,D ; fetch speed control mask from D. + RLC C ; rotate a bit from output byte to carry. + RRA ; pick up in bit 7, speed bit to bit 1 + LD H,A ; store aligned mask in H register. + +;; COPY-WAIT +L08BA: IN A,($FB) ; read the printer port + RRA ; test for alignment signal from encoder. + JR NC,L08BA ; loop if not present to COPY-WAIT + + LD A,H ; control byte to A. + OUT ($FB),A ; and output to printer port. + DJNZ L08B5 ; loop for all eight bits to COPY-BITS + + POP HL ; * restore character pointer. + JR L089C ; back for adjacent character line to COPY-NEXT + +; --- + +; A NEWLINE has been encountered either following a text line or as the +; first character of the screen or printer line. + +;; COPY-N/L +L08C7: IN A,($FB) ; read printer port. + RRA ; wait for encoder signal. + JR NC,L08C7 ; loop back if not to COPY-N/L + + LD A,D ; transfer speed mask to A. + RRCA ; rotate speed bit to bit 1. + ; bit 7, stylus control is reset. + OUT ($FB),A ; set the printer speed. + + POP DE ; ** restore character line and pixel line. + INC E ; increment pixel line 0-7. + BIT 3,E ; test if value eight reached. + JR Z,L087D ; back if not to COPY-TIME + +; eight pixel lines, a text line have been completed. + + POP BC ; lose the now redundant first character + ; pointer + DEC D ; decrease text line count. + JR NZ,L087A ; back if not zero to COPY-LOOP + + LD A,$04 ; stop the already slowed printer motor. + OUT ($FB),A ; output to printer port. + +;; COPY-END +L08DE: CALL L0207 ; routine SLOW/FAST + POP BC ; *** restore preserved BC. + +; ------------------------------------- +; THE 'CLEAR PRINTER BUFFER' SUBROUTINE +; ------------------------------------- +; This subroutine sets 32 bytes of the printer buffer to zero (space) and +; the 33rd character is set to a NEWLINE. +; This occurs after the printer buffer is sent to the printer but in addition +; after the 24 lines of the screen are sent to the printer. +; Note. This is a logic error as the last operation does not involve the +; buffer at all. Logically one should be able to use +; 10 LPRINT "HELLO "; +; 20 COPY +; 30 LPRINT ; "WORLD" +; and expect to see the entire greeting emerge from the printer. +; Surprisingly this logic error was never discovered and although one can argue +; if the above is a bug, the repetition of this error on the Spectrum was most +; definitely a bug. +; Since the printer buffer is fixed at the end of the system variables, and +; the print position is in the range $3C - $5C, then bit 7 of the system +; variable is set to show the buffer is empty and automatically reset when +; the variable is updated with any print position - neat. + +;; CLEAR-PRB +L08E2: LD HL,$405C ; address fixed end of PRBUFF + LD (HL),$76 ; place a newline at last position. + LD B,$20 ; prepare to blank 32 preceding characters. + +;; PRB-BYTES +L08E9: DEC HL ; decrement address - could be DEC L. + LD (HL),$00 ; place a zero byte. + DJNZ L08E9 ; loop for all thirty-two to PRB-BYTES + + LD A,L ; fetch character print position. + SET 7,A ; signal the printer buffer is clear. + LD ($4038),A ; update one-byte system variable PR_CC + RET ; return. + +; ------------------------- +; THE 'PRINT AT' SUBROUTINE +; ------------------------- +; +; + +;; PRINT-AT +L08F5: LD A,$17 ; + SUB B ; + JR C,L0905 ; to WRONG-VAL + +;; TEST-VAL +L08FA: CP (IY+$22) ; sv DF_SZ + JP C,L0835 ; to REPORT-5 + + INC A ; + LD B,A ; + LD A,$1F ; + SUB C ; + +;; WRONG-VAL +L0905: JP C,L0EAD ; to REPORT-B + + ADD A,$02 ; + LD C,A ; + +;; SET-FIELD +L090B: BIT 1,(IY+$01) ; sv FLAGS - Is printer in use + JR Z,L0918 ; to LOC-ADDR + + LD A,$5D ; + SUB C ; + LD ($4038),A ; sv PR_CC + RET ; + +; ---------------------------- +; THE 'LOCATE ADDRESS' ROUTINE +; ---------------------------- +; +; + +;; LOC-ADDR +L0918: LD ($4039),BC ; sv S_POSN_x + LD HL,($4010) ; sv VARS_lo + LD D,C ; + LD A,$22 ; + SUB C ; + LD C,A ; + LD A,$76 ; + INC B ; + +;; LOOK-BACK +L0927: DEC HL ; + CP (HL) ; + JR NZ,L0927 ; to LOOK-BACK + + DJNZ L0927 ; to LOOK-BACK + + INC HL ; + CPIR ; + DEC HL ; + LD ($400E),HL ; sv DF_CC_lo + SCF ; Set Carry Flag + RET PO ; + + DEC D ; + RET Z ; + + PUSH BC ; + CALL L099E ; routine MAKE-ROOM + POP BC ; + LD B,C ; + LD H,D ; + LD L,E ; + +;; EXPAND-2 +L0940: LD (HL),$00 ; + DEC HL ; + DJNZ L0940 ; to EXPAND-2 + + EX DE,HL ; + INC HL ; + LD ($400E),HL ; sv DF_CC_lo + RET ; + +; ------------------------------ +; THE 'EXPAND TOKENS' SUBROUTINE +; ------------------------------ +; +; + +;; TOKENS +L094B: PUSH AF ; + CALL L0975 ; routine TOKEN-ADD + JR NC,L0959 ; to ALL-CHARS + + BIT 0,(IY+$01) ; sv FLAGS - Leading space if set + JR NZ,L0959 ; to ALL-CHARS + + XOR A ; + + RST 10H ; PRINT-A + +;; ALL-CHARS +L0959: LD A,(BC) ; + AND $3F ; + + RST 10H ; PRINT-A + LD A,(BC) ; + INC BC ; + ADD A,A ; + JR NC,L0959 ; to ALL-CHARS + + POP BC ; + BIT 7,B ; + RET Z ; + + CP $1A ; + JR Z,L096D ; to TRAIL-SP + + CP $38 ; + RET C ; + +;; TRAIL-SP +L096D: XOR A ; + SET 0,(IY+$01) ; sv FLAGS - Suppress leading space + JP L07F5 ; to PRINT-SP + +; --- + +;; TOKEN-ADD +L0975: PUSH HL ; + LD HL,L0111 ; Address of TOKENS + BIT 7,A ; + JR Z,L097F ; to TEST-HIGH + + AND $3F ; + +;; TEST-HIGH +L097F: CP $43 ; + JR NC,L0993 ; to FOUND + + LD B,A ; + INC B ; + +;; WORDS +L0985: BIT 7,(HL) ; + INC HL ; + JR Z,L0985 ; to WORDS + + DJNZ L0985 ; to WORDS + + BIT 6,A ; + JR NZ,L0992 ; to COMP-FLAG + + CP $18 ; + +;; COMP-FLAG +L0992: CCF ; Complement Carry Flag + +;; FOUND +L0993: LD B,H ; + LD C,L ; + POP HL ; + RET NC ; + + LD A,(BC) ; + ADD A,$E4 ; + RET ; + +; -------------------------- +; THE 'ONE SPACE' SUBROUTINE +; -------------------------- +; +; + +;; ONE-SPACE +L099B: LD BC,$0001 ; + +; -------------------------- +; THE 'MAKE ROOM' SUBROUTINE +; -------------------------- +; +; + +;; MAKE-ROOM +L099E: PUSH HL ; + CALL L0EC5 ; routine TEST-ROOM + POP HL ; + CALL L09AD ; routine POINTERS + LD HL,($401C) ; sv STKEND_lo + EX DE,HL ; + LDDR ; Copy Bytes + RET ; + +; ------------------------- +; THE 'POINTERS' SUBROUTINE +; ------------------------- +; +; + +;; POINTERS +L09AD: PUSH AF ; + PUSH HL ; + LD HL,$400C ; sv D_FILE_lo + LD A,$09 ; + +;; NEXT-PTR +L09B4: LD E,(HL) ; + INC HL ; + LD D,(HL) ; + EX (SP),HL ; + AND A ; + SBC HL,DE ; + ADD HL,DE ; + EX (SP),HL ; + JR NC,L09C8 ; to PTR-DONE + + PUSH DE ; + EX DE,HL ; + ADD HL,BC ; + EX DE,HL ; + LD (HL),D ; + DEC HL ; + LD (HL),E ; + INC HL ; + POP DE ; + +;; PTR-DONE +L09C8: INC HL ; + DEC A ; + JR NZ,L09B4 ; to NEXT-PTR + + EX DE,HL ; + POP DE ; + POP AF ; + AND A ; + SBC HL,DE ; + LD B,H ; + LD C,L ; + INC BC ; + ADD HL,DE ; + EX DE,HL ; + RET ; + +; ----------------------------- +; THE 'LINE ADDRESS' SUBROUTINE +; ----------------------------- +; +; + +;; LINE-ADDR +L09D8: PUSH HL ; + LD HL,$407D ; + LD D,H ; + LD E,L ; + +;; NEXT-TEST +L09DE: POP BC ; + CALL L09EA ; routine CP-LINES + RET NC ; + + PUSH BC ; + CALL L09F2 ; routine NEXT-ONE + EX DE,HL ; + JR L09DE ; to NEXT-TEST + +; ------------------------------------- +; THE 'COMPARE LINE NUMBERS' SUBROUTINE +; ------------------------------------- +; +; + +;; CP-LINES +L09EA: LD A,(HL) ; + CP B ; + RET NZ ; + + INC HL ; + LD A,(HL) ; + DEC HL ; + CP C ; + RET ; + +; -------------------------------------- +; THE 'NEXT LINE OR VARIABLE' SUBROUTINE +; -------------------------------------- +; +; + +;; NEXT-ONE +L09F2: PUSH HL ; + LD A,(HL) ; + CP $40 ; + JR C,L0A0F ; to LINES + + BIT 5,A ; + JR Z,L0A10 ; forward to NEXT-O-4 + + ADD A,A ; + JP M,L0A01 ; to NEXT+FIVE + + CCF ; Complement Carry Flag + +;; NEXT+FIVE +L0A01: LD BC,$0005 ; + JR NC,L0A08 ; to NEXT-LETT + + LD C,$11 ; + +;; NEXT-LETT +L0A08: RLA ; + INC HL ; + LD A,(HL) ; + JR NC,L0A08 ; to NEXT-LETT + + JR L0A15 ; to NEXT-ADD + +; --- + +;; LINES +L0A0F: INC HL ; + +;; NEXT-O-4 +L0A10: INC HL ; + LD C,(HL) ; + INC HL ; + LD B,(HL) ; + INC HL ; + +;; NEXT-ADD +L0A15: ADD HL,BC ; + POP DE ; + +; --------------------------- +; THE 'DIFFERENCE' SUBROUTINE +; --------------------------- +; +; + +;; DIFFER +L0A17: AND A ; + SBC HL,DE ; + LD B,H ; + LD C,L ; + ADD HL,DE ; + EX DE,HL ; + RET ; + +; -------------------------- +; THE 'LINE-ENDS' SUBROUTINE +; -------------------------- +; +; + +;; LINE-ENDS +L0A1F: LD B,(IY+$22) ; sv DF_SZ + PUSH BC ; + CALL L0A2C ; routine B-LINES + POP BC ; + DEC B ; + JR L0A2C ; to B-LINES + +; ------------------------- +; THE 'CLS' COMMAND ROUTINE +; ------------------------- +; +; + +;; CLS +L0A2A: LD B,$18 ; + +;; B-LINES +L0A2C: RES 1,(IY+$01) ; sv FLAGS - Signal printer not in use + LD C,$21 ; + PUSH BC ; + CALL L0918 ; routine LOC-ADDR + POP BC ; + LD A,($4005) ; sv RAMTOP_hi + CP $4D ; + JR C,L0A52 ; to COLLAPSED + + SET 7,(IY+$3A) ; sv S_POSN_y + +;; CLEAR-LOC +L0A42: XOR A ; prepare a space + CALL L07F5 ; routine PRINT-SP prints a space + LD HL,($4039) ; sv S_POSN_x + LD A,L ; + OR H ; + AND $7E ; + JR NZ,L0A42 ; to CLEAR-LOC + + JP L0918 ; to LOC-ADDR + +; --- + +;; COLLAPSED +L0A52: LD D,H ; + LD E,L ; + DEC HL ; + LD C,B ; + LD B,$00 ; + LDIR ; Copy Bytes + LD HL,($4010) ; sv VARS_lo + +; ---------------------------- +; THE 'RECLAIMING' SUBROUTINES +; ---------------------------- +; +; + +;; RECLAIM-1 +L0A5D: CALL L0A17 ; routine DIFFER + +;; RECLAIM-2 +L0A60: PUSH BC ; + LD A,B ; + CPL ; + LD B,A ; + LD A,C ; + CPL ; + LD C,A ; + INC BC ; + CALL L09AD ; routine POINTERS + EX DE,HL ; + POP HL ; + ADD HL,DE ; + PUSH DE ; + LDIR ; Copy Bytes + POP HL ; + RET ; + +; ------------------------------ +; THE 'E-LINE NUMBER' SUBROUTINE +; ------------------------------ +; +; + +;; E-LINE-NO +L0A73: LD HL,($4014) ; sv E_LINE_lo + CALL L004D ; routine TEMP-PTR-2 + + RST 18H ; GET-CHAR + BIT 5,(IY+$2D) ; sv FLAGX + RET NZ ; + + LD HL,$405D ; sv MEM-0-1st + LD ($401C),HL ; sv STKEND_lo + CALL L1548 ; routine INT-TO-FP + CALL L158A ; routine FP-TO-BC + JR C,L0A91 ; to NO-NUMBER + + LD HL,$D8F0 ; value '-10000' + ADD HL,BC ; + +;; NO-NUMBER +L0A91: JP C,L0D9A ; to REPORT-C + + CP A ; + JP L14BC ; routine SET-MIN + +; ------------------------------------------------- +; THE 'REPORT AND LINE NUMBER' PRINTING SUBROUTINES +; ------------------------------------------------- +; +; + +;; OUT-NUM +L0A98: PUSH DE ; + PUSH HL ; + XOR A ; + BIT 7,B ; + JR NZ,L0ABF ; to UNITS + + LD H,B ; + LD L,C ; + LD E,$FF ; + JR L0AAD ; to THOUSAND + +; --- + +;; OUT-NO +L0AA5: PUSH DE ; + LD D,(HL) ; + INC HL ; + LD E,(HL) ; + PUSH HL ; + EX DE,HL ; + LD E,$00 ; set E to leading space. + +;; THOUSAND +L0AAD: LD BC,$FC18 ; + CALL L07E1 ; routine OUT-DIGIT + LD BC,$FF9C ; + CALL L07E1 ; routine OUT-DIGIT + LD C,$F6 ; + CALL L07E1 ; routine OUT-DIGIT + LD A,L ; + +;; UNITS +L0ABF: CALL L07EB ; routine OUT-CODE + POP HL ; + POP DE ; + RET ; + +; -------------------------- +; THE 'UNSTACK-Z' SUBROUTINE +; -------------------------- +; This subroutine is used to return early from a routine when checking syntax. +; On the ZX81 the same routines that execute commands also check the syntax +; on line entry. This enables precise placement of the error marker in a line +; that fails syntax. +; The sequence CALL SYNTAX-Z ; RET Z can be replaced by a call to this routine +; although it has not replaced every occurrence of the above two instructions. +; Even on the ZX-80 this routine was not fully utilized. + +;; UNSTACK-Z +L0AC5: CALL L0DA6 ; routine SYNTAX-Z resets the ZERO flag if + ; checking syntax. + POP HL ; drop the return address. + RET Z ; return to previous calling routine if + ; checking syntax. + + JP (HL) ; else jump to the continuation address in + ; the calling routine as RET would have done. + +; ---------------------------- +; THE 'LPRINT' COMMAND ROUTINE +; ---------------------------- +; +; + +;; LPRINT +L0ACB: SET 1,(IY+$01) ; sv FLAGS - Signal printer in use + +; --------------------------- +; THE 'PRINT' COMMAND ROUTINE +; --------------------------- +; +; + +;; PRINT +L0ACF: LD A,(HL) ; + CP $76 ; + JP Z,L0B84 ; to PRINT-END + +;; PRINT-1 +L0AD5: SUB $1A ; + ADC A,$00 ; + JR Z,L0B44 ; to SPACING + + CP $A7 ; + JR NZ,L0AFA ; to NOT-AT + + + RST 20H ; NEXT-CHAR + CALL L0D92 ; routine CLASS-6 + CP $1A ; + JP NZ,L0D9A ; to REPORT-C + + + RST 20H ; NEXT-CHAR + CALL L0D92 ; routine CLASS-6 + CALL L0B4E ; routine SYNTAX-ON + + RST 28H ;; FP-CALC + DEFB $01 ;;exchange + DEFB $34 ;;end-calc + + CALL L0BF5 ; routine STK-TO-BC + CALL L08F5 ; routine PRINT-AT + JR L0B37 ; to PRINT-ON + +; --- + +;; NOT-AT +L0AFA: CP $A8 ; + JR NZ,L0B31 ; to NOT-TAB + + + RST 20H ; NEXT-CHAR + CALL L0D92 ; routine CLASS-6 + CALL L0B4E ; routine SYNTAX-ON + CALL L0C02 ; routine STK-TO-A + JP NZ,L0EAD ; to REPORT-B + + AND $1F ; + LD C,A ; + BIT 1,(IY+$01) ; sv FLAGS - Is printer in use + JR Z,L0B1E ; to TAB-TEST + + SUB (IY+$38) ; sv PR_CC + SET 7,A ; + ADD A,$3C ; + CALL NC,L0871 ; routine COPY-BUFF + +;; TAB-TEST +L0B1E: ADD A,(IY+$39) ; sv S_POSN_x + CP $21 ; + LD A,($403A) ; sv S_POSN_y + SBC A,$01 ; + CALL L08FA ; routine TEST-VAL + SET 0,(IY+$01) ; sv FLAGS - Suppress leading space + JR L0B37 ; to PRINT-ON + +; --- + +;; NOT-TAB +L0B31: CALL L0F55 ; routine SCANNING + CALL L0B55 ; routine PRINT-STK + +;; PRINT-ON +L0B37: RST 18H ; GET-CHAR + SUB $1A ; + ADC A,$00 ; + JR Z,L0B44 ; to SPACING + + CALL L0D1D ; routine CHECK-END + JP L0B84 ;;; to PRINT-END + +; --- + +;; SPACING +L0B44: CALL NC,L0B8B ; routine FIELD + + RST 20H ; NEXT-CHAR + CP $76 ; + RET Z ; + + JP L0AD5 ;;; to PRINT-1 + +; --- + +;; SYNTAX-ON +L0B4E: CALL L0DA6 ; routine SYNTAX-Z + RET NZ ; + + POP HL ; + JR L0B37 ; to PRINT-ON + +; --- + +;; PRINT-STK +L0B55: CALL L0AC5 ; routine UNSTACK-Z + BIT 6,(IY+$01) ; sv FLAGS - Numeric or string result? + CALL Z,L13F8 ; routine STK-FETCH + JR Z,L0B6B ; to PR-STR-4 + + JP L15DB ; jump forward to PRINT-FP + +; --- + +;; PR-STR-1 +L0B64: LD A,$0B ; + +;; PR-STR-2 +L0B66: RST 10H ; PRINT-A + +;; PR-STR-3 +L0B67: LD DE,($4018) ; sv X_PTR_lo + +;; PR-STR-4 +L0B6B: LD A,B ; + OR C ; + DEC BC ; + RET Z ; + + LD A,(DE) ; + INC DE ; + LD ($4018),DE ; sv X_PTR_lo + BIT 6,A ; + JR Z,L0B66 ; to PR-STR-2 + + CP $C0 ; + JR Z,L0B64 ; to PR-STR-1 + + PUSH BC ; + CALL L094B ; routine TOKENS + POP BC ; + JR L0B67 ; to PR-STR-3 + +; --- + +;; PRINT-END +L0B84: CALL L0AC5 ; routine UNSTACK-Z + LD A,$76 ; + + RST 10H ; PRINT-A + RET ; + +; --- + +;; FIELD +L0B8B: CALL L0AC5 ; routine UNSTACK-Z + SET 0,(IY+$01) ; sv FLAGS - Suppress leading space + XOR A ; + + RST 10H ; PRINT-A + LD BC,($4039) ; sv S_POSN_x + LD A,C ; + BIT 1,(IY+$01) ; sv FLAGS - Is printer in use + JR Z,L0BA4 ; to CENTRE + + LD A,$5D ; + SUB (IY+$38) ; sv PR_CC + +;; CENTRE +L0BA4: LD C,$11 ; + CP C ; + JR NC,L0BAB ; to RIGHT + + LD C,$01 ; + +;; RIGHT +L0BAB: CALL L090B ; routine SET-FIELD + RET ; + +; -------------------------------------- +; THE 'PLOT AND UNPLOT' COMMAND ROUTINES +; -------------------------------------- +; +; + +;; PLOT/UNP +L0BAF: CALL L0BF5 ; routine STK-TO-BC + LD ($4036),BC ; sv COORDS_x + LD A,$2B ; + SUB B ; + JP C,L0EAD ; to REPORT-B + + LD B,A ; + LD A,$01 ; + SRA B ; + JR NC,L0BC5 ; to COLUMNS + + LD A,$04 ; + +;; COLUMNS +L0BC5: SRA C ; + JR NC,L0BCA ; to FIND-ADDR + + RLCA ; + +;; FIND-ADDR +L0BCA: PUSH AF ; + CALL L08F5 ; routine PRINT-AT + LD A,(HL) ; + RLCA ; + CP $10 ; + JR NC,L0BDA ; to TABLE-PTR + + RRCA ; + JR NC,L0BD9 ; to SQ-SAVED + + XOR $8F ; + +;; SQ-SAVED +L0BD9: LD B,A ; + +;; TABLE-PTR +L0BDA: LD DE,L0C9E ; Address: P-UNPLOT + LD A,($4030) ; sv T_ADDR_lo + SUB E ; + JP M,L0BE9 ; to PLOT + + POP AF ; + CPL ; + AND B ; + JR L0BEB ; to UNPLOT + +; --- + +;; PLOT +L0BE9: POP AF ; + OR B ; + +;; UNPLOT +L0BEB: CP $08 ; + JR C,L0BF1 ; to PLOT-END + + XOR $8F ; + +;; PLOT-END +L0BF1: EXX ; + + RST 10H ; PRINT-A + EXX ; + RET ; + +; ---------------------------- +; THE 'STACK-TO-BC' SUBROUTINE +; ---------------------------- +; +; + +;; STK-TO-BC +L0BF5: CALL L0C02 ; routine STK-TO-A + LD B,A ; + PUSH BC ; + CALL L0C02 ; routine STK-TO-A + LD E,C ; + POP BC ; + LD D,C ; + LD C,A ; + RET ; + +; --------------------------- +; THE 'STACK-TO-A' SUBROUTINE +; --------------------------- +; +; + +;; STK-TO-A +L0C02: CALL L15CD ; routine FP-TO-A + JP C,L0EAD ; to REPORT-B + + LD C,$01 ; + RET Z ; + + LD C,$FF ; + RET ; + +; ----------------------- +; THE 'SCROLL' SUBROUTINE +; ----------------------- +; +; + +;; SCROLL +L0C0E: LD B,(IY+$22) ; sv DF_SZ + LD C,$21 ; + CALL L0918 ; routine LOC-ADDR + CALL L099B ; routine ONE-SPACE + LD A,(HL) ; + LD (DE),A ; + INC (IY+$3A) ; sv S_POSN_y + LD HL,($400C) ; sv D_FILE_lo + INC HL ; + LD D,H ; + LD E,L ; + CPIR ; + JP L0A5D ; to RECLAIM-1 + +; ------------------- +; THE 'SYNTAX' TABLES +; ------------------- + +; i) The Offset table + +;; offset-t +L0C29: DEFB L0CB4 - $ ; 8B offset to; Address: P-LPRINT + DEFB L0CB7 - $ ; 8D offset to; Address: P-LLIST + DEFB L0C58 - $ ; 2D offset to; Address: P-STOP + DEFB L0CAB - $ ; 7F offset to; Address: P-SLOW + DEFB L0CAE - $ ; 81 offset to; Address: P-FAST + DEFB L0C77 - $ ; 49 offset to; Address: P-NEW + DEFB L0CA4 - $ ; 75 offset to; Address: P-SCROLL + DEFB L0C8F - $ ; 5F offset to; Address: P-CONT + DEFB L0C71 - $ ; 40 offset to; Address: P-DIM + DEFB L0C74 - $ ; 42 offset to; Address: P-REM + DEFB L0C5E - $ ; 2B offset to; Address: P-FOR + DEFB L0C4B - $ ; 17 offset to; Address: P-GOTO + DEFB L0C54 - $ ; 1F offset to; Address: P-GOSUB + DEFB L0C6D - $ ; 37 offset to; Address: P-INPUT + DEFB L0C89 - $ ; 52 offset to; Address: P-LOAD + DEFB L0C7D - $ ; 45 offset to; Address: P-LIST + DEFB L0C48 - $ ; 0F offset to; Address: P-LET + DEFB L0CA7 - $ ; 6D offset to; Address: P-PAUSE + DEFB L0C66 - $ ; 2B offset to; Address: P-NEXT + DEFB L0C80 - $ ; 44 offset to; Address: P-POKE + DEFB L0C6A - $ ; 2D offset to; Address: P-PRINT + DEFB L0C98 - $ ; 5A offset to; Address: P-PLOT + DEFB L0C7A - $ ; 3B offset to; Address: P-RUN + DEFB L0C8C - $ ; 4C offset to; Address: P-SAVE + DEFB L0C86 - $ ; 45 offset to; Address: P-RAND + DEFB L0C4F - $ ; 0D offset to; Address: P-IF + DEFB L0C95 - $ ; 52 offset to; Address: P-CLS + DEFB L0C9E - $ ; 5A offset to; Address: P-UNPLOT + DEFB L0C92 - $ ; 4D offset to; Address: P-CLEAR + DEFB L0C5B - $ ; 15 offset to; Address: P-RETURN + DEFB L0CB1 - $ ; 6A offset to; Address: P-COPY + +; ii) The parameter table. + + +;; P-LET +L0C48: DEFB $01 ; Class-01 - A variable is required. + DEFB $14 ; Separator: '=' + DEFB $02 ; Class-02 - An expression, numeric or string, + ; must follow. + +;; P-GOTO +L0C4B: DEFB $06 ; Class-06 - A numeric expression must follow. + DEFB $00 ; Class-00 - No further operands. + DEFW L0E81 ; Address: $0E81; Address: GOTO + +;; P-IF +L0C4F: DEFB $06 ; Class-06 - A numeric expression must follow. + DEFB $DE ; Separator: 'THEN' + DEFB $05 ; Class-05 - Variable syntax checked entirely + ; by routine. + DEFW L0DAB ; Address: $0DAB; Address: IF + +;; P-GOSUB +L0C54: DEFB $06 ; Class-06 - A numeric expression must follow. + DEFB $00 ; Class-00 - No further operands. + DEFW L0EB5 ; Address: $0EB5; Address: GOSUB + +;; P-STOP +L0C58: DEFB $00 ; Class-00 - No further operands. + DEFW L0CDC ; Address: $0CDC; Address: STOP + +;; P-RETURN +L0C5B: DEFB $00 ; Class-00 - No further operands. + DEFW L0ED8 ; Address: $0ED8; Address: RETURN + +;; P-FOR +L0C5E: DEFB $04 ; Class-04 - A single character variable must + ; follow. + DEFB $14 ; Separator: '=' + DEFB $06 ; Class-06 - A numeric expression must follow. + DEFB $DF ; Separator: 'TO' + DEFB $06 ; Class-06 - A numeric expression must follow. + DEFB $05 ; Class-05 - Variable syntax checked entirely + ; by routine. + DEFW L0DB9 ; Address: $0DB9; Address: FOR + +;; P-NEXT +L0C66: DEFB $04 ; Class-04 - A single character variable must + ; follow. + DEFB $00 ; Class-00 - No further operands. + DEFW L0E2E ; Address: $0E2E; Address: NEXT + +;; P-PRINT +L0C6A: DEFB $05 ; Class-05 - Variable syntax checked entirely + ; by routine. + DEFW L0ACF ; Address: $0ACF; Address: PRINT + +;; P-INPUT +L0C6D: DEFB $01 ; Class-01 - A variable is required. + DEFB $00 ; Class-00 - No further operands. + DEFW L0EE9 ; Address: $0EE9; Address: INPUT + +;; P-DIM +L0C71: DEFB $05 ; Class-05 - Variable syntax checked entirely + ; by routine. + DEFW L1409 ; Address: $1409; Address: DIM + +;; P-REM +L0C74: DEFB $05 ; Class-05 - Variable syntax checked entirely + ; by routine. + DEFW L0D6A ; Address: $0D6A; Address: REM + +;; P-NEW +L0C77: DEFB $00 ; Class-00 - No further operands. + DEFW L03C3 ; Address: $03C3; Address: NEW + +;; P-RUN +L0C7A: DEFB $03 ; Class-03 - A numeric expression may follow + ; else default to zero. + DEFW L0EAF ; Address: $0EAF; Address: RUN + +;; P-LIST +L0C7D: DEFB $03 ; Class-03 - A numeric expression may follow + ; else default to zero. + DEFW L0730 ; Address: $0730; Address: LIST + +;; P-POKE +L0C80: DEFB $06 ; Class-06 - A numeric expression must follow. + DEFB $1A ; Separator: ',' + DEFB $06 ; Class-06 - A numeric expression must follow. + DEFB $00 ; Class-00 - No further operands. + DEFW L0E92 ; Address: $0E92; Address: POKE + +;; P-RAND +L0C86: DEFB $03 ; Class-03 - A numeric expression may follow + ; else default to zero. + DEFW L0E6C ; Address: $0E6C; Address: RAND + +;; P-LOAD +L0C89: DEFB $05 ; Class-05 - Variable syntax checked entirely + ; by routine. + DEFW L0340 ; Address: $0340; Address: LOAD + +;; P-SAVE +L0C8C: DEFB $05 ; Class-05 - Variable syntax checked entirely + ; by routine. + DEFW L02F6 ; Address: $02F6; Address: SAVE + +;; P-CONT +L0C8F: DEFB $00 ; Class-00 - No further operands. + DEFW L0E7C ; Address: $0E7C; Address: CONT + +;; P-CLEAR +L0C92: DEFB $00 ; Class-00 - No further operands. + DEFW L149A ; Address: $149A; Address: CLEAR + +;; P-CLS +L0C95: DEFB $00 ; Class-00 - No further operands. + DEFW L0A2A ; Address: $0A2A; Address: CLS + +;; P-PLOT +L0C98: DEFB $06 ; Class-06 - A numeric expression must follow. + DEFB $1A ; Separator: ',' + DEFB $06 ; Class-06 - A numeric expression must follow. + DEFB $00 ; Class-00 - No further operands. + DEFW L0BAF ; Address: $0BAF; Address: PLOT/UNP + +;; P-UNPLOT +L0C9E: DEFB $06 ; Class-06 - A numeric expression must follow. + DEFB $1A ; Separator: ',' + DEFB $06 ; Class-06 - A numeric expression must follow. + DEFB $00 ; Class-00 - No further operands. + DEFW L0BAF ; Address: $0BAF; Address: PLOT/UNP + +;; P-SCROLL +L0CA4: DEFB $00 ; Class-00 - No further operands. + DEFW L0C0E ; Address: $0C0E; Address: SCROLL + +;; P-PAUSE +L0CA7: DEFB $06 ; Class-06 - A numeric expression must follow. + DEFB $00 ; Class-00 - No further operands. + DEFW L0F32 ; Address: $0F32; Address: PAUSE + +;; P-SLOW +L0CAB: DEFB $00 ; Class-00 - No further operands. + DEFW L0F2B ; Address: $0F2B; Address: SLOW + +;; P-FAST +L0CAE: DEFB $00 ; Class-00 - No further operands. + DEFW L0F23 ; Address: $0F23; Address: FAST + +;; P-COPY +L0CB1: DEFB $00 ; Class-00 - No further operands. + DEFW L0869 ; Address: $0869; Address: COPY + +;; P-LPRINT +L0CB4: DEFB $05 ; Class-05 - Variable syntax checked entirely + ; by routine. + DEFW L0ACB ; Address: $0ACB; Address: LPRINT + +;; P-LLIST +L0CB7: DEFB $03 ; Class-03 - A numeric expression may follow + ; else default to zero. + DEFW L072C ; Address: $072C; Address: LLIST + + +; --------------------------- +; THE 'LINE SCANNING' ROUTINE +; --------------------------- +; +; + +;; LINE-SCAN +L0CBA: LD (IY+$01),$01 ; sv FLAGS + CALL L0A73 ; routine E-LINE-NO + +;; LINE-RUN +L0CC1: CALL L14BC ; routine SET-MIN + LD HL,$4000 ; sv ERR_NR + LD (HL),$FF ; + LD HL,$402D ; sv FLAGX + BIT 5,(HL) ; + JR Z,L0CDE ; to LINE-NULL + + CP $E3 ; 'STOP' ? + LD A,(HL) ; + JP NZ,L0D6F ; to INPUT-REP + + CALL L0DA6 ; routine SYNTAX-Z + RET Z ; + + + RST 08H ; ERROR-1 + DEFB $0C ; Error Report: BREAK - CONT repeats + + +; -------------------------- +; THE 'STOP' COMMAND ROUTINE +; -------------------------- +; +; + +;; STOP +L0CDC: RST 08H ; ERROR-1 + DEFB $08 ; Error Report: STOP statement + +; --- + +; the interpretation of a line continues with a check for just spaces +; followed by a carriage return. +; The IF command also branches here with a true value to execute the +; statement after the THEN but the statement can be null so +; 10 IF 1 = 1 THEN +; passes syntax (on all ZX computers). + +;; LINE-NULL +L0CDE: RST 18H ; GET-CHAR + LD B,$00 ; prepare to index - early. + CP $76 ; compare to NEWLINE. + RET Z ; return if so. + + LD C,A ; transfer character to C. + + RST 20H ; NEXT-CHAR advances. + LD A,C ; character to A + SUB $E1 ; subtract 'LPRINT' - lowest command. + JR C,L0D26 ; forward if less to REPORT-C2 + + LD C,A ; reduced token to C + LD HL,L0C29 ; set HL to address of offset table. + ADD HL,BC ; index into offset table. + LD C,(HL) ; fetch offset + ADD HL,BC ; index into parameter table. + JR L0CF7 ; to GET-PARAM + +; --- + +;; SCAN-LOOP +L0CF4: LD HL,($4030) ; sv T_ADDR_lo + +; -> Entry Point to Scanning Loop + +;; GET-PARAM +L0CF7: LD A,(HL) ; + INC HL ; + LD ($4030),HL ; sv T_ADDR_lo + + LD BC,L0CF4 ; Address: SCAN-LOOP + PUSH BC ; is pushed on machine stack. + + LD C,A ; + CP $0B ; + JR NC,L0D10 ; to SEPARATOR + + LD HL,L0D16 ; class-tbl - the address of the class table. + LD B,$00 ; + ADD HL,BC ; + LD C,(HL) ; + ADD HL,BC ; + PUSH HL ; + + RST 18H ; GET-CHAR + RET ; indirect jump to class routine and + ; by subsequent RET to SCAN-LOOP. + +; ----------------------- +; THE 'SEPARATOR' ROUTINE +; ----------------------- + +;; SEPARATOR +L0D10: RST 18H ; GET-CHAR + CP C ; + JR NZ,L0D26 ; to REPORT-C2 + ; 'Nonsense in BASIC' + + RST 20H ; NEXT-CHAR + RET ; return + + +; ------------------------- +; THE 'COMMAND CLASS' TABLE +; ------------------------- +; + +;; class-tbl +L0D16: DEFB L0D2D - $ ; 17 offset to; Address: CLASS-0 + DEFB L0D3C - $ ; 25 offset to; Address: CLASS-1 + DEFB L0D6B - $ ; 53 offset to; Address: CLASS-2 + DEFB L0D28 - $ ; 0F offset to; Address: CLASS-3 + DEFB L0D85 - $ ; 6B offset to; Address: CLASS-4 + DEFB L0D2E - $ ; 13 offset to; Address: CLASS-5 + DEFB L0D92 - $ ; 76 offset to; Address: CLASS-6 + + +; -------------------------- +; THE 'CHECK END' SUBROUTINE +; -------------------------- +; Check for end of statement and that no spurious characters occur after +; a correctly parsed statement. Since only one statement is allowed on each +; line, the only character that may follow a statement is a NEWLINE. +; + +;; CHECK-END +L0D1D: CALL L0DA6 ; routine SYNTAX-Z + RET NZ ; return in runtime. + + POP BC ; else drop return address. + +;; CHECK-2 +L0D22: LD A,(HL) ; fetch character. + CP $76 ; compare to NEWLINE. + RET Z ; return if so. + +;; REPORT-C2 +L0D26: JR L0D9A ; to REPORT-C + ; 'Nonsense in BASIC' + +; -------------------------- +; COMMAND CLASSES 03, 00, 05 +; -------------------------- +; +; + +;; CLASS-3 +L0D28: CP $76 ; + CALL L0D9C ; routine NO-TO-STK + +;; CLASS-0 +L0D2D: CP A ; + +;; CLASS-5 +L0D2E: POP BC ; + CALL Z,L0D1D ; routine CHECK-END + EX DE,HL ; + LD HL,($4030) ; sv T_ADDR_lo + LD C,(HL) ; + INC HL ; + LD B,(HL) ; + EX DE,HL ; + +;; CLASS-END +L0D3A: PUSH BC ; + RET ; + +; ------------------------------ +; COMMAND CLASSES 01, 02, 04, 06 +; ------------------------------ +; +; + +;; CLASS-1 +L0D3C: CALL L111C ; routine LOOK-VARS + +;; CLASS-4-2 +L0D3F: LD (IY+$2D),$00 ; sv FLAGX + JR NC,L0D4D ; to SET-STK + + SET 1,(IY+$2D) ; sv FLAGX + JR NZ,L0D63 ; to SET-STRLN + + +;; REPORT-2 +L0D4B: RST 08H ; ERROR-1 + DEFB $01 ; Error Report: Variable not found + +; --- + +;; SET-STK +L0D4D: CALL Z,L11A7 ; routine STK-VAR + BIT 6,(IY+$01) ; sv FLAGS - Numeric or string result? + JR NZ,L0D63 ; to SET-STRLN + + XOR A ; + CALL L0DA6 ; routine SYNTAX-Z + CALL NZ,L13F8 ; routine STK-FETCH + LD HL,$402D ; sv FLAGX + OR (HL) ; + LD (HL),A ; + EX DE,HL ; + +;; SET-STRLN +L0D63: LD ($402E),BC ; sv STRLEN_lo + LD ($4012),HL ; sv DEST-lo + +; THE 'REM' COMMAND ROUTINE + +;; REM +L0D6A: RET ; + +; --- + +;; CLASS-2 +L0D6B: POP BC ; + LD A,($4001) ; sv FLAGS + +;; INPUT-REP +L0D6F: PUSH AF ; + CALL L0F55 ; routine SCANNING + POP AF ; + LD BC,L1321 ; Address: LET + LD D,(IY+$01) ; sv FLAGS + XOR D ; + AND $40 ; + JR NZ,L0D9A ; to REPORT-C + + BIT 7,D ; + JR NZ,L0D3A ; to CLASS-END + + JR L0D22 ; to CHECK-2 + +; --- + +;; CLASS-4 +L0D85: CALL L111C ; routine LOOK-VARS + PUSH AF ; + LD A,C ; + OR $9F ; + INC A ; + JR NZ,L0D9A ; to REPORT-C + + POP AF ; + JR L0D3F ; to CLASS-4-2 + +; --- + +;; CLASS-6 +L0D92: CALL L0F55 ; routine SCANNING + BIT 6,(IY+$01) ; sv FLAGS - Numeric or string result? + RET NZ ; + + +;; REPORT-C +L0D9A: RST 08H ; ERROR-1 + DEFB $0B ; Error Report: Nonsense in BASIC + +; -------------------------------- +; THE 'NUMBER TO STACK' SUBROUTINE +; -------------------------------- +; +; + +;; NO-TO-STK +L0D9C: JR NZ,L0D92 ; back to CLASS-6 with a non-zero number. + + CALL L0DA6 ; routine SYNTAX-Z + RET Z ; return if checking syntax. + +; in runtime a zero default is placed on the calculator stack. + + RST 28H ;; FP-CALC + DEFB $A0 ;;stk-zero + DEFB $34 ;;end-calc + + RET ; return. + +; ------------------------- +; THE 'SYNTAX-Z' SUBROUTINE +; ------------------------- +; This routine returns with zero flag set if checking syntax. +; Calling this routine uses three instruction bytes compared to four if the +; bit test is implemented inline. + +;; SYNTAX-Z +L0DA6: BIT 7,(IY+$01) ; test FLAGS - checking syntax only? + RET ; return. + +; ------------------------ +; THE 'IF' COMMAND ROUTINE +; ------------------------ +; In runtime, the class routines have evaluated the test expression and +; the result, true or false, is on the stack. + +;; IF +L0DAB: CALL L0DA6 ; routine SYNTAX-Z + JR Z,L0DB6 ; forward if checking syntax to IF-END + +; else delete the Boolean value on the calculator stack. + + RST 28H ;; FP-CALC + DEFB $02 ;;delete + DEFB $34 ;;end-calc + +; register DE points to exponent of floating point value. + + LD A,(DE) ; fetch exponent. + AND A ; test for zero - FALSE. + RET Z ; return if so. + +;; IF-END +L0DB6: JP L0CDE ; jump back to LINE-NULL + +; ------------------------- +; THE 'FOR' COMMAND ROUTINE +; ------------------------- +; +; + +;; FOR +L0DB9: CP $E0 ; is current character 'STEP' ? + JR NZ,L0DC6 ; forward if not to F-USE-ONE + + + RST 20H ; NEXT-CHAR + CALL L0D92 ; routine CLASS-6 stacks the number + CALL L0D1D ; routine CHECK-END + JR L0DCC ; forward to F-REORDER + +; --- + +;; F-USE-ONE +L0DC6: CALL L0D1D ; routine CHECK-END + + RST 28H ;; FP-CALC + DEFB $A1 ;;stk-one + DEFB $34 ;;end-calc + + + +;; F-REORDER +L0DCC: RST 28H ;; FP-CALC v, l, s. + DEFB $C0 ;;st-mem-0 v, l, s. + DEFB $02 ;;delete v, l. + DEFB $01 ;;exchange l, v. + DEFB $E0 ;;get-mem-0 l, v, s. + DEFB $01 ;;exchange l, s, v. + DEFB $34 ;;end-calc l, s, v. + + CALL L1321 ; routine LET + + LD ($401F),HL ; set MEM to address variable. + DEC HL ; point to letter. + LD A,(HL) ; + SET 7,(HL) ; + LD BC,$0006 ; + ADD HL,BC ; + RLCA ; + JR C,L0DEA ; to F-LMT-STP + + SLA C ; + CALL L099E ; routine MAKE-ROOM + INC HL ; + +;; F-LMT-STP +L0DEA: PUSH HL ; + + RST 28H ;; FP-CALC + DEFB $02 ;;delete + DEFB $02 ;;delete + DEFB $34 ;;end-calc + + POP HL ; + EX DE,HL ; + + LD C,$0A ; ten bytes to be moved. + LDIR ; copy bytes + + LD HL,($4007) ; set HL to system variable PPC current line. + EX DE,HL ; transfer to DE, variable pointer to HL. + INC DE ; loop start will be this line + 1 at least. + LD (HL),E ; + INC HL ; + LD (HL),D ; + CALL L0E5A ; routine NEXT-LOOP considers an initial pass. + RET NC ; return if possible. + +; else program continues from point following matching NEXT. + + BIT 7,(IY+$08) ; test PPC_hi + RET NZ ; return if over 32767 ??? + + LD B,(IY+$2E) ; fetch variable name from STRLEN_lo + RES 6,B ; make a true letter. + LD HL,($4029) ; set HL from NXTLIN + +; now enter a loop to look for matching next. + +;; NXTLIN-NO +L0E0E: LD A,(HL) ; fetch high byte of line number. + AND $C0 ; mask off low bits $3F + JR NZ,L0E2A ; forward at end of program to FOR-END + + PUSH BC ; save letter + CALL L09F2 ; routine NEXT-ONE finds next line. + POP BC ; restore letter + + INC HL ; step past low byte + INC HL ; past the + INC HL ; line length. + CALL L004C ; routine TEMP-PTR1 sets CH_ADD + + RST 18H ; GET-CHAR + CP $F3 ; compare to 'NEXT'. + EX DE,HL ; next line to HL. + JR NZ,L0E0E ; back with no match to NXTLIN-NO + +; + + EX DE,HL ; restore pointer. + + RST 20H ; NEXT-CHAR advances and gets letter in A. + EX DE,HL ; save pointer + CP B ; compare to variable name. + JR NZ,L0E0E ; back with mismatch to NXTLIN-NO + +;; FOR-END +L0E2A: LD ($4029),HL ; update system variable NXTLIN + RET ; return. + +; -------------------------- +; THE 'NEXT' COMMAND ROUTINE +; -------------------------- +; +; + +;; NEXT +L0E2E: BIT 1,(IY+$2D) ; sv FLAGX + JP NZ,L0D4B ; to REPORT-2 + + LD HL,($4012) ; DEST + BIT 7,(HL) ; + JR Z,L0E58 ; to REPORT-1 + + INC HL ; + LD ($401F),HL ; sv MEM_lo + + RST 28H ;; FP-CALC + DEFB $E0 ;;get-mem-0 + DEFB $E2 ;;get-mem-2 + DEFB $0F ;;addition + DEFB $C0 ;;st-mem-0 + DEFB $02 ;;delete + DEFB $34 ;;end-calc + + CALL L0E5A ; routine NEXT-LOOP + RET C ; + + LD HL,($401F) ; sv MEM_lo + LD DE,$000F ; + ADD HL,DE ; + LD E,(HL) ; + INC HL ; + LD D,(HL) ; + EX DE,HL ; + JR L0E86 ; to GOTO-2 + +; --- + + +;; REPORT-1 +L0E58: RST 08H ; ERROR-1 + DEFB $00 ; Error Report: NEXT without FOR + + +; -------------------------- +; THE 'NEXT-LOOP' SUBROUTINE +; -------------------------- +; +; + +;; NEXT-LOOP +L0E5A: RST 28H ;; FP-CALC + DEFB $E1 ;;get-mem-1 + DEFB $E0 ;;get-mem-0 + DEFB $E2 ;;get-mem-2 + DEFB $32 ;;less-0 + DEFB $00 ;;jump-true + DEFB $02 ;;to L0E62, LMT-V-VAL + + DEFB $01 ;;exchange + +;; LMT-V-VAL +L0E62: DEFB $03 ;;subtract + DEFB $33 ;;greater-0 + DEFB $00 ;;jump-true + DEFB $04 ;;to L0E69, IMPOSS + + DEFB $34 ;;end-calc + + AND A ; clear carry flag + RET ; return. + +; --- + + +;; IMPOSS +L0E69: DEFB $34 ;;end-calc + + SCF ; set carry flag + RET ; return. + +; -------------------------- +; THE 'RAND' COMMAND ROUTINE +; -------------------------- +; The keyword was 'RANDOMISE' on the ZX80, is 'RAND' here on the ZX81 and +; becomes 'RANDOMIZE' on the ZX Spectrum. +; In all invocations the procedure is the same - to set the SEED system variable +; with a supplied integer value or to use a time-based value if no number, or +; zero, is supplied. + +;; RAND +L0E6C: CALL L0EA7 ; routine FIND-INT + LD A,B ; test value + OR C ; for zero + JR NZ,L0E77 ; forward if not zero to SET-SEED + + LD BC,($4034) ; fetch value of FRAMES system variable. + +;; SET-SEED +L0E77: LD ($4032),BC ; update the SEED system variable. + RET ; return. + +; -------------------------- +; THE 'CONT' COMMAND ROUTINE +; -------------------------- +; Another abbreviated command. ROM space was really tight. +; CONTINUE at the line number that was set when break was pressed. +; Sometimes the current line, sometimes the next line. + +;; CONT +L0E7C: LD HL,($402B) ; set HL from system variable OLDPPC + JR L0E86 ; forward to GOTO-2 + +; -------------------------- +; THE 'GOTO' COMMAND ROUTINE +; -------------------------- +; This token also suffered from the shortage of room and there is no space +; getween GO and TO as there is on the ZX80 and ZX Spectrum. The same also +; applies to the GOSUB keyword. + +;; GOTO +L0E81: CALL L0EA7 ; routine FIND-INT + LD H,B ; + LD L,C ; + +;; GOTO-2 +L0E86: LD A,H ; + CP $F0 ; + JR NC,L0EAD ; to REPORT-B + + CALL L09D8 ; routine LINE-ADDR + LD ($4029),HL ; sv NXTLIN_lo + RET ; + +; -------------------------- +; THE 'POKE' COMMAND ROUTINE +; -------------------------- +; +; + +;; POKE +L0E92: CALL L15CD ; routine FP-TO-A + JR C,L0EAD ; forward, with overflow, to REPORT-B + + JR Z,L0E9B ; forward, if positive, to POKE-SAVE + + NEG ; negate + +;; POKE-SAVE +L0E9B: PUSH AF ; preserve value. + CALL L0EA7 ; routine FIND-INT gets address in BC + ; invoking the error routine with overflow + ; or a negative number. + POP AF ; restore value. + +; Note. the next two instructions are legacy code from the ZX80 and +; inappropriate here. + + BIT 7,(IY+$00) ; test ERR_NR - is it still $FF ? + RET Z ; return with error. + + LD (BC),A ; update the address contents. + RET ; return. + +; ----------------------------- +; THE 'FIND INTEGER' SUBROUTINE +; ----------------------------- +; +; + +;; FIND-INT +L0EA7: CALL L158A ; routine FP-TO-BC + JR C,L0EAD ; forward with overflow to REPORT-B + + RET Z ; return if positive (0-65535). + + +;; REPORT-B +L0EAD: RST 08H ; ERROR-1 + DEFB $0A ; Error Report: Integer out of range + +; ------------------------- +; THE 'RUN' COMMAND ROUTINE +; ------------------------- +; +; + +;; RUN +L0EAF: CALL L0E81 ; routine GOTO + JP L149A ; to CLEAR + +; --------------------------- +; THE 'GOSUB' COMMAND ROUTINE +; --------------------------- +; +; + +;; GOSUB +L0EB5: LD HL,($4007) ; sv PPC_lo + INC HL ; + EX (SP),HL ; + PUSH HL ; + LD ($4002),SP ; set the error stack pointer - ERR_SP + CALL L0E81 ; routine GOTO + LD BC,$0006 ; + +; -------------------------- +; THE 'TEST ROOM' SUBROUTINE +; -------------------------- +; +; + +;; TEST-ROOM +L0EC5: LD HL,($401C) ; sv STKEND_lo + ADD HL,BC ; + JR C,L0ED3 ; to REPORT-4 + + EX DE,HL ; + LD HL,$0024 ; + ADD HL,DE ; + SBC HL,SP ; + RET C ; + +;; REPORT-4 +L0ED3: LD L,$03 ; + JP L0058 ; to ERROR-3 + +; ---------------------------- +; THE 'RETURN' COMMAND ROUTINE +; ---------------------------- +; +; + +;; RETURN +L0ED8: POP HL ; + EX (SP),HL ; + LD A,H ; + CP $3E ; + JR Z,L0EE5 ; to REPORT-7 + + LD ($4002),SP ; sv ERR_SP_lo + JR L0E86 ; back to GOTO-2 + +; --- + +;; REPORT-7 +L0EE5: EX (SP),HL ; + PUSH HL ; + + RST 08H ; ERROR-1 + DEFB $06 ; Error Report: RETURN without GOSUB + +; --------------------------- +; THE 'INPUT' COMMAND ROUTINE +; --------------------------- +; +; + +;; INPUT +L0EE9: BIT 7,(IY+$08) ; sv PPC_hi + JR NZ,L0F21 ; to REPORT-8 + + CALL L14A3 ; routine X-TEMP + LD HL,$402D ; sv FLAGX + SET 5,(HL) ; + RES 6,(HL) ; + LD A,($4001) ; sv FLAGS + AND $40 ; + LD BC,$0002 ; + JR NZ,L0F05 ; to PROMPT + + LD C,$04 ; + +;; PROMPT +L0F05: OR (HL) ; + LD (HL),A ; + + RST 30H ; BC-SPACES + LD (HL),$76 ; + LD A,C ; + RRCA ; + RRCA ; + JR C,L0F14 ; to ENTER-CUR + + LD A,$0B ; + LD (DE),A ; + DEC HL ; + LD (HL),A ; + +;; ENTER-CUR +L0F14: DEC HL ; + LD (HL),$7F ; + LD HL,($4039) ; sv S_POSN_x + LD ($4030),HL ; sv T_ADDR_lo + POP HL ; + JP L0472 ; to LOWER + +; --- + +;; REPORT-8 +L0F21: RST 08H ; ERROR-1 + DEFB $07 ; Error Report: End of file + +; --------------------------- +; THE 'PAUSE' COMMAND ROUTINE +; --------------------------- +; +; + +;; FAST +L0F23: CALL L02E7 ; routine SET-FAST + RES 6,(IY+$3B) ; sv CDFLAG + RET ; return. + +; -------------------------- +; THE 'SLOW' COMMAND ROUTINE +; -------------------------- +; +; + +;; SLOW +L0F2B: SET 6,(IY+$3B) ; sv CDFLAG + JP L0207 ; to SLOW/FAST + +; --------------------------- +; THE 'PAUSE' COMMAND ROUTINE +; --------------------------- + +;; PAUSE +L0F32: CALL L0EA7 ; routine FIND-INT + CALL L02E7 ; routine SET-FAST + LD H,B ; + LD L,C ; + CALL L022D ; routine DISPLAY-P + + LD (IY+$35),$FF ; sv FRAMES_hi + + CALL L0207 ; routine SLOW/FAST + JR L0F4B ; routine DEBOUNCE + +; ---------------------- +; THE 'BREAK' SUBROUTINE +; ---------------------- +; +; + +;; BREAK-1 +L0F46: LD A,$7F ; read port $7FFE - keys B,N,M,.,SPACE. + IN A,($FE) ; + RRA ; carry will be set if space not pressed. + +; ------------------------- +; THE 'DEBOUNCE' SUBROUTINE +; ------------------------- +; +; + +;; DEBOUNCE +L0F4B: RES 0,(IY+$3B) ; update system variable CDFLAG + LD A,$FF ; + LD ($4027),A ; update system variable DEBOUNCE + RET ; return. + + +; ------------------------- +; THE 'SCANNING' SUBROUTINE +; ------------------------- +; This recursive routine is where the ZX81 gets its power. Provided there is +; enough memory it can evaluate an expression of unlimited complexity. +; Note. there is no unary plus so, as on the ZX80, PRINT +1 gives a syntax error. +; PRINT +1 works on the Spectrum but so too does PRINT + "STRING". + +;; SCANNING +L0F55: RST 18H ; GET-CHAR + LD B,$00 ; set B register to zero. + PUSH BC ; stack zero as a priority end-marker. + +;; S-LOOP-1 +L0F59: CP $40 ; compare to the 'RND' character + JR NZ,L0F8C ; forward, if not, to S-TEST-PI + +; ------------------ +; THE 'RND' FUNCTION +; ------------------ + + CALL L0DA6 ; routine SYNTAX-Z + JR Z,L0F8A ; forward if checking syntax to S-JPI-END + + LD BC,($4032) ; sv SEED_lo + CALL L1520 ; routine STACK-BC + + RST 28H ;; FP-CALC + DEFB $A1 ;;stk-one + DEFB $0F ;;addition + DEFB $30 ;;stk-data + DEFB $37 ;;Exponent: $87, Bytes: 1 + DEFB $16 ;;(+00,+00,+00) + DEFB $04 ;;multiply + DEFB $30 ;;stk-data + DEFB $80 ;;Bytes: 3 + DEFB $41 ;;Exponent $91 + DEFB $00,$00,$80 ;;(+00) + DEFB $2E ;;n-mod-m + DEFB $02 ;;delete + DEFB $A1 ;;stk-one + DEFB $03 ;;subtract + DEFB $2D ;;duplicate + DEFB $34 ;;end-calc + + CALL L158A ; routine FP-TO-BC + LD ($4032),BC ; update the SEED system variable. + LD A,(HL) ; HL addresses the exponent of the last value. + AND A ; test for zero + JR Z,L0F8A ; forward, if so, to S-JPI-END + + SUB $10 ; else reduce exponent by sixteen + LD (HL),A ; thus dividing by 65536 for last value. + +;; S-JPI-END +L0F8A: JR L0F99 ; forward to S-PI-END + +; --- + +;; S-TEST-PI +L0F8C: CP $42 ; the 'PI' character + JR NZ,L0F9D ; forward, if not, to S-TST-INK + +; ------------------- +; THE 'PI' EVALUATION +; ------------------- + + CALL L0DA6 ; routine SYNTAX-Z + JR Z,L0F99 ; forward if checking syntax to S-PI-END + + + RST 28H ;; FP-CALC + DEFB $A3 ;;stk-pi/2 + DEFB $34 ;;end-calc + + INC (HL) ; double the exponent giving PI on the stack. + +;; S-PI-END +L0F99: RST 20H ; NEXT-CHAR advances character pointer. + + JP L1083 ; jump forward to S-NUMERIC to set the flag + ; to signal numeric result before advancing. + +; --- + +;; S-TST-INK +L0F9D: CP $41 ; compare to character 'INKEY$' + JR NZ,L0FB2 ; forward, if not, to S-ALPHANUM + +; ----------------------- +; THE 'INKEY$' EVALUATION +; ----------------------- + + CALL L02BB ; routine KEYBOARD + LD B,H ; + LD C,L ; + LD D,C ; + INC D ; + CALL NZ,L07BD ; routine DECODE + LD A,D ; + ADC A,D ; + LD B,D ; + LD C,A ; + EX DE,HL ; + JR L0FED ; forward to S-STRING + +; --- + +;; S-ALPHANUM +L0FB2: CALL L14D2 ; routine ALPHANUM + JR C,L1025 ; forward, if alphanumeric to S-LTR-DGT + + CP $1B ; is character a '.' ? + JP Z,L1047 ; jump forward if so to S-DECIMAL + + LD BC,$09D8 ; prepare priority 09, operation 'subtract' + CP $16 ; is character unary minus '-' ? + JR Z,L1020 ; forward, if so, to S-PUSH-PO + + CP $10 ; is character a '(' ? + JR NZ,L0FD6 ; forward if not to S-QUOTE + + CALL L0049 ; routine CH-ADD+1 advances character pointer. + + CALL L0F55 ; recursively call routine SCANNING to + ; evaluate the sub-expression. + + CP $11 ; is subsequent character a ')' ? + JR NZ,L0FFF ; forward if not to S-RPT-C + + + CALL L0049 ; routine CH-ADD+1 advances. + JR L0FF8 ; relative jump to S-JP-CONT3 and then S-CONT3 + +; --- + +; consider a quoted string e.g. PRINT "Hooray!" +; Note. quotes are not allowed within a string. + +;; S-QUOTE +L0FD6: CP $0B ; is character a quote (") ? + JR NZ,L1002 ; forward, if not, to S-FUNCTION + + CALL L0049 ; routine CH-ADD+1 advances + PUSH HL ; * save start of string. + JR L0FE3 ; forward to S-QUOTE-S + +; --- + + +;; S-Q-AGAIN +L0FE0: CALL L0049 ; routine CH-ADD+1 + +;; S-QUOTE-S +L0FE3: CP $0B ; is character a '"' ? + JR NZ,L0FFB ; forward if not to S-Q-NL + + POP DE ; * retrieve start of string + AND A ; prepare to subtract. + SBC HL,DE ; subtract start from current position. + LD B,H ; transfer this length + LD C,L ; to the BC register pair. + +;; S-STRING +L0FED: LD HL,$4001 ; address system variable FLAGS + RES 6,(HL) ; signal string result + BIT 7,(HL) ; test if checking syntax. + + CALL NZ,L12C3 ; in run-time routine STK-STO-$ stacks the + ; string descriptor - start DE, length BC. + + RST 20H ; NEXT-CHAR advances pointer. + +;; S-J-CONT-3 +L0FF8: JP L1088 ; jump to S-CONT-3 + +; --- + +; A string with no terminating quote has to be considered. + +;; S-Q-NL +L0FFB: CP $76 ; compare to NEWLINE + JR NZ,L0FE0 ; loop back if not to S-Q-AGAIN + +;; S-RPT-C +L0FFF: JP L0D9A ; to REPORT-C + +; --- + +;; S-FUNCTION +L1002: SUB $C4 ; subtract 'CODE' reducing codes + ; CODE thru '<>' to range $00 - $XX + JR C,L0FFF ; back, if less, to S-RPT-C + +; test for NOT the last function in character set. + + LD BC,$04EC ; prepare priority $04, operation 'not' + CP $13 ; compare to 'NOT' ( - CODE) + JR Z,L1020 ; forward, if so, to S-PUSH-PO + + JR NC,L0FFF ; back with anything higher to S-RPT-C + +; else is a function 'CODE' thru 'CHR$' + + LD B,$10 ; priority sixteen binds all functions to + ; arguments removing the need for brackets. + + ADD A,$D9 ; add $D9 to give range $D9 thru $EB + ; bit 6 is set to show numeric argument. + ; bit 7 is set to show numeric result. + +; now adjust these default argument/result indicators. + + LD C,A ; save code in C + + CP $DC ; separate 'CODE', 'VAL', 'LEN' + JR NC,L101A ; skip forward if string operand to S-NO-TO-$ + + RES 6,C ; signal string operand. + +;; S-NO-TO-$ +L101A: CP $EA ; isolate top of range 'STR$' and 'CHR$' + JR C,L1020 ; skip forward with others to S-PUSH-PO + + RES 7,C ; signal string result. + +;; S-PUSH-PO +L1020: PUSH BC ; push the priority/operation + + RST 20H ; NEXT-CHAR + JP L0F59 ; jump back to S-LOOP-1 + +; --- + +;; S-LTR-DGT +L1025: CP $26 ; compare to 'A'. + JR C,L1047 ; forward if less to S-DECIMAL + + CALL L111C ; routine LOOK-VARS + JP C,L0D4B ; back if not found to REPORT-2 + ; a variable is always 'found' when checking + ; syntax. + + CALL Z,L11A7 ; routine STK-VAR stacks string parameters or + ; returns cell location if numeric. + + LD A,($4001) ; fetch FLAGS + CP $C0 ; compare to numeric result/numeric operand + JR C,L1087 ; forward if not numeric to S-CONT-2 + + INC HL ; address numeric contents of variable. + LD DE,($401C) ; set destination to STKEND + CALL L19F6 ; routine MOVE-FP stacks the five bytes + EX DE,HL ; transfer new free location from DE to HL. + LD ($401C),HL ; update STKEND system variable. + JR L1087 ; forward to S-CONT-2 + +; --- + +; The Scanning Decimal routine is invoked when a decimal point or digit is +; found in the expression. +; When checking syntax, then the 'hidden floating point' form is placed +; after the number in the BASIC line. +; In run-time, the digits are skipped and the floating point number is picked +; up. + +;; S-DECIMAL +L1047: CALL L0DA6 ; routine SYNTAX-Z + JR NZ,L106F ; forward in run-time to S-STK-DEC + + CALL L14D9 ; routine DEC-TO-FP + + RST 18H ; GET-CHAR advances HL past digits + LD BC,$0006 ; six locations are required. + CALL L099E ; routine MAKE-ROOM + INC HL ; point to first new location + LD (HL),$7E ; insert the number marker 126 decimal. + INC HL ; increment + EX DE,HL ; transfer destination to DE. + LD HL,($401C) ; set HL from STKEND which points to the + ; first location after the 'last value' + LD C,$05 ; five bytes to move. + AND A ; clear carry. + SBC HL,BC ; subtract five pointing to 'last value'. + LD ($401C),HL ; update STKEND thereby 'deleting the value. + + LDIR ; copy the five value bytes. + + EX DE,HL ; basic pointer to HL which may be white-space + ; following the number. + DEC HL ; now points to last of five bytes. + CALL L004C ; routine TEMP-PTR1 advances the character + ; address skipping any white-space. + JR L1083 ; forward to S-NUMERIC + ; to signal a numeric result. + +; --- + +; In run-time the branch is here when a digit or point is encountered. + +;; S-STK-DEC +L106F: RST 20H ; NEXT-CHAR + CP $7E ; compare to 'number marker' + JR NZ,L106F ; loop back until found to S-STK-DEC + ; skipping all the digits. + + INC HL ; point to first of five hidden bytes. + LD DE,($401C) ; set destination from STKEND system variable + CALL L19F6 ; routine MOVE-FP stacks the number. + LD ($401C),DE ; update system variable STKEND. + LD ($4016),HL ; update system variable CH_ADD. + +;; S-NUMERIC +L1083: SET 6,(IY+$01) ; update FLAGS - Signal numeric result + +;; S-CONT-2 +L1087: RST 18H ; GET-CHAR + +;; S-CONT-3 +L1088: CP $10 ; compare to opening bracket '(' + JR NZ,L1098 ; forward if not to S-OPERTR + + BIT 6,(IY+$01) ; test FLAGS - Numeric or string result? + JR NZ,L10BC ; forward if numeric to S-LOOP + +; else is a string + + CALL L1263 ; routine SLICING + + RST 20H ; NEXT-CHAR + JR L1088 ; back to S-CONT-3 + +; --- + +; the character is now manipulated to form an equivalent in the table of +; calculator literals. This is quite cumbersome and in the ZX Spectrum a +; simple look-up table was introduced at this point. + +;; S-OPERTR +L1098: LD BC,$00C3 ; prepare operator 'subtract' as default. + ; also set B to zero for later indexing. + + CP $12 ; is character '>' ? + JR C,L10BC ; forward if less to S-LOOP as + ; we have reached end of meaningful expression + + SUB $16 ; is character '-' ? + JR NC,L10A7 ; forward with - * / and '**' '<>' to SUBMLTDIV + + ADD A,$0D ; increase others by thirteen + ; $09 '>' thru $0C '+' + JR L10B5 ; forward to GET-PRIO + +; --- + +;; SUBMLTDIV +L10A7: CP $03 ; isolate $00 '-', $01 '*', $02 '/' + JR C,L10B5 ; forward if so to GET-PRIO + +; else possibly originally $D8 '**' thru $DD '<>' already reduced by $16 + + SUB $C2 ; giving range $00 to $05 + JR C,L10BC ; forward if less to S-LOOP + + CP $06 ; test the upper limit for nonsense also + JR NC,L10BC ; forward if so to S-LOOP + + ADD A,$03 ; increase by 3 to give combined operators of + + ; $00 '-' + ; $01 '*' + ; $02 '/' + + ; $03 '**' + ; $04 'OR' + ; $05 'AND' + ; $06 '<=' + ; $07 '>=' + ; $08 '<>' + + ; $09 '>' + ; $0A '<' + ; $0B '=' + ; $0C '+' + +;; GET-PRIO +L10B5: ADD A,C ; add to default operation 'sub' ($C3) + LD C,A ; and place in operator byte - C. + + LD HL,L110F - $C3 ; theoretical base of the priorities table. + ADD HL,BC ; add C ( B is zero) + LD B,(HL) ; pick up the priority in B + +;; S-LOOP +L10BC: POP DE ; restore previous + LD A,D ; load A with priority. + CP B ; is present priority higher + JR C,L10ED ; forward if so to S-TIGHTER + + AND A ; are both priorities zero + JP Z,L0018 ; exit if zero via GET-CHAR + + PUSH BC ; stack present values + PUSH DE ; stack last values + CALL L0DA6 ; routine SYNTAX-Z + JR Z,L10D5 ; forward is checking syntax to S-SYNTEST + + LD A,E ; fetch last operation + AND $3F ; mask off the indicator bits to give true + ; calculator literal. + LD B,A ; place in the B register for BREG + +; perform the single operation + + RST 28H ;; FP-CALC + DEFB $37 ;;fp-calc-2 + DEFB $34 ;;end-calc + + JR L10DE ; forward to S-RUNTEST + +; --- + +;; S-SYNTEST +L10D5: LD A,E ; transfer masked operator to A + XOR (IY+$01) ; XOR with FLAGS like results will reset bit 6 + AND $40 ; test bit 6 + +;; S-RPORT-C +L10DB: JP NZ,L0D9A ; back to REPORT-C if results do not agree. + +; --- + +; in run-time impose bit 7 of the operator onto bit 6 of the FLAGS + +;; S-RUNTEST +L10DE: POP DE ; restore last operation. + LD HL,$4001 ; address system variable FLAGS + SET 6,(HL) ; presume a numeric result + BIT 7,E ; test expected result in operation + JR NZ,L10EA ; forward if numeric to S-LOOPEND + + RES 6,(HL) ; reset to signal string result + +;; S-LOOPEND +L10EA: POP BC ; restore present values + JR L10BC ; back to S-LOOP + +; --- + +;; S-TIGHTER +L10ED: PUSH DE ; push last values and consider these + + LD A,C ; get the present operator. + BIT 6,(IY+$01) ; test FLAGS - Numeric or string result? + JR NZ,L110A ; forward if numeric to S-NEXT + + AND $3F ; strip indicator bits to give clear literal. + ADD A,$08 ; add eight - augmenting numeric to equivalent + ; string literals. + LD C,A ; place plain literal back in C. + CP $10 ; compare to 'AND' + JR NZ,L1102 ; forward if not to S-NOT-AND + + SET 6,C ; set the numeric operand required for 'AND' + JR L110A ; forward to S-NEXT + +; --- + +;; S-NOT-AND +L1102: JR C,L10DB ; back if less than 'AND' to S-RPORT-C + ; Nonsense if '-', '*' etc. + + CP $17 ; compare to 'strs-add' literal + JR Z,L110A ; forward if so signaling string result + + SET 7,C ; set bit to numeric (Boolean) for others. + +;; S-NEXT +L110A: PUSH BC ; stack 'present' values + + RST 20H ; NEXT-CHAR + JP L0F59 ; jump back to S-LOOP-1 + + + +; ------------------------- +; THE 'TABLE OF PRIORITIES' +; ------------------------- +; +; + +;; tbl-pri +L110F: DEFB $06 ; '-' + DEFB $08 ; '*' + DEFB $08 ; '/' + DEFB $0A ; '**' + DEFB $02 ; 'OR' + DEFB $03 ; 'AND' + DEFB $05 ; '<=' + DEFB $05 ; '>=' + DEFB $05 ; '<>' + DEFB $05 ; '>' + DEFB $05 ; '<' + DEFB $05 ; '=' + DEFB $06 ; '+' + + +; -------------------------- +; THE 'LOOK-VARS' SUBROUTINE +; -------------------------- +; +; + +;; LOOK-VARS +L111C: SET 6,(IY+$01) ; sv FLAGS - Signal numeric result + + RST 18H ; GET-CHAR + CALL L14CE ; routine ALPHA + JP NC,L0D9A ; to REPORT-C + + PUSH HL ; + LD C,A ; + + RST 20H ; NEXT-CHAR + PUSH HL ; + RES 5,C ; + CP $10 ; + JR Z,L1148 ; to V-SYN/RUN + + SET 6,C ; + CP $0D ; + JR Z,L1143 ; forward to V-STR-VAR + + SET 5,C ; + +;; V-CHAR +L1139: CALL L14D2 ; routine ALPHANUM + JR NC,L1148 ; forward when not to V-RUN/SYN + + RES 6,C ; + + RST 20H ; NEXT-CHAR + JR L1139 ; loop back to V-CHAR + +; --- + +;; V-STR-VAR +L1143: RST 20H ; NEXT-CHAR + RES 6,(IY+$01) ; sv FLAGS - Signal string result + +;; V-RUN/SYN +L1148: LD B,C ; + CALL L0DA6 ; routine SYNTAX-Z + JR NZ,L1156 ; forward to V-RUN + + LD A,C ; + AND $E0 ; + SET 7,A ; + LD C,A ; + JR L118A ; forward to V-SYNTAX + +; --- + +;; V-RUN +L1156: LD HL,($4010) ; sv VARS + +;; V-EACH +L1159: LD A,(HL) ; + AND $7F ; + JR Z,L1188 ; to V-80-BYTE + + CP C ; + JR NZ,L1180 ; to V-NEXT + + RLA ; + ADD A,A ; + JP P,L1195 ; to V-FOUND-2 + + JR C,L1195 ; to V-FOUND-2 + + POP DE ; + PUSH DE ; + PUSH HL ; + +;; V-MATCHES +L116B: INC HL ; + +;; V-SPACES +L116C: LD A,(DE) ; + INC DE ; + AND A ; + JR Z,L116C ; back to V-SPACES + + CP (HL) ; + JR Z,L116B ; back to V-MATCHES + + OR $80 ; + CP (HL) ; + JR NZ,L117F ; forward to V-GET-PTR + + LD A,(DE) ; + CALL L14D2 ; routine ALPHANUM + JR NC,L1194 ; forward to V-FOUND-1 + +;; V-GET-PTR +L117F: POP HL ; + +;; V-NEXT +L1180: PUSH BC ; + CALL L09F2 ; routine NEXT-ONE + EX DE,HL ; + POP BC ; + JR L1159 ; back to V-EACH + +; --- + +;; V-80-BYTE +L1188: SET 7,B ; + +;; V-SYNTAX +L118A: POP DE ; + + RST 18H ; GET-CHAR + CP $10 ; + JR Z,L1199 ; forward to V-PASS + + SET 5,B ; + JR L11A1 ; forward to V-END + +; --- + +;; V-FOUND-1 +L1194: POP DE ; + +;; V-FOUND-2 +L1195: POP DE ; + POP DE ; + PUSH HL ; + + RST 18H ; GET-CHAR + +;; V-PASS +L1199: CALL L14D2 ; routine ALPHANUM + JR NC,L11A1 ; forward if not alphanumeric to V-END + + + RST 20H ; NEXT-CHAR + JR L1199 ; back to V-PASS + +; --- + +;; V-END +L11A1: POP HL ; + RL B ; + BIT 6,B ; + RET ; + +; ------------------------ +; THE 'STK-VAR' SUBROUTINE +; ------------------------ +; +; + +;; STK-VAR +L11A7: XOR A ; + LD B,A ; + BIT 7,C ; + JR NZ,L11F8 ; forward to SV-COUNT + + BIT 7,(HL) ; + JR NZ,L11BF ; forward to SV-ARRAYS + + INC A ; + +;; SV-SIMPLE$ +L11B2: INC HL ; + LD C,(HL) ; + INC HL ; + LD B,(HL) ; + INC HL ; + EX DE,HL ; + CALL L12C3 ; routine STK-STO-$ + + RST 18H ; GET-CHAR + JP L125A ; jump forward to SV-SLICE? + +; --- + +;; SV-ARRAYS +L11BF: INC HL ; + INC HL ; + INC HL ; + LD B,(HL) ; + BIT 6,C ; + JR Z,L11D1 ; forward to SV-PTR + + DEC B ; + JR Z,L11B2 ; forward to SV-SIMPLE$ + + EX DE,HL ; + + RST 18H ; GET-CHAR + CP $10 ; + JR NZ,L1231 ; forward to REPORT-3 + + EX DE,HL ; + +;; SV-PTR +L11D1: EX DE,HL ; + JR L11F8 ; forward to SV-COUNT + +; --- + +;; SV-COMMA +L11D4: PUSH HL ; + + RST 18H ; GET-CHAR + POP HL ; + CP $1A ; + JR Z,L11FB ; forward to SV-LOOP + + BIT 7,C ; + JR Z,L1231 ; forward to REPORT-3 + + BIT 6,C ; + JR NZ,L11E9 ; forward to SV-CLOSE + + CP $11 ; + JR NZ,L1223 ; forward to SV-RPT-C + + + RST 20H ; NEXT-CHAR + RET ; + +; --- + +;; SV-CLOSE +L11E9: CP $11 ; + JR Z,L1259 ; forward to SV-DIM + + CP $DF ; + JR NZ,L1223 ; forward to SV-RPT-C + + +;; SV-CH-ADD +L11F1: RST 18H ; GET-CHAR + DEC HL ; + LD ($4016),HL ; sv CH_ADD + JR L1256 ; forward to SV-SLICE + +; --- + +;; SV-COUNT +L11F8: LD HL,$0000 ; + +;; SV-LOOP +L11FB: PUSH HL ; + + RST 20H ; NEXT-CHAR + POP HL ; + LD A,C ; + CP $C0 ; + JR NZ,L120C ; forward to SV-MULT + + + RST 18H ; GET-CHAR + CP $11 ; + JR Z,L1259 ; forward to SV-DIM + + CP $DF ; + JR Z,L11F1 ; back to SV-CH-ADD + +;; SV-MULT +L120C: PUSH BC ; + PUSH HL ; + CALL L12FF ; routine DE,(DE+1) + EX (SP),HL ; + EX DE,HL ; + CALL L12DD ; routine INT-EXP1 + JR C,L1231 ; forward to REPORT-3 + + DEC BC ; + CALL L1305 ; routine GET-HL*DE + ADD HL,BC ; + POP DE ; + POP BC ; + DJNZ L11D4 ; loop back to SV-COMMA + + BIT 7,C ; + +;; SV-RPT-C +L1223: JR NZ,L128B ; relative jump to SL-RPT-C + + PUSH HL ; + BIT 6,C ; + JR NZ,L123D ; forward to SV-ELEM$ + + LD B,D ; + LD C,E ; + + RST 18H ; GET-CHAR + CP $11 ; is character a ')' ? + JR Z,L1233 ; skip forward to SV-NUMBER + + +;; REPORT-3 +L1231: RST 08H ; ERROR-1 + DEFB $02 ; Error Report: Subscript wrong + + +;; SV-NUMBER +L1233: RST 20H ; NEXT-CHAR + POP HL ; + LD DE,$0005 ; + CALL L1305 ; routine GET-HL*DE + ADD HL,BC ; + RET ; return >> + +; --- + +;; SV-ELEM$ +L123D: CALL L12FF ; routine DE,(DE+1) + EX (SP),HL ; + CALL L1305 ; routine GET-HL*DE + POP BC ; + ADD HL,BC ; + INC HL ; + LD B,D ; + LD C,E ; + EX DE,HL ; + CALL L12C2 ; routine STK-ST-0 + + RST 18H ; GET-CHAR + CP $11 ; is it ')' ? + JR Z,L1259 ; forward if so to SV-DIM + + CP $1A ; is it ',' ? + JR NZ,L1231 ; back if not to REPORT-3 + +;; SV-SLICE +L1256: CALL L1263 ; routine SLICING + +;; SV-DIM +L1259: RST 20H ; NEXT-CHAR + +;; SV-SLICE? +L125A: CP $10 ; + JR Z,L1256 ; back to SV-SLICE + + RES 6,(IY+$01) ; sv FLAGS - Signal string result + RET ; return. + +; ------------------------ +; THE 'SLICING' SUBROUTINE +; ------------------------ +; +; + +;; SLICING +L1263: CALL L0DA6 ; routine SYNTAX-Z + CALL NZ,L13F8 ; routine STK-FETCH + + RST 20H ; NEXT-CHAR + CP $11 ; is it ')' ? + JR Z,L12BE ; forward if so to SL-STORE + + PUSH DE ; + XOR A ; + PUSH AF ; + PUSH BC ; + LD DE,$0001 ; + + RST 18H ; GET-CHAR + POP HL ; + CP $DF ; is it 'TO' ? + JR Z,L1292 ; forward if so to SL-SECOND + + POP AF ; + CALL L12DE ; routine INT-EXP2 + PUSH AF ; + LD D,B ; + LD E,C ; + PUSH HL ; + + RST 18H ; GET-CHAR + POP HL ; + CP $DF ; is it 'TO' ? + JR Z,L1292 ; forward if so to SL-SECOND + + CP $11 ; + +;; SL-RPT-C +L128B: JP NZ,L0D9A ; to REPORT-C + + LD H,D ; + LD L,E ; + JR L12A5 ; forward to SL-DEFINE + +; --- + +;; SL-SECOND +L1292: PUSH HL ; + + RST 20H ; NEXT-CHAR + POP HL ; + CP $11 ; is it ')' ? + JR Z,L12A5 ; forward if so to SL-DEFINE + + POP AF ; + CALL L12DE ; routine INT-EXP2 + PUSH AF ; + + RST 18H ; GET-CHAR + LD H,B ; + LD L,C ; + CP $11 ; is it ')' ? + JR NZ,L128B ; back if not to SL-RPT-C + +;; SL-DEFINE +L12A5: POP AF ; + EX (SP),HL ; + ADD HL,DE ; + DEC HL ; + EX (SP),HL ; + AND A ; + SBC HL,DE ; + LD BC,$0000 ; + JR C,L12B9 ; forward to SL-OVER + + INC HL ; + AND A ; + JP M,L1231 ; jump back to REPORT-3 + + LD B,H ; + LD C,L ; + +;; SL-OVER +L12B9: POP DE ; + RES 6,(IY+$01) ; sv FLAGS - Signal string result + +;; SL-STORE +L12BE: CALL L0DA6 ; routine SYNTAX-Z + RET Z ; return if checking syntax. + +; -------------------------- +; THE 'STK-STORE' SUBROUTINE +; -------------------------- +; +; + +;; STK-ST-0 +L12C2: XOR A ; + +;; STK-STO-$ +L12C3: PUSH BC ; + CALL L19EB ; routine TEST-5-SP + POP BC ; + LD HL,($401C) ; sv STKEND + LD (HL),A ; + INC HL ; + LD (HL),E ; + INC HL ; + LD (HL),D ; + INC HL ; + LD (HL),C ; + INC HL ; + LD (HL),B ; + INC HL ; + LD ($401C),HL ; sv STKEND + RES 6,(IY+$01) ; update FLAGS - signal string result + RET ; return. + +; ------------------------- +; THE 'INT EXP' SUBROUTINES +; ------------------------- +; +; + +;; INT-EXP1 +L12DD: XOR A ; + +;; INT-EXP2 +L12DE: PUSH DE ; + PUSH HL ; + PUSH AF ; + CALL L0D92 ; routine CLASS-6 + POP AF ; + CALL L0DA6 ; routine SYNTAX-Z + JR Z,L12FC ; forward if checking syntax to I-RESTORE + + PUSH AF ; + CALL L0EA7 ; routine FIND-INT + POP DE ; + LD A,B ; + OR C ; + SCF ; Set Carry Flag + JR Z,L12F9 ; forward to I-CARRY + + POP HL ; + PUSH HL ; + AND A ; + SBC HL,BC ; + +;; I-CARRY +L12F9: LD A,D ; + SBC A,$00 ; + +;; I-RESTORE +L12FC: POP HL ; + POP DE ; + RET ; + +; -------------------------- +; THE 'DE,(DE+1)' SUBROUTINE +; -------------------------- +; INDEX and LOAD Z80 subroutine. +; This emulates the 6800 processor instruction LDX 1,X which loads a two-byte +; value from memory into the register indexing it. Often these are hardly worth +; the bother of writing as subroutines and this one doesn't save any time or +; memory. The timing and space overheads have to be offset against the ease of +; writing and the greater program readability from using such toolkit routines. + +;; DE,(DE+1) +L12FF: EX DE,HL ; move index address into HL. + INC HL ; increment to address word. + LD E,(HL) ; pick up word low-order byte. + INC HL ; index high-order byte and + LD D,(HL) ; pick it up. + RET ; return with DE = word. + +; -------------------------- +; THE 'GET-HL*DE' SUBROUTINE +; -------------------------- +; + +;; GET-HL*DE +L1305: CALL L0DA6 ; routine SYNTAX-Z + RET Z ; + + PUSH BC ; + LD B,$10 ; + LD A,H ; + LD C,L ; + LD HL,$0000 ; + +;; HL-LOOP +L1311: ADD HL,HL ; + JR C,L131A ; forward with carry to HL-END + + RL C ; + RLA ; + JR NC,L131D ; forward with no carry to HL-AGAIN + + ADD HL,DE ; + +;; HL-END +L131A: JP C,L0ED3 ; to REPORT-4 + +;; HL-AGAIN +L131D: DJNZ L1311 ; loop back to HL-LOOP + + POP BC ; + RET ; return. + +; -------------------- +; THE 'LET' SUBROUTINE +; -------------------- +; +; + +;; LET +L1321: LD HL,($4012) ; sv DEST-lo + BIT 1,(IY+$2D) ; sv FLAGX + JR Z,L136E ; forward to L-EXISTS + + LD BC,$0005 ; + +;; L-EACH-CH +L132D: INC BC ; + +; check + +;; L-NO-SP +L132E: INC HL ; + LD A,(HL) ; + AND A ; + JR Z,L132E ; back to L-NO-SP + + CALL L14D2 ; routine ALPHANUM + JR C,L132D ; back to L-EACH-CH + + CP $0D ; is it '$' ? + JP Z,L13C8 ; forward if so to L-NEW$ + + + RST 30H ; BC-SPACES + PUSH DE ; + LD HL,($4012) ; sv DEST + DEC DE ; + LD A,C ; + SUB $06 ; + LD B,A ; + LD A,$40 ; + JR Z,L1359 ; forward to L-SINGLE + +;; L-CHAR +L134B: INC HL ; + LD A,(HL) ; + AND A ; is it a space ? + JR Z,L134B ; back to L-CHAR + + INC DE ; + LD (DE),A ; + DJNZ L134B ; loop back to L-CHAR + + OR $80 ; + LD (DE),A ; + LD A,$80 ; + +;; L-SINGLE +L1359: LD HL,($4012) ; sv DEST-lo + XOR (HL) ; + POP HL ; + CALL L13E7 ; routine L-FIRST + +;; L-NUMERIC +L1361: PUSH HL ; + + RST 28H ;; FP-CALC + DEFB $02 ;;delete + DEFB $34 ;;end-calc + + POP HL ; + LD BC,$0005 ; + AND A ; + SBC HL,BC ; + JR L13AE ; forward to L-ENTER + +; --- + +;; L-EXISTS +L136E: BIT 6,(IY+$01) ; sv FLAGS - Numeric or string result? + JR Z,L137A ; forward to L-DELETE$ + + LD DE,$0006 ; + ADD HL,DE ; + JR L1361 ; back to L-NUMERIC + +; --- + +;; L-DELETE$ +L137A: LD HL,($4012) ; sv DEST-lo + LD BC,($402E) ; sv STRLEN_lo + BIT 0,(IY+$2D) ; sv FLAGX + JR NZ,L13B7 ; forward to L-ADD$ + + LD A,B ; + OR C ; + RET Z ; + + PUSH HL ; + + RST 30H ; BC-SPACES + PUSH DE ; + PUSH BC ; + LD D,H ; + LD E,L ; + INC HL ; + LD (HL),$00 ; + LDDR ; Copy Bytes + PUSH HL ; + CALL L13F8 ; routine STK-FETCH + POP HL ; + EX (SP),HL ; + AND A ; + SBC HL,BC ; + ADD HL,BC ; + JR NC,L13A3 ; forward to L-LENGTH + + LD B,H ; + LD C,L ; + +;; L-LENGTH +L13A3: EX (SP),HL ; + EX DE,HL ; + LD A,B ; + OR C ; + JR Z,L13AB ; forward if zero to L-IN-W/S + + LDIR ; Copy Bytes + +;; L-IN-W/S +L13AB: POP BC ; + POP DE ; + POP HL ; + +; ------------------------ +; THE 'L-ENTER' SUBROUTINE +; ------------------------ +; + +;; L-ENTER +L13AE: EX DE,HL ; + LD A,B ; + OR C ; + RET Z ; + + PUSH DE ; + LDIR ; Copy Bytes + POP HL ; + RET ; return. + +; --- + +;; L-ADD$ +L13B7: DEC HL ; + DEC HL ; + DEC HL ; + LD A,(HL) ; + PUSH HL ; + PUSH BC ; + + CALL L13CE ; routine L-STRING + + POP BC ; + POP HL ; + INC BC ; + INC BC ; + INC BC ; + JP L0A60 ; jump back to exit via RECLAIM-2 + +; --- + +;; L-NEW$ +L13C8: LD A,$60 ; prepare mask %01100000 + LD HL,($4012) ; sv DEST-lo + XOR (HL) ; + +; ------------------------- +; THE 'L-STRING' SUBROUTINE +; ------------------------- +; + +;; L-STRING +L13CE: PUSH AF ; + CALL L13F8 ; routine STK-FETCH + EX DE,HL ; + ADD HL,BC ; + PUSH HL ; + INC BC ; + INC BC ; + INC BC ; + + RST 30H ; BC-SPACES + EX DE,HL ; + POP HL ; + DEC BC ; + DEC BC ; + PUSH BC ; + LDDR ; Copy Bytes + EX DE,HL ; + POP BC ; + DEC BC ; + LD (HL),B ; + DEC HL ; + LD (HL),C ; + POP AF ; + +;; L-FIRST +L13E7: PUSH AF ; + CALL L14C7 ; routine REC-V80 + POP AF ; + DEC HL ; + LD (HL),A ; + LD HL,($401A) ; sv STKBOT_lo + LD ($4014),HL ; sv E_LINE_lo + DEC HL ; + LD (HL),$80 ; + RET ; + +; -------------------------- +; THE 'STK-FETCH' SUBROUTINE +; -------------------------- +; This routine fetches a five-byte value from the calculator stack +; reducing the pointer to the end of the stack by five. +; For a floating-point number the exponent is in A and the mantissa +; is the thirty-two bits EDCB. +; For strings, the start of the string is in DE and the length in BC. +; A is unused. + +;; STK-FETCH +L13F8: LD HL,($401C) ; load HL from system variable STKEND + + DEC HL ; + LD B,(HL) ; + DEC HL ; + LD C,(HL) ; + DEC HL ; + LD D,(HL) ; + DEC HL ; + LD E,(HL) ; + DEC HL ; + LD A,(HL) ; + + LD ($401C),HL ; set system variable STKEND to lower value. + RET ; return. + +; ------------------------- +; THE 'DIM' COMMAND ROUTINE +; ------------------------- +; An array is created and initialized to zeros which is also the space +; character on the ZX81. + +;; DIM +L1409: CALL L111C ; routine LOOK-VARS + +;; D-RPORT-C +L140C: JP NZ,L0D9A ; to REPORT-C + + CALL L0DA6 ; routine SYNTAX-Z + JR NZ,L141C ; forward to D-RUN + + RES 6,C ; + CALL L11A7 ; routine STK-VAR + CALL L0D1D ; routine CHECK-END + +;; D-RUN +L141C: JR C,L1426 ; forward to D-LETTER + + PUSH BC ; + CALL L09F2 ; routine NEXT-ONE + CALL L0A60 ; routine RECLAIM-2 + POP BC ; + +;; D-LETTER +L1426: SET 7,C ; + LD B,$00 ; + PUSH BC ; + LD HL,$0001 ; + BIT 6,C ; + JR NZ,L1434 ; forward to D-SIZE + + LD L,$05 ; + +;; D-SIZE +L1434: EX DE,HL ; + +;; D-NO-LOOP +L1435: RST 20H ; NEXT-CHAR + LD H,$40 ; + CALL L12DD ; routine INT-EXP1 + JP C,L1231 ; jump back to REPORT-3 + + POP HL ; + PUSH BC ; + INC H ; + PUSH HL ; + LD H,B ; + LD L,C ; + CALL L1305 ; routine GET-HL*DE + EX DE,HL ; + + RST 18H ; GET-CHAR + CP $1A ; + JR Z,L1435 ; back to D-NO-LOOP + + CP $11 ; is it ')' ? + JR NZ,L140C ; back if not to D-RPORT-C + + + RST 20H ; NEXT-CHAR + POP BC ; + LD A,C ; + LD L,B ; + LD H,$00 ; + INC HL ; + INC HL ; + ADD HL,HL ; + ADD HL,DE ; + JP C,L0ED3 ; jump to REPORT-4 + + PUSH DE ; + PUSH BC ; + PUSH HL ; + LD B,H ; + LD C,L ; + LD HL,($4014) ; sv E_LINE_lo + DEC HL ; + CALL L099E ; routine MAKE-ROOM + INC HL ; + LD (HL),A ; + POP BC ; + DEC BC ; + DEC BC ; + DEC BC ; + INC HL ; + LD (HL),C ; + INC HL ; + LD (HL),B ; + POP AF ; + INC HL ; + LD (HL),A ; + LD H,D ; + LD L,E ; + DEC DE ; + LD (HL),$00 ; + POP BC ; + LDDR ; Copy Bytes + +;; DIM-SIZES +L147F: POP BC ; + LD (HL),B ; + DEC HL ; + LD (HL),C ; + DEC HL ; + DEC A ; + JR NZ,L147F ; back to DIM-SIZES + + RET ; return. + +; --------------------- +; THE 'RESERVE' ROUTINE +; --------------------- +; +; + +;; RESERVE +L1488: LD HL,($401A) ; address STKBOT + DEC HL ; now last byte of workspace + CALL L099E ; routine MAKE-ROOM + INC HL ; + INC HL ; + POP BC ; + LD ($4014),BC ; sv E_LINE_lo + POP BC ; + EX DE,HL ; + INC HL ; + RET ; + +; --------------------------- +; THE 'CLEAR' COMMAND ROUTINE +; --------------------------- +; +; + +;; CLEAR +L149A: LD HL,($4010) ; sv VARS_lo + LD (HL),$80 ; + INC HL ; + LD ($4014),HL ; sv E_LINE_lo + +; ----------------------- +; THE 'X-TEMP' SUBROUTINE +; ----------------------- +; +; + +;; X-TEMP +L14A3: LD HL,($4014) ; sv E_LINE_lo + +; ---------------------- +; THE 'SET-STK' ROUTINES +; ---------------------- +; +; + +;; SET-STK-B +L14A6: LD ($401A),HL ; sv STKBOT + +; + +;; SET-STK-E +L14A9: LD ($401C),HL ; sv STKEND + RET ; + +; ----------------------- +; THE 'CURSOR-IN' ROUTINE +; ----------------------- +; This routine is called to set the edit line to the minimum cursor/newline +; and to set STKEND, the start of free space, at the next position. + +;; CURSOR-IN +L14AD: LD HL,($4014) ; fetch start of edit line from E_LINE + LD (HL),$7F ; insert cursor character + + INC HL ; point to next location. + LD (HL),$76 ; insert NEWLINE character + INC HL ; point to next free location. + + LD (IY+$22),$02 ; set lower screen display file size DF_SZ + + JR L14A6 ; exit via SET-STK-B above + +; ------------------------ +; THE 'SET-MIN' SUBROUTINE +; ------------------------ +; +; + +;; SET-MIN +L14BC: LD HL,$405D ; normal location of calculator's memory area + LD ($401F),HL ; update system variable MEM + LD HL,($401A) ; fetch STKBOT + JR L14A9 ; back to SET-STK-E + + +; ------------------------------------ +; THE 'RECLAIM THE END-MARKER' ROUTINE +; ------------------------------------ + +;; REC-V80 +L14C7: LD DE,($4014) ; sv E_LINE_lo + JP L0A5D ; to RECLAIM-1 + +; ---------------------- +; THE 'ALPHA' SUBROUTINE +; ---------------------- + +;; ALPHA +L14CE: CP $26 ; + JR L14D4 ; skip forward to ALPHA-2 + + +; ------------------------- +; THE 'ALPHANUM' SUBROUTINE +; ------------------------- + +;; ALPHANUM +L14D2: CP $1C ; + + +;; ALPHA-2 +L14D4: CCF ; Complement Carry Flag + RET NC ; + + CP $40 ; + RET ; + + +; ------------------------------------------ +; THE 'DECIMAL TO FLOATING POINT' SUBROUTINE +; ------------------------------------------ +; + +;; DEC-TO-FP +L14D9: CALL L1548 ; routine INT-TO-FP gets first part + CP $1B ; is character a '.' ? + JR NZ,L14F5 ; forward if not to E-FORMAT + + + RST 28H ;; FP-CALC + DEFB $A1 ;;stk-one + DEFB $C0 ;;st-mem-0 + DEFB $02 ;;delete + DEFB $34 ;;end-calc + + +;; NXT-DGT-1 +L14E5: RST 20H ; NEXT-CHAR + CALL L1514 ; routine STK-DIGIT + JR C,L14F5 ; forward to E-FORMAT + + + RST 28H ;; FP-CALC + DEFB $E0 ;;get-mem-0 + DEFB $A4 ;;stk-ten + DEFB $05 ;;division + DEFB $C0 ;;st-mem-0 + DEFB $04 ;;multiply + DEFB $0F ;;addition + DEFB $34 ;;end-calc + + JR L14E5 ; loop back till exhausted to NXT-DGT-1 + +; --- + +;; E-FORMAT +L14F5: CP $2A ; is character 'E' ? + RET NZ ; return if not + + LD (IY+$5D),$FF ; initialize sv MEM-0-1st to $FF TRUE + + RST 20H ; NEXT-CHAR + CP $15 ; is character a '+' ? + JR Z,L1508 ; forward if so to SIGN-DONE + + CP $16 ; is it a '-' ? + JR NZ,L1509 ; forward if not to ST-E-PART + + INC (IY+$5D) ; sv MEM-0-1st change to FALSE + +;; SIGN-DONE +L1508: RST 20H ; NEXT-CHAR + +;; ST-E-PART +L1509: CALL L1548 ; routine INT-TO-FP + + RST 28H ;; FP-CALC m, e. + DEFB $E0 ;;get-mem-0 m, e, (1/0) TRUE/FALSE + DEFB $00 ;;jump-true + DEFB $02 ;;to L1511, E-POSTVE + DEFB $18 ;;neg m, -e + +;; E-POSTVE +L1511: DEFB $38 ;;e-to-fp x. + DEFB $34 ;;end-calc x. + + RET ; return. + + +; -------------------------- +; THE 'STK-DIGIT' SUBROUTINE +; -------------------------- +; + +;; STK-DIGIT +L1514: CP $1C ; + RET C ; + + CP $26 ; + CCF ; Complement Carry Flag + RET C ; + + SUB $1C ; + +; ------------------------ +; THE 'STACK-A' SUBROUTINE +; ------------------------ +; + + +;; STACK-A +L151D: LD C,A ; + LD B,$00 ; + +; ------------------------- +; THE 'STACK-BC' SUBROUTINE +; ------------------------- +; The ZX81 does not have an integer number format so the BC register contents +; must be converted to their full floating-point form. + +;; STACK-BC +L1520: LD IY,$4000 ; re-initialize the system variables pointer. + PUSH BC ; save the integer value. + +; now stack zero, five zero bytes as a starting point. + + RST 28H ;; FP-CALC + DEFB $A0 ;;stk-zero 0. + DEFB $34 ;;end-calc + + POP BC ; restore integer value. + + LD (HL),$91 ; place $91 in exponent 65536. + ; this is the maximum possible value + + LD A,B ; fetch hi-byte. + AND A ; test for zero. + JR NZ,L1536 ; forward if not zero to STK-BC-2 + + LD (HL),A ; else make exponent zero again + OR C ; test lo-byte + RET Z ; return if BC was zero - done. + +; else there has to be a set bit if only the value one. + + LD B,C ; save C in B. + LD C,(HL) ; fetch zero to C + LD (HL),$89 ; make exponent $89 256. + +;; STK-BC-2 +L1536: DEC (HL) ; decrement exponent - halving number + SLA C ; C<-76543210<-0 + RL B ; C<-76543210<-C + JR NC,L1536 ; loop back if no carry to STK-BC-2 + + SRL B ; 0->76543210->C + RR C ; C->76543210->C + + INC HL ; address first byte of mantissa + LD (HL),B ; insert B + INC HL ; address second byte of mantissa + LD (HL),C ; insert C + + DEC HL ; point to the + DEC HL ; exponent again + RET ; return. + +; ------------------------------------------ +; THE 'INTEGER TO FLOATING POINT' SUBROUTINE +; ------------------------------------------ +; +; + +;; INT-TO-FP +L1548: PUSH AF ; + + RST 28H ;; FP-CALC + DEFB $A0 ;;stk-zero + DEFB $34 ;;end-calc + + POP AF ; + +;; NXT-DGT-2 +L154D: CALL L1514 ; routine STK-DIGIT + RET C ; + + + RST 28H ;; FP-CALC + DEFB $01 ;;exchange + DEFB $A4 ;;stk-ten + DEFB $04 ;;multiply + DEFB $0F ;;addition + DEFB $34 ;;end-calc + + + RST 20H ; NEXT-CHAR + JR L154D ; to NXT-DGT-2 + + +; ------------------------------------------- +; THE 'E-FORMAT TO FLOATING POINT' SUBROUTINE +; ------------------------------------------- +; (Offset $38: 'e-to-fp') +; invoked from DEC-TO-FP and PRINT-FP. +; e.g. 2.3E4 is 23000. +; This subroutine evaluates xEm where m is a positive or negative integer. +; At a simple level x is multiplied by ten for every unit of m. +; If the decimal exponent m is negative then x is divided by ten for each unit. +; A short-cut is taken if the exponent is greater than seven and in this +; case the exponent is reduced by seven and the value is multiplied or divided +; by ten million. +; Note. for the ZX Spectrum an even cleverer method was adopted which involved +; shifting the bits out of the exponent so the result was achieved with six +; shifts at most. The routine below had to be completely re-written mostly +; in Z80 machine code. +; Although no longer operable, the calculator literal was retained for old +; times sake, the routine being invoked directly from a machine code CALL. +; +; On entry in the ZX81, m, the exponent, is the 'last value', and the +; floating-point decimal mantissa is beneath it. + + +;; e-to-fp +L155A: RST 28H ;; FP-CALC x, m. + DEFB $2D ;;duplicate x, m, m. + DEFB $32 ;;less-0 x, m, (1/0). + DEFB $C0 ;;st-mem-0 x, m, (1/0). + DEFB $02 ;;delete x, m. + DEFB $27 ;;abs x, +m. + +;; E-LOOP +L1560: DEFB $A1 ;;stk-one x, m,1. + DEFB $03 ;;subtract x, m-1. + DEFB $2D ;;duplicate x, m-1,m-1. + DEFB $32 ;;less-0 x, m-1, (1/0). + DEFB $00 ;;jump-true x, m-1. + DEFB $22 ;;to L1587, E-END x, m-1. + + DEFB $2D ;;duplicate x, m-1, m-1. + DEFB $30 ;;stk-data + DEFB $33 ;;Exponent: $83, Bytes: 1 + + DEFB $40 ;;(+00,+00,+00) x, m-1, m-1, 6. + DEFB $03 ;;subtract x, m-1, m-7. + DEFB $2D ;;duplicate x, m-1, m-7, m-7. + DEFB $32 ;;less-0 x, m-1, m-7, (1/0). + DEFB $00 ;;jump-true x, m-1, m-7. + DEFB $0C ;;to L157A, E-LOW + +; but if exponent m is higher than 7 do a bigger chunk. +; multiplying (or dividing if negative) by 10 million - 1e7. + + DEFB $01 ;;exchange x, m-7, m-1. + DEFB $02 ;;delete x, m-7. + DEFB $01 ;;exchange m-7, x. + DEFB $30 ;;stk-data + DEFB $80 ;;Bytes: 3 + DEFB $48 ;;Exponent $98 + DEFB $18,$96,$80 ;;(+00) m-7, x, 10,000,000 (=f) + DEFB $2F ;;jump + DEFB $04 ;;to L157D, E-CHUNK + +; --- + +;; E-LOW +L157A: DEFB $02 ;;delete x, m-1. + DEFB $01 ;;exchange m-1, x. + DEFB $A4 ;;stk-ten m-1, x, 10 (=f). + +;; E-CHUNK +L157D: DEFB $E0 ;;get-mem-0 m-1, x, f, (1/0) + DEFB $00 ;;jump-true m-1, x, f + DEFB $04 ;;to L1583, E-DIVSN + + DEFB $04 ;;multiply m-1, x*f. + DEFB $2F ;;jump + DEFB $02 ;;to L1584, E-SWAP + +; --- + +;; E-DIVSN +L1583: DEFB $05 ;;division m-1, x/f (= new x). + +;; E-SWAP +L1584: DEFB $01 ;;exchange x, m-1 (= new m). + DEFB $2F ;;jump x, m. + DEFB $DA ;;to L1560, E-LOOP + +; --- + +;; E-END +L1587: DEFB $02 ;;delete x. (-1) + DEFB $34 ;;end-calc x. + + RET ; return. + +; ------------------------------------- +; THE 'FLOATING-POINT TO BC' SUBROUTINE +; ------------------------------------- +; The floating-point form on the calculator stack is compressed directly into +; the BC register rounding up if necessary. +; Valid range is 0 to 65535.4999 + +;; FP-TO-BC +L158A: CALL L13F8 ; routine STK-FETCH - exponent to A + ; mantissa to EDCB. + AND A ; test for value zero. + JR NZ,L1595 ; forward if not to FPBC-NZRO + +; else value is zero + + LD B,A ; zero to B + LD C,A ; also to C + PUSH AF ; save the flags on machine stack + JR L15C6 ; forward to FPBC-END + +; --- + +; EDCB => BCE + +;; FPBC-NZRO +L1595: LD B,E ; transfer the mantissa from EDCB + LD E,C ; to BCE. Bit 7 of E is the 17th bit which + LD C,D ; will be significant for rounding if the + ; number is already normalized. + + SUB $91 ; subtract 65536 + CCF ; complement carry flag + BIT 7,B ; test sign bit + PUSH AF ; push the result + + SET 7,B ; set the implied bit + JR C,L15C6 ; forward with carry from SUB/CCF to FPBC-END + ; number is too big. + + INC A ; increment the exponent and + NEG ; negate to make range $00 - $0F + + CP $08 ; test if one or two bytes + JR C,L15AF ; forward with two to BIG-INT + + LD E,C ; shift mantissa + LD C,B ; 8 places right + LD B,$00 ; insert a zero in B + SUB $08 ; reduce exponent by eight + +;; BIG-INT +L15AF: AND A ; test the exponent + LD D,A ; save exponent in D. + + LD A,E ; fractional bits to A + RLCA ; rotate most significant bit to carry for + ; rounding of an already normal number. + + JR Z,L15BC ; forward if exponent zero to EXP-ZERO + ; the number is normalized + +;; FPBC-NORM +L15B5: SRL B ; 0->76543210->C + RR C ; C->76543210->C + + DEC D ; decrement exponent + + JR NZ,L15B5 ; loop back till zero to FPBC-NORM + +;; EXP-ZERO +L15BC: JR NC,L15C6 ; forward without carry to NO-ROUND + + INC BC ; round up. + LD A,B ; test result + OR C ; for zero + JR NZ,L15C6 ; forward if not to GRE-ZERO + + POP AF ; restore sign flag + SCF ; set carry flag to indicate overflow + PUSH AF ; save combined flags again + +;; FPBC-END +L15C6: PUSH BC ; save BC value + +; set HL and DE to calculator stack pointers. + + RST 28H ;; FP-CALC + DEFB $34 ;;end-calc + + + POP BC ; restore BC value + POP AF ; restore flags + LD A,C ; copy low byte to A also. + RET ; return + +; ------------------------------------ +; THE 'FLOATING-POINT TO A' SUBROUTINE +; ------------------------------------ +; +; + +;; FP-TO-A +L15CD: CALL L158A ; routine FP-TO-BC + RET C ; + + PUSH AF ; + DEC B ; + INC B ; + JR Z,L15D9 ; forward if in range to FP-A-END + + POP AF ; fetch result + SCF ; set carry flag signaling overflow + RET ; return + +;; FP-A-END +L15D9: POP AF ; + RET ; + + +; ---------------------------------------------- +; THE 'PRINT A FLOATING-POINT NUMBER' SUBROUTINE +; ---------------------------------------------- +; prints 'last value' x on calculator stack. +; There are a wide variety of formats see Chapter 4. +; e.g. +; PI prints as 3.1415927 +; .123 prints as 0.123 +; .0123 prints as .0123 +; 999999999999 prints as 1000000000000 +; 9876543210123 prints as 9876543200000 + +; Begin by isolating zero and just printing the '0' character +; for that case. For negative numbers print a leading '-' and +; then form the absolute value of x. + +;; PRINT-FP +L15DB: RST 28H ;; FP-CALC x. + DEFB $2D ;;duplicate x, x. + DEFB $32 ;;less-0 x, (1/0). + DEFB $00 ;;jump-true + DEFB $0B ;;to L15EA, PF-NGTVE x. + + DEFB $2D ;;duplicate x, x + DEFB $33 ;;greater-0 x, (1/0). + DEFB $00 ;;jump-true + DEFB $0D ;;to L15F0, PF-POSTVE x. + + DEFB $02 ;;delete . + DEFB $34 ;;end-calc . + + LD A,$1C ; load accumulator with character '0' + + RST 10H ; PRINT-A + RET ; return. >> + +; --- + +;; PF-NEGTVE +L15EA: DEFB $27 ; abs +x. + DEFB $34 ;;end-calc x. + + LD A,$16 ; load accumulator with '-' + + RST 10H ; PRINT-A + + RST 28H ;; FP-CALC x. + +;; PF-POSTVE +L15F0: DEFB $34 ;;end-calc x. + +; register HL addresses the exponent of the floating-point value. +; if positive, and point floats to left, then bit 7 is set. + + LD A,(HL) ; pick up the exponent byte + CALL L151D ; routine STACK-A places on calculator stack. + +; now calculate roughly the number of digits, n, before the decimal point by +; subtracting a half from true exponent and multiplying by log to +; the base 10 of 2. +; The true number could be one higher than n, the integer result. + + RST 28H ;; FP-CALC x, e. + DEFB $30 ;;stk-data + DEFB $78 ;;Exponent: $88, Bytes: 2 + DEFB $00,$80 ;;(+00,+00) x, e, 128.5. + DEFB $03 ;;subtract x, e -.5. + DEFB $30 ;;stk-data + DEFB $EF ;;Exponent: $7F, Bytes: 4 + DEFB $1A,$20,$9A,$85 ;; .30103 (log10 2) + DEFB $04 ;;multiply x, + DEFB $24 ;;int + DEFB $C1 ;;st-mem-1 x, n. + + + DEFB $30 ;;stk-data + DEFB $34 ;;Exponent: $84, Bytes: 1 + DEFB $00 ;;(+00,+00,+00) x, n, 8. + + DEFB $03 ;;subtract x, n-8. + DEFB $18 ;;neg x, 8-n. + DEFB $38 ;;e-to-fp x * (10^n) + +; finally the 8 or 9 digit decimal is rounded. +; a ten-digit integer can arise in the case of, say, 999999999.5 +; which gives 1000000000. + + DEFB $A2 ;;stk-half + DEFB $0F ;;addition + DEFB $24 ;;int i. + DEFB $34 ;;end-calc + +; If there were 8 digits then final rounding will take place on the calculator +; stack above and the next two instructions insert a masked zero so that +; no further rounding occurs. If the result is a 9 digit integer then +; rounding takes place within the buffer. + + LD HL,$406B ; address system variable MEM-2-5th + ; which could be the 'ninth' digit. + LD (HL),$90 ; insert the value $90 10010000 + +; now starting from lowest digit lay down the 8, 9 or 10 digit integer +; which represents the significant portion of the number +; e.g. PI will be the nine-digit integer 314159265 + + LD B,$0A ; count is ten digits. + +;; PF-LOOP +L1615: INC HL ; increase pointer + + PUSH HL ; preserve buffer address. + PUSH BC ; preserve counter. + + RST 28H ;; FP-CALC i. + DEFB $A4 ;;stk-ten i, 10. + DEFB $2E ;;n-mod-m i mod 10, i/10 + DEFB $01 ;;exchange i/10, remainder. + DEFB $34 ;;end-calc + + CALL L15CD ; routine FP-TO-A $00-$09 + + OR $90 ; make left hand nibble 9 + + POP BC ; restore counter + POP HL ; restore buffer address. + + LD (HL),A ; insert masked digit in buffer. + DJNZ L1615 ; loop back for all ten to PF-LOOP + +; the most significant digit will be last but if the number is exhausted then +; the last one or two positions will contain zero ($90). + +; e.g. for 'one' we have zero as estimate of leading digits. +; 1*10^8 100000000 as integer value +; 90 90 90 90 90 90 90 90 91 90 as buffer mem3/mem4 contents. + + + INC HL ; advance pointer to one past buffer + LD BC,$0008 ; set C to 8 ( B is already zero ) + PUSH HL ; save pointer. + +;; PF-NULL +L162C: DEC HL ; decrease pointer + LD A,(HL) ; fetch masked digit + CP $90 ; is it a leading zero ? + JR Z,L162C ; loop back if so to PF-NULL + +; at this point a significant digit has been found. carry is reset. + + SBC HL,BC ; subtract eight from the address. + PUSH HL ; ** save this pointer too + LD A,(HL) ; fetch addressed byte + ADD A,$6B ; add $6B - forcing a round up ripple + ; if $95 or over. + PUSH AF ; save the carry result. + +; now enter a loop to round the number. After rounding has been considered +; a zero that has arisen from rounding or that was present at that position +; originally is changed from $90 to $80. + +;; PF-RND-LP +L1639: POP AF ; retrieve carry from machine stack. + INC HL ; increment address + LD A,(HL) ; fetch new byte + ADC A,$00 ; add in any carry + + DAA ; decimal adjust accumulator + ; carry will ripple through the '9' + + PUSH AF ; save carry on machine stack. + AND $0F ; isolate character 0 - 9 AND set zero flag + ; if zero. + LD (HL),A ; place back in location. + SET 7,(HL) ; set bit 7 to show printable. + ; but not if trailing zero after decimal point. + JR Z,L1639 ; back if a zero to PF-RND-LP + ; to consider further rounding and/or trailing + ; zero identification. + + POP AF ; balance stack + POP HL ; ** retrieve lower pointer + +; now insert 6 trailing zeros which are printed if before the decimal point +; but mark the end of printing if after decimal point. +; e.g. 9876543210123 is printed as 9876543200000 +; 123.456001 is printed as 123.456 + + LD B,$06 ; the count is six. + +;; PF-ZERO-6 +L164B: LD (HL),$80 ; insert a masked zero + DEC HL ; decrease pointer. + DJNZ L164B ; loop back for all six to PF-ZERO-6 + +; n-mod-m reduced the number to zero and this is now deleted from the calculator +; stack before fetching the original estimate of leading digits. + + + RST 28H ;; FP-CALC 0. + DEFB $02 ;;delete . + DEFB $E1 ;;get-mem-1 n. + DEFB $34 ;;end-calc n. + + CALL L15CD ; routine FP-TO-A + JR Z,L165B ; skip forward if positive to PF-POS + + NEG ; negate makes positive + +;; PF-POS +L165B: LD E,A ; transfer count of digits to E + INC E ; increment twice + INC E ; + POP HL ; * retrieve pointer to one past buffer. + +;; GET-FIRST +L165F: DEC HL ; decrement address. + DEC E ; decrement digit counter. + LD A,(HL) ; fetch masked byte. + AND $0F ; isolate right-hand nibble. + JR Z,L165F ; back with leading zero to GET-FIRST + +; now determine if E-format printing is needed + + LD A,E ; transfer now accurate number count to A. + SUB $05 ; subtract five + CP $08 ; compare with 8 as maximum digits is 13. + JP P,L1682 ; forward if positive to PF-E-FMT + + CP $F6 ; test for more than four zeros after point. + JP M,L1682 ; forward if so to PF-E-FMT + + ADD A,$06 ; test for zero leading digits, e.g. 0.5 + JR Z,L16BF ; forward if so to PF-ZERO-1 + + JP M,L16B2 ; forward if more than one zero to PF-ZEROS + +; else digits before the decimal point are to be printed + + LD B,A ; count of leading characters to B. + +;; PF-NIB-LP +L167B: CALL L16D0 ; routine PF-NIBBLE + DJNZ L167B ; loop back for counted numbers to PF-NIB-LP + + JR L16C2 ; forward to consider decimal part to PF-DC-OUT + +; --- + +;; PF-E-FMT +L1682: LD B,E ; count to B + CALL L16D0 ; routine PF-NIBBLE prints one digit. + CALL L16C2 ; routine PF-DC-OUT considers fractional part. + + LD A,$2A ; prepare character 'E' + RST 10H ; PRINT-A + + LD A,B ; transfer exponent to A + AND A ; test the sign. + JP P,L1698 ; forward if positive to PF-E-POS + + NEG ; negate the negative exponent. + LD B,A ; save positive exponent in B. + + LD A,$16 ; prepare character '-' + JR L169A ; skip forward to PF-E-SIGN + +; --- + +;; PF-E-POS +L1698: LD A,$15 ; prepare character '+' + +;; PF-E-SIGN +L169A: RST 10H ; PRINT-A + +; now convert the integer exponent in B to two characters. +; it will be less than 99. + + LD A,B ; fetch positive exponent. + LD B,$FF ; initialize left hand digit to minus one. + +;; PF-E-TENS +L169E: INC B ; increment ten count + SUB $0A ; subtract ten from exponent + JR NC,L169E ; loop back if greater than ten to PF-E-TENS + + ADD A,$0A ; reverse last subtraction + LD C,A ; transfer remainder to C + + LD A,B ; transfer ten value to A. + AND A ; test for zero. + JR Z,L16AD ; skip forward if so to PF-E-LOW + + CALL L07EB ; routine OUT-CODE prints as digit '1' - '9' + +;; PF-E-LOW +L16AD: LD A,C ; low byte to A + CALL L07EB ; routine OUT-CODE prints final digit of the + ; exponent. + RET ; return. >> + +; --- + +; this branch deals with zeros after decimal point. +; e.g. .01 or .0000999 + +;; PF-ZEROS +L16B2: NEG ; negate makes number positive 1 to 4. + LD B,A ; zero count to B. + + LD A,$1B ; prepare character '.' + RST 10H ; PRINT-A + + LD A,$1C ; prepare a '0' + +;; PF-ZRO-LP +L16BA: RST 10H ; PRINT-A + DJNZ L16BA ; loop back to PF-ZRO-LP + + JR L16C8 ; forward to PF-FRAC-LP + +; --- + +; there is a need to print a leading zero e.g. 0.1 but not with .01 + +;; PF-ZERO-1 +L16BF: LD A,$1C ; prepare character '0'. + RST 10H ; PRINT-A + +; this subroutine considers the decimal point and any trailing digits. +; if the next character is a marked zero, $80, then nothing more to print. + +;; PF-DC-OUT +L16C2: DEC (HL) ; decrement addressed character + INC (HL) ; increment it again + RET PE ; return with overflow (was 128) >> + ; as no fractional part + +; else there is a fractional part so print the decimal point. + + LD A,$1B ; prepare character '.' + RST 10H ; PRINT-A + +; now enter a loop to print trailing digits + +;; PF-FRAC-LP +L16C8: DEC (HL) ; test for a marked zero. + INC (HL) ; + RET PE ; return when digits exhausted >> + + CALL L16D0 ; routine PF-NIBBLE + JR L16C8 ; back for all fractional digits to PF-FRAC-LP. + +; --- + +; subroutine to print right-hand nibble + +;; PF-NIBBLE +L16D0: LD A,(HL) ; fetch addressed byte + AND $0F ; mask off lower 4 bits + CALL L07EB ; routine OUT-CODE + DEC HL ; decrement pointer. + RET ; return. + + +; ------------------------------- +; THE 'PREPARE TO ADD' SUBROUTINE +; ------------------------------- +; This routine is called twice to prepare each floating point number for +; addition, in situ, on the calculator stack. +; The exponent is picked up from the first byte which is then cleared to act +; as a sign byte and accept any overflow. +; If the exponent is zero then the number is zero and an early return is made. +; The now redundant sign bit of the mantissa is set and if the number is +; negative then all five bytes of the number are twos-complemented to prepare +; the number for addition. +; On the second invocation the exponent of the first number is in B. + + +;; PREP-ADD +L16D8: LD A,(HL) ; fetch exponent. + LD (HL),$00 ; make this byte zero to take any overflow and + ; default to positive. + AND A ; test stored exponent for zero. + RET Z ; return with zero flag set if number is zero. + + INC HL ; point to first byte of mantissa. + BIT 7,(HL) ; test the sign bit. + SET 7,(HL) ; set it to its implied state. + DEC HL ; set pointer to first byte again. + RET Z ; return if bit indicated number is positive.>> + +; if negative then all five bytes are twos complemented starting at LSB. + + PUSH BC ; save B register contents. + LD BC,$0005 ; set BC to five. + ADD HL,BC ; point to location after 5th byte. + LD B,C ; set the B counter to five. + LD C,A ; store original exponent in C. + SCF ; set carry flag so that one is added. + +; now enter a loop to twos-complement the number. +; The first of the five bytes becomes $FF to denote a negative number. + +;; NEG-BYTE +L16EC: DEC HL ; point to first or more significant byte. + LD A,(HL) ; fetch to accumulator. + CPL ; complement. + ADC A,$00 ; add in initial carry or any subsequent carry. + LD (HL),A ; place number back. + DJNZ L16EC ; loop back five times to NEG-BYTE + + LD A,C ; restore the exponent to accumulator. + POP BC ; restore B register contents. + + RET ; return. + +; ---------------------------------- +; THE 'FETCH TWO NUMBERS' SUBROUTINE +; ---------------------------------- +; This routine is used by addition, multiplication and division to fetch +; the two five-byte numbers addressed by HL and DE from the calculator stack +; into the Z80 registers. +; The HL register may no longer point to the first of the two numbers. +; Since the 32-bit addition operation is accomplished using two Z80 16-bit +; instructions, it is important that the lower two bytes of each mantissa are +; in one set of registers and the other bytes all in the alternate set. +; +; In: HL = highest number, DE= lowest number +; +; : alt': : +; Out: :H,B-C:C,B: num1 +; :L,D-E:D-E: num2 + +;; FETCH-TWO +L16F7: PUSH HL ; save HL + PUSH AF ; save A - result sign when used from division. + + LD C,(HL) ; + INC HL ; + LD B,(HL) ; + LD (HL),A ; insert sign when used from multiplication. + INC HL ; + LD A,C ; m1 + LD C,(HL) ; + PUSH BC ; PUSH m2 m3 + + INC HL ; + LD C,(HL) ; m4 + INC HL ; + LD B,(HL) ; m5 BC holds m5 m4 + + EX DE,HL ; make HL point to start of second number. + + LD D,A ; m1 + LD E,(HL) ; + PUSH DE ; PUSH m1 n1 + + INC HL ; + LD D,(HL) ; + INC HL ; + LD E,(HL) ; + PUSH DE ; PUSH n2 n3 + + EXX ; - - - - - - - + + POP DE ; POP n2 n3 + POP HL ; POP m1 n1 + POP BC ; POP m2 m3 + + EXX ; - - - - - - - + + INC HL ; + LD D,(HL) ; + INC HL ; + LD E,(HL) ; DE holds n4 n5 + + POP AF ; restore saved + POP HL ; registers. + RET ; return. + +; ----------------------------- +; THE 'SHIFT ADDEND' SUBROUTINE +; ----------------------------- +; The accumulator A contains the difference between the two exponents. +; This is the lowest of the two numbers to be added + +;; SHIFT-FP +L171A: AND A ; test difference between exponents. + RET Z ; return if zero. both normal. + + CP $21 ; compare with 33 bits. + JR NC,L1736 ; forward if greater than 32 to ADDEND-0 + + PUSH BC ; preserve BC - part + LD B,A ; shift counter to B. + +; Now perform B right shifts on the addend L'D'E'D E +; to bring it into line with the augend H'B'C'C B + +;; ONE-SHIFT +L1722: EXX ; - - - + SRA L ; 76543210->C bit 7 unchanged. + RR D ; C->76543210->C + RR E ; C->76543210->C + EXX ; - - - + RR D ; C->76543210->C + RR E ; C->76543210->C + DJNZ L1722 ; loop back B times to ONE-SHIFT + + POP BC ; restore BC + RET NC ; return if last shift produced no carry. >> + +; if carry flag was set then accuracy is being lost so round up the addend. + + CALL L1741 ; routine ADD-BACK + RET NZ ; return if not FF 00 00 00 00 + +; this branch makes all five bytes of the addend zero and is made during +; addition when the exponents are too far apart for the addend bits to +; affect the result. + +;; ADDEND-0 +L1736: EXX ; select alternate set for more significant + ; bytes. + XOR A ; clear accumulator. + + +; this entry point (from multiplication) sets four of the bytes to zero or if +; continuing from above, during addition, then all five bytes are set to zero. + +;; ZEROS-4/5 +L1738: LD L,$00 ; set byte 1 to zero. + LD D,A ; set byte 2 to A. + LD E,L ; set byte 3 to zero. + EXX ; select main set + LD DE,$0000 ; set lower bytes 4 and 5 to zero. + RET ; return. + +; ------------------------- +; THE 'ADD-BACK' SUBROUTINE +; ------------------------- +; Called from SHIFT-FP above during addition and after normalization from +; multiplication. +; This is really a 32-bit increment routine which sets the zero flag according +; to the 32-bit result. +; During addition, only negative numbers like FF FF FF FF FF, +; the twos-complement version of xx 80 00 00 01 say +; will result in a full ripple FF 00 00 00 00. +; FF FF FF FF FF when shifted right is unchanged by SHIFT-FP but sets the +; carry invoking this routine. + +;; ADD-BACK +L1741: INC E ; + RET NZ ; + + INC D ; + RET NZ ; + + EXX ; + INC E ; + JR NZ,L174A ; forward if no overflow to ALL-ADDED + + INC D ; + +;; ALL-ADDED +L174A: EXX ; + RET ; return with zero flag set for zero mantissa. + + +; --------------------------- +; THE 'SUBTRACTION' OPERATION +; --------------------------- +; just switch the sign of subtrahend and do an add. + +;; subtract +L174C: LD A,(DE) ; fetch exponent byte of second number the + ; subtrahend. + AND A ; test for zero + RET Z ; return if zero - first number is result. + + INC DE ; address the first mantissa byte. + LD A,(DE) ; fetch to accumulator. + XOR $80 ; toggle the sign bit. + LD (DE),A ; place back on calculator stack. + DEC DE ; point to exponent byte. + ; continue into addition routine. + +; ------------------------ +; THE 'ADDITION' OPERATION +; ------------------------ +; The addition operation pulls out all the stops and uses most of the Z80's +; registers to add two floating-point numbers. +; This is a binary operation and on entry, HL points to the first number +; and DE to the second. + +;; addition +L1755: EXX ; - - - + PUSH HL ; save the pointer to the next literal. + EXX ; - - - + + PUSH DE ; save pointer to second number + PUSH HL ; save pointer to first number - will be the + ; result pointer on calculator stack. + + CALL L16D8 ; routine PREP-ADD + LD B,A ; save first exponent byte in B. + EX DE,HL ; switch number pointers. + CALL L16D8 ; routine PREP-ADD + LD C,A ; save second exponent byte in C. + CP B ; compare the exponent bytes. + JR NC,L1769 ; forward if second higher to SHIFT-LEN + + LD A,B ; else higher exponent to A + LD B,C ; lower exponent to B + EX DE,HL ; switch the number pointers. + +;; SHIFT-LEN +L1769: PUSH AF ; save higher exponent + SUB B ; subtract lower exponent + + CALL L16F7 ; routine FETCH-TWO + CALL L171A ; routine SHIFT-FP + + POP AF ; restore higher exponent. + POP HL ; restore result pointer. + LD (HL),A ; insert exponent byte. + PUSH HL ; save result pointer again. + +; now perform the 32-bit addition using two 16-bit Z80 add instructions. + + LD L,B ; transfer low bytes of mantissa individually + LD H,C ; to HL register + + ADD HL,DE ; the actual binary addition of lower bytes + +; now the two higher byte pairs that are in the alternate register sets. + + EXX ; switch in set + EX DE,HL ; transfer high mantissa bytes to HL register. + + ADC HL,BC ; the actual addition of higher bytes with + ; any carry from first stage. + + EX DE,HL ; result in DE, sign bytes ($FF or $00) to HL + +; now consider the two sign bytes + + LD A,H ; fetch sign byte of num1 + + ADC A,L ; add including any carry from mantissa + ; addition. 00 or 01 or FE or FF + + LD L,A ; result in L. + +; possible outcomes of signs and overflow from mantissa are +; +; H + L + carry = L RRA XOR L RRA +; ------------------------------------------------------------ +; 00 + 00 = 00 00 00 +; 00 + 00 + carry = 01 00 01 carry +; FF + FF = FE C FF 01 carry +; FF + FF + carry = FF C FF 00 +; FF + 00 = FF FF 00 +; FF + 00 + carry = 00 C 80 80 + + RRA ; C->76543210->C + XOR L ; set bit 0 if shifting required. + + EXX ; switch back to main set + EX DE,HL ; full mantissa result now in D'E'D E registers. + POP HL ; restore pointer to result exponent on + ; the calculator stack. + + RRA ; has overflow occurred ? + JR NC,L1790 ; skip forward if not to TEST-NEG + +; if the addition of two positive mantissas produced overflow or if the +; addition of two negative mantissas did not then the result exponent has to +; be incremented and the mantissa shifted one place to the right. + + LD A,$01 ; one shift required. + CALL L171A ; routine SHIFT-FP performs a single shift + ; rounding any lost bit + INC (HL) ; increment the exponent. + JR Z,L17B3 ; forward to ADD-REP-6 if the exponent + ; wraps round from FF to zero as number is too + ; big for the system. + +; at this stage the exponent on the calculator stack is correct. + +;; TEST-NEG +L1790: EXX ; switch in the alternate set. + LD A,L ; load result sign to accumulator. + AND $80 ; isolate bit 7 from sign byte setting zero + ; flag if positive. + EXX ; back to main set. + + INC HL ; point to first byte of mantissa + LD (HL),A ; insert $00 positive or $80 negative at + ; position on calculator stack. + + DEC HL ; point to exponent again. + JR Z,L17B9 ; forward if positive to GO-NC-MLT + +; a negative number has to be twos-complemented before being placed on stack. + + LD A,E ; fetch lowest (rightmost) mantissa byte. + NEG ; Negate + CCF ; Complement Carry Flag + LD E,A ; place back in register + + LD A,D ; ditto + CPL ; + ADC A,$00 ; + LD D,A ; + + EXX ; switch to higher (leftmost) 16 bits. + + LD A,E ; ditto + CPL ; + ADC A,$00 ; + LD E,A ; + + LD A,D ; ditto + CPL ; + ADC A,$00 ; + JR NC,L17B7 ; forward without overflow to END-COMPL + +; else entire mantissa is now zero. 00 00 00 00 + + RRA ; set mantissa to 80 00 00 00 + EXX ; switch. + INC (HL) ; increment the exponent. + +;; ADD-REP-6 +L17B3: JP Z,L1880 ; jump forward if exponent now zero to REPORT-6 + ; 'Number too big' + + EXX ; switch back to alternate set. + +;; END-COMPL +L17B7: LD D,A ; put first byte of mantissa back in DE. + EXX ; switch to main set. + +;; GO-NC-MLT +L17B9: XOR A ; clear carry flag and + ; clear accumulator so no extra bits carried + ; forward as occurs in multiplication. + + JR L1828 ; forward to common code at TEST-NORM + ; but should go straight to NORMALIZE. + + +; ---------------------------------------------- +; THE 'PREPARE TO MULTIPLY OR DIVIDE' SUBROUTINE +; ---------------------------------------------- +; this routine is called twice from multiplication and twice from division +; to prepare each of the two numbers for the operation. +; Initially the accumulator holds zero and after the second invocation bit 7 +; of the accumulator will be the sign bit of the result. + +;; PREP-M/D +L17BC: SCF ; set carry flag to signal number is zero. + DEC (HL) ; test exponent + INC (HL) ; for zero. + RET Z ; return if zero with carry flag set. + + INC HL ; address first mantissa byte. + XOR (HL) ; exclusive or the running sign bit. + SET 7,(HL) ; set the implied bit. + DEC HL ; point to exponent byte. + RET ; return. + +; ------------------------------ +; THE 'MULTIPLICATION' OPERATION +; ------------------------------ +; +; + +;; multiply +L17C6: XOR A ; reset bit 7 of running sign flag. + CALL L17BC ; routine PREP-M/D + RET C ; return if number is zero. + ; zero * anything = zero. + + EXX ; - - - + PUSH HL ; save pointer to 'next literal' + EXX ; - - - + + PUSH DE ; save pointer to second number + + EX DE,HL ; make HL address second number. + + CALL L17BC ; routine PREP-M/D + + EX DE,HL ; HL first number, DE - second number + JR C,L1830 ; forward with carry to ZERO-RSLT + ; anything * zero = zero. + + PUSH HL ; save pointer to first number. + + CALL L16F7 ; routine FETCH-TWO fetches two mantissas from + ; calc stack to B'C'C,B D'E'D E + ; (HL will be overwritten but the result sign + ; in A is inserted on the calculator stack) + + LD A,B ; transfer low mantissa byte of first number + AND A ; clear carry. + SBC HL,HL ; a short form of LD HL,$0000 to take lower + ; two bytes of result. (2 program bytes) + EXX ; switch in alternate set + PUSH HL ; preserve HL + SBC HL,HL ; set HL to zero also to take higher two bytes + ; of the result and clear carry. + EXX ; switch back. + + LD B,$21 ; register B can now be used to count thirty + ; three shifts. + JR L17F8 ; forward to loop entry point STRT-MLT + +; --- + +; The multiplication loop is entered at STRT-LOOP. + +;; MLT-LOOP +L17E7: JR NC,L17EE ; forward if no carry to NO-ADD + + ; else add in the multiplicand. + + ADD HL,DE ; add the two low bytes to result + EXX ; switch to more significant bytes. + ADC HL,DE ; add high bytes of multiplicand and any carry. + EXX ; switch to main set. + +; in either case shift result right into B'C'C A + +;; NO-ADD +L17EE: EXX ; switch to alternate set + RR H ; C > 76543210 > C + RR L ; C > 76543210 > C + EXX ; + RR H ; C > 76543210 > C + RR L ; C > 76543210 > C + +;; STRT-MLT +L17F8: EXX ; switch in alternate set. + RR B ; C > 76543210 > C + RR C ; C > 76543210 > C + EXX ; now main set + RR C ; C > 76543210 > C + RRA ; C > 76543210 > C + DJNZ L17E7 ; loop back 33 times to MLT-LOOP + +; + + EX DE,HL ; + EXX ; + EX DE,HL ; + EXX ; + POP BC ; + POP HL ; + LD A,B ; + ADD A,C ; + JR NZ,L180E ; forward to MAKE-EXPT + + AND A ; + +;; MAKE-EXPT +L180E: DEC A ; + CCF ; Complement Carry Flag + +;; DIVN-EXPT +L1810: RLA ; + CCF ; Complement Carry Flag + RRA ; + JP P,L1819 ; forward to OFLW1-CLR + + JR NC,L1880 ; forward to REPORT-6 + + AND A ; + +;; OFLW1-CLR +L1819: INC A ; + JR NZ,L1824 ; forward to OFLW2-CLR + + JR C,L1824 ; forward to OFLW2-CLR + + EXX ; + BIT 7,D ; + EXX ; + JR NZ,L1880 ; forward to REPORT-6 + +;; OFLW2-CLR +L1824: LD (HL),A ; + EXX ; + LD A,B ; + EXX ; + +; addition joins here with carry flag clear. + +;; TEST-NORM +L1828: JR NC,L183F ; forward to NORMALIZE + + LD A,(HL) ; + AND A ; + +;; NEAR-ZERO +L182C: LD A,$80 ; prepare to rescue the most significant bit + ; of the mantissa if it is set. + JR Z,L1831 ; skip forward to SKIP-ZERO + +;; ZERO-RSLT +L1830: XOR A ; make mask byte zero signaling set five + ; bytes to zero. + +;; SKIP-ZERO +L1831: EXX ; switch in alternate set + AND D ; isolate most significant bit (if A is $80). + + CALL L1738 ; routine ZEROS-4/5 sets mantissa without + ; affecting any flags. + + RLCA ; test if MSB set. bit 7 goes to bit 0. + ; either $00 -> $00 or $80 -> $01 + LD (HL),A ; make exponent $01 (lowest) or $00 zero + JR C,L1868 ; forward if first case to OFLOW-CLR + + INC HL ; address first mantissa byte on the + ; calculator stack. + LD (HL),A ; insert a zero for the sign bit. + DEC HL ; point to zero exponent + JR L1868 ; forward to OFLOW-CLR + +; --- + +; this branch is common to addition and multiplication with the mantissa +; result still in registers D'E'D E . + +;; NORMALIZE +L183F: LD B,$20 ; a maximum of thirty-two left shifts will be + ; needed. + +;; SHIFT-ONE +L1841: EXX ; address higher 16 bits. + BIT 7,D ; test the leftmost bit + EXX ; address lower 16 bits. + + JR NZ,L1859 ; forward if leftmost bit was set to NORML-NOW + + RLCA ; this holds zero from addition, 33rd bit + ; from multiplication. + + RL E ; C < 76543210 < C + RL D ; C < 76543210 < C + + EXX ; address higher 16 bits. + + RL E ; C < 76543210 < C + RL D ; C < 76543210 < C + + EXX ; switch to main set. + + DEC (HL) ; decrement the exponent byte on the calculator + ; stack. + + JR Z,L182C ; back if exponent becomes zero to NEAR-ZERO + ; it's just possible that the last rotation + ; set bit 7 of D. We shall see. + + DJNZ L1841 ; loop back to SHIFT-ONE + +; if thirty-two left shifts were performed without setting the most significant +; bit then the result is zero. + + JR L1830 ; back to ZERO-RSLT + +; --- + +;; NORML-NOW +L1859: RLA ; for the addition path, A is always zero. + ; for the mult path, ... + + JR NC,L1868 ; forward to OFLOW-CLR + +; this branch is taken only with multiplication. + + CALL L1741 ; routine ADD-BACK + + JR NZ,L1868 ; forward to OFLOW-CLR + + EXX ; + LD D,$80 ; + EXX ; + INC (HL) ; + JR Z,L1880 ; forward to REPORT-6 + +; now transfer the mantissa from the register sets to the calculator stack +; incorporating the sign bit already there. + +;; OFLOW-CLR +L1868: PUSH HL ; save pointer to exponent on stack. + INC HL ; address first byte of mantissa which was + ; previously loaded with sign bit $00 or $80. + + EXX ; - - - + PUSH DE ; push the most significant two bytes. + EXX ; - - - + + POP BC ; pop - true mantissa is now BCDE. + +; now pick up the sign bit. + + LD A,B ; first mantissa byte to A + RLA ; rotate out bit 7 which is set + RL (HL) ; rotate sign bit on stack into carry. + RRA ; rotate sign bit into bit 7 of mantissa. + +; and transfer mantissa from main registers to calculator stack. + + LD (HL),A ; + INC HL ; + LD (HL),C ; + INC HL ; + LD (HL),D ; + INC HL ; + LD (HL),E ; + + POP HL ; restore pointer to num1 now result. + POP DE ; restore pointer to num2 now STKEND. + + EXX ; - - - + POP HL ; restore pointer to next calculator literal. + EXX ; - - - + + RET ; return. + +; --- + +;; REPORT-6 +L1880: RST 08H ; ERROR-1 + DEFB $05 ; Error Report: Arithmetic overflow. + +; ------------------------ +; THE 'DIVISION' OPERATION +; ------------------------ +; "Of all the arithmetic subroutines, division is the most complicated and +; the least understood. It is particularly interesting to note that the +; Sinclair programmer himself has made a mistake in his programming ( or has +; copied over someone else's mistake!) for +; PRINT PEEK 6352 [ $18D0 ] ('unimproved' ROM, 6351 [ $18CF ] ) +; should give 218 not 225." +; - Dr. Ian Logan, Syntax magazine Jul/Aug 1982. +; [ i.e. the jump should be made to div-34th ] + +; First check for division by zero. + +;; division +L1882: EX DE,HL ; consider the second number first. + XOR A ; set the running sign flag. + CALL L17BC ; routine PREP-M/D + JR C,L1880 ; back if zero to REPORT-6 + ; 'Arithmetic overflow' + + EX DE,HL ; now prepare first number and check for zero. + CALL L17BC ; routine PREP-M/D + RET C ; return if zero, 0/anything is zero. + + EXX ; - - - + PUSH HL ; save pointer to the next calculator literal. + EXX ; - - - + + PUSH DE ; save pointer to divisor - will be STKEND. + PUSH HL ; save pointer to dividend - will be result. + + CALL L16F7 ; routine FETCH-TWO fetches the two numbers + ; into the registers H'B'C'C B + ; L'D'E'D E + EXX ; - - - + PUSH HL ; save the two exponents. + + LD H,B ; transfer the dividend to H'L'H L + LD L,C ; + EXX ; + LD H,C ; + LD L,B ; + + XOR A ; clear carry bit and accumulator. + LD B,$DF ; count upwards from -33 decimal + JR L18B2 ; forward to mid-loop entry point DIV-START + +; --- + +;; DIV-LOOP +L18A2: RLA ; multiply partial quotient by two + RL C ; setting result bit from carry. + EXX ; + RL C ; + RL B ; + EXX ; + +;; div-34th +L18AB: ADD HL,HL ; + EXX ; + ADC HL,HL ; + EXX ; + JR C,L18C2 ; forward to SUBN-ONLY + +;; DIV-START +L18B2: SBC HL,DE ; subtract divisor part. + EXX ; + SBC HL,DE ; + EXX ; + JR NC,L18C9 ; forward if subtraction goes to NO-RSTORE + + ADD HL,DE ; else restore + EXX ; + ADC HL,DE ; + EXX ; + AND A ; clear carry + JR L18CA ; forward to COUNT-ONE + +; --- + +;; SUBN-ONLY +L18C2: AND A ; + SBC HL,DE ; + EXX ; + SBC HL,DE ; + EXX ; + +;; NO-RSTORE +L18C9: SCF ; set carry flag + +;; COUNT-ONE +L18CA: INC B ; increment the counter + JP M,L18A2 ; back while still minus to DIV-LOOP + + PUSH AF ; + JR Z,L18B2 ; back to DIV-START + +; "This jump is made to the wrong place. No 34th bit will ever be obtained +; without first shifting the dividend. Hence important results like 1/10 and +; 1/1000 are not rounded up as they should be. Rounding up never occurs when +; it depends on the 34th bit. The jump should be made to div-34th above." +; - Dr. Frank O'Hara, "The Complete Spectrum ROM Disassembly", 1983, +; published by Melbourne House. +; (Note. on the ZX81 this would be JR Z,L18AB) +; +; However if you make this change, then while (1/2=.5) will now evaluate as +; true, (.25=1/4), which did evaluate as true, no longer does. + + LD E,A ; + LD D,C ; + EXX ; + LD E,C ; + LD D,B ; + + POP AF ; + RR B ; + POP AF ; + RR B ; + + EXX ; + POP BC ; + POP HL ; + LD A,B ; + SUB C ; + JP L1810 ; jump back to DIVN-EXPT + +; ------------------------------------------------ +; THE 'INTEGER TRUNCATION TOWARDS ZERO' SUBROUTINE +; ------------------------------------------------ +; + +;; truncate +L18E4: LD A,(HL) ; fetch exponent + CP $81 ; compare to +1 + JR NC,L18EF ; forward, if 1 or more, to T-GR-ZERO + +; else the number is smaller than plus or minus 1 and can be made zero. + + LD (HL),$00 ; make exponent zero. + LD A,$20 ; prepare to set 32 bits of mantissa to zero. + JR L18F4 ; forward to NIL-BYTES + +; --- + +;; T-GR-ZERO +L18EF: SUB $A0 ; subtract +32 from exponent + RET P ; return if result is positive as all 32 bits + ; of the mantissa relate to the integer part. + ; The floating point is somewhere to the right + ; of the mantissa + + NEG ; else negate to form number of rightmost bits + ; to be blanked. + +; for instance, disregarding the sign bit, the number 3.5 is held as +; exponent $82 mantissa .11100000 00000000 00000000 00000000 +; we need to set $82 - $A0 = $E2 NEG = $1E (thirty) bits to zero to form the +; integer. +; The sign of the number is never considered as the first bit of the mantissa +; must be part of the integer. + +;; NIL-BYTES +L18F4: PUSH DE ; save pointer to STKEND + EX DE,HL ; HL points at STKEND + DEC HL ; now at last byte of mantissa. + LD B,A ; Transfer bit count to B register. + SRL B ; divide by + SRL B ; eight + SRL B ; + JR Z,L1905 ; forward if zero to BITS-ZERO + +; else the original count was eight or more and whole bytes can be blanked. + +;; BYTE-ZERO +L1900: LD (HL),$00 ; set eight bits to zero. + DEC HL ; point to more significant byte of mantissa. + DJNZ L1900 ; loop back to BYTE-ZERO + +; now consider any residual bits. + +;; BITS-ZERO +L1905: AND $07 ; isolate the remaining bits + JR Z,L1912 ; forward if none to IX-END + + LD B,A ; transfer bit count to B counter. + LD A,$FF ; form a mask 11111111 + +;; LESS-MASK +L190C: SLA A ; 1 <- 76543210 <- o slide mask leftwards. + DJNZ L190C ; loop back for bit count to LESS-MASK + + AND (HL) ; lose the unwanted rightmost bits + LD (HL),A ; and place in mantissa byte. + +;; IX-END +L1912: EX DE,HL ; restore result pointer from DE. + POP DE ; restore STKEND from stack. + RET ; return. + + +;******************************** +;** FLOATING-POINT CALCULATOR ** +;******************************** + +; As a general rule the calculator avoids using the IY register. +; Exceptions are val and str$. +; So an assembly language programmer who has disabled interrupts to use IY +; for other purposes can still use the calculator for mathematical +; purposes. + + +; ------------------------ +; THE 'TABLE OF CONSTANTS' +; ------------------------ +; The ZX81 has only floating-point number representation. +; Both the ZX80 and the ZX Spectrum have integer numbers in some form. + +;; stk-zero 00 00 00 00 00 +L1915: DEFB $00 ;;Bytes: 1 + DEFB $B0 ;;Exponent $00 + DEFB $00 ;;(+00,+00,+00) + +;; stk-one 81 00 00 00 00 +L1918: DEFB $31 ;;Exponent $81, Bytes: 1 + DEFB $00 ;;(+00,+00,+00) + + +;; stk-half 80 00 00 00 00 +L191A: DEFB $30 ;;Exponent: $80, Bytes: 1 + DEFB $00 ;;(+00,+00,+00) + + +;; stk-pi/2 81 49 0F DA A2 +L191C: DEFB $F1 ;;Exponent: $81, Bytes: 4 + DEFB $49,$0F,$DA,$A2 ;; + +;; stk-ten 84 20 00 00 00 +L1921: DEFB $34 ;;Exponent: $84, Bytes: 1 + DEFB $20 ;;(+00,+00,+00) + + +; ------------------------ +; THE 'TABLE OF ADDRESSES' +; ------------------------ +; +; starts with binary operations which have two operands and one result. +; three pseudo binary operations first. + +;; tbl-addrs +L1923: DEFW L1C2F ; $00 Address: $1C2F - jump-true + DEFW L1A72 ; $01 Address: $1A72 - exchange + DEFW L19E3 ; $02 Address: $19E3 - delete + +; true binary operations. + + DEFW L174C ; $03 Address: $174C - subtract + DEFW L17C6 ; $04 Address: $176C - multiply + DEFW L1882 ; $05 Address: $1882 - division + DEFW L1DE2 ; $06 Address: $1DE2 - to-power + DEFW L1AED ; $07 Address: $1AED - or + + DEFW L1AF3 ; $08 Address: $1B03 - no-&-no + DEFW L1B03 ; $09 Address: $1B03 - no-l-eql + DEFW L1B03 ; $0A Address: $1B03 - no-gr-eql + DEFW L1B03 ; $0B Address: $1B03 - nos-neql + DEFW L1B03 ; $0C Address: $1B03 - no-grtr + DEFW L1B03 ; $0D Address: $1B03 - no-less + DEFW L1B03 ; $0E Address: $1B03 - nos-eql + DEFW L1755 ; $0F Address: $1755 - addition + + DEFW L1AF8 ; $10 Address: $1AF8 - str-&-no + DEFW L1B03 ; $11 Address: $1B03 - str-l-eql + DEFW L1B03 ; $12 Address: $1B03 - str-gr-eql + DEFW L1B03 ; $13 Address: $1B03 - strs-neql + DEFW L1B03 ; $14 Address: $1B03 - str-grtr + DEFW L1B03 ; $15 Address: $1B03 - str-less + DEFW L1B03 ; $16 Address: $1B03 - strs-eql + DEFW L1B62 ; $17 Address: $1B62 - strs-add + +; unary follow + + DEFW L1AA0 ; $18 Address: $1AA0 - neg + + DEFW L1C06 ; $19 Address: $1C06 - code + DEFW L1BA4 ; $1A Address: $1BA4 - val + DEFW L1C11 ; $1B Address: $1C11 - len + DEFW L1D49 ; $1C Address: $1D49 - sin + DEFW L1D3E ; $1D Address: $1D3E - cos + DEFW L1D6E ; $1E Address: $1D6E - tan + DEFW L1DC4 ; $1F Address: $1DC4 - asn + DEFW L1DD4 ; $20 Address: $1DD4 - acs + DEFW L1D76 ; $21 Address: $1D76 - atn + DEFW L1CA9 ; $22 Address: $1CA9 - ln + DEFW L1C5B ; $23 Address: $1C5B - exp + DEFW L1C46 ; $24 Address: $1C46 - int + DEFW L1DDB ; $25 Address: $1DDB - sqr + DEFW L1AAF ; $26 Address: $1AAF - sgn + DEFW L1AAA ; $27 Address: $1AAA - abs + DEFW L1ABE ; $28 Address: $1A1B - peek + DEFW L1AC5 ; $29 Address: $1AC5 - usr-no + DEFW L1BD5 ; $2A Address: $1BD5 - str$ + DEFW L1B8F ; $2B Address: $1B8F - chrs + DEFW L1AD5 ; $2C Address: $1AD5 - not + +; end of true unary + + DEFW L19F6 ; $2D Address: $19F6 - duplicate + DEFW L1C37 ; $2E Address: $1C37 - n-mod-m + + DEFW L1C23 ; $2F Address: $1C23 - jump + DEFW L19FC ; $30 Address: $19FC - stk-data + + DEFW L1C17 ; $31 Address: $1C17 - dec-jr-nz + DEFW L1ADB ; $32 Address: $1ADB - less-0 + DEFW L1ACE ; $33 Address: $1ACE - greater-0 + DEFW L002B ; $34 Address: $002B - end-calc + DEFW L1D18 ; $35 Address: $1D18 - get-argt + DEFW L18E4 ; $36 Address: $18E4 - truncate + DEFW L19E4 ; $37 Address: $19E4 - fp-calc-2 + DEFW L155A ; $38 Address: $155A - e-to-fp + +; the following are just the next available slots for the 128 compound literals +; which are in range $80 - $FF. + + DEFW L1A7F ; $39 Address: $1A7F - series-xx $80 - $9F. + DEFW L1A51 ; $3A Address: $1A51 - stk-const-xx $A0 - $BF. + DEFW L1A63 ; $3B Address: $1A63 - st-mem-xx $C0 - $DF. + DEFW L1A45 ; $3C Address: $1A45 - get-mem-xx $E0 - $FF. + +; Aside: 3D - 7F are therefore unused calculator literals. +; 39 - 7B would be available for expansion. + +; ------------------------------- +; THE 'FLOATING POINT CALCULATOR' +; ------------------------------- +; +; + +;; CALCULATE +L199D: CALL L1B85 ; routine STK-PNTRS is called to set up the + ; calculator stack pointers for a default + ; unary operation. HL = last value on stack. + ; DE = STKEND first location after stack. + +; the calculate routine is called at this point by the series generator... + +;; GEN-ENT-1 +L19A0: LD A,B ; fetch the Z80 B register to A + LD ($401E),A ; and store value in system variable BREG. + ; this will be the counter for dec-jr-nz + ; or if used from fp-calc2 the calculator + ; instruction. + +; ... and again later at this point + +;; GEN-ENT-2 +L19A4: EXX ; switch sets + EX (SP),HL ; and store the address of next instruction, + ; the return address, in H'L'. + ; If this is a recursive call then the H'L' + ; of the previous invocation goes on stack. + ; c.f. end-calc. + EXX ; switch back to main set. + +; this is the re-entry looping point when handling a string of literals. + +;; RE-ENTRY +L19A7: LD ($401C),DE ; save end of stack in system variable STKEND + EXX ; switch to alt + LD A,(HL) ; get next literal + INC HL ; increase pointer' + +; single operation jumps back to here + +;; SCAN-ENT +L19AE: PUSH HL ; save pointer on stack * + AND A ; now test the literal + JP P,L19C2 ; forward to FIRST-3D if in range $00 - $3D + ; anything with bit 7 set will be one of + ; 128 compound literals. + +; compound literals have the following format. +; bit 7 set indicates compound. +; bits 6-5 the subgroup 0-3. +; bits 4-0 the embedded parameter $00 - $1F. +; The subgroup 0-3 needs to be manipulated to form the next available four +; address places after the simple literals in the address table. + + LD D,A ; save literal in D + AND $60 ; and with 01100000 to isolate subgroup + RRCA ; rotate bits + RRCA ; 4 places to right + RRCA ; not five as we need offset * 2 + RRCA ; 00000xx0 + ADD A,$72 ; add ($39 * 2) to give correct offset. + ; alter above if you add more literals. + LD L,A ; store in L for later indexing. + LD A,D ; bring back compound literal + AND $1F ; use mask to isolate parameter bits + JR L19D0 ; forward to ENT-TABLE + +; --- + +; the branch was here with simple literals. + +;; FIRST-3D +L19C2: CP $18 ; compare with first unary operations. + JR NC,L19CE ; to DOUBLE-A with unary operations + +; it is binary so adjust pointers. + + EXX ; + LD BC,$FFFB ; the value -5 + LD D,H ; transfer HL, the last value, to DE. + LD E,L ; + ADD HL,BC ; subtract 5 making HL point to second + ; value. + EXX ; + +;; DOUBLE-A +L19CE: RLCA ; double the literal + LD L,A ; and store in L for indexing + +;; ENT-TABLE +L19D0: LD DE,L1923 ; Address: tbl-addrs + LD H,$00 ; prepare to index + ADD HL,DE ; add to get address of routine + LD E,(HL) ; low byte to E + INC HL ; + LD D,(HL) ; high byte to D + + LD HL,L19A7 ; Address: RE-ENTRY + EX (SP),HL ; goes on machine stack + ; address of next literal goes to HL. * + + + PUSH DE ; now the address of routine is stacked. + EXX ; back to main set + ; avoid using IY register. + LD BC,($401D) ; STKEND_hi + ; nothing much goes to C but BREG to B + ; and continue into next ret instruction + ; which has a dual identity + + +; ----------------------- +; THE 'DELETE' SUBROUTINE +; ----------------------- +; offset $02: 'delete' +; A simple return but when used as a calculator literal this +; deletes the last value from the calculator stack. +; On entry, as always with binary operations, +; HL=first number, DE=second number +; On exit, HL=result, DE=stkend. +; So nothing to do + +;; delete +L19E3: RET ; return - indirect jump if from above. + +; --------------------------------- +; THE 'SINGLE OPERATION' SUBROUTINE +; --------------------------------- +; offset $37: 'fp-calc-2' +; this single operation is used, in the first instance, to evaluate most +; of the mathematical and string functions found in BASIC expressions. + +;; fp-calc-2 +L19E4: POP AF ; drop return address. + LD A,($401E) ; load accumulator from system variable BREG + ; value will be literal eg. 'tan' + EXX ; switch to alt + JR L19AE ; back to SCAN-ENT + ; next literal will be end-calc in scanning + +; ------------------------------ +; THE 'TEST 5 SPACES' SUBROUTINE +; ------------------------------ +; This routine is called from MOVE-FP, STK-CONST and STK-STORE to +; test that there is enough space between the calculator stack and the +; machine stack for another five-byte value. It returns with BC holding +; the value 5 ready for any subsequent LDIR. + +;; TEST-5-SP +L19EB: PUSH DE ; save + PUSH HL ; registers + LD BC,$0005 ; an overhead of five bytes + CALL L0EC5 ; routine TEST-ROOM tests free RAM raising + ; an error if not. + POP HL ; else restore + POP DE ; registers. + RET ; return with BC set at 5. + + +; --------------------------------------------- +; THE 'MOVE A FLOATING POINT NUMBER' SUBROUTINE +; --------------------------------------------- +; offset $2D: 'duplicate' +; This simple routine is a 5-byte LDIR instruction +; that incorporates a memory check. +; When used as a calculator literal it duplicates the last value on the +; calculator stack. +; Unary so on entry HL points to last value, DE to stkend + +;; duplicate +;; MOVE-FP +L19F6: CALL L19EB ; routine TEST-5-SP test free memory + ; and sets BC to 5. + LDIR ; copy the five bytes. + RET ; return with DE addressing new STKEND + ; and HL addressing new last value. + +; ------------------------------- +; THE 'STACK LITERALS' SUBROUTINE +; ------------------------------- +; offset $30: 'stk-data' +; When a calculator subroutine needs to put a value on the calculator +; stack that is not a regular constant this routine is called with a +; variable number of following data bytes that convey to the routine +; the floating point form as succinctly as is possible. + +;; stk-data +L19FC: LD H,D ; transfer STKEND + LD L,E ; to HL for result. + +;; STK-CONST +L19FE: CALL L19EB ; routine TEST-5-SP tests that room exists + ; and sets BC to $05. + + EXX ; switch to alternate set + PUSH HL ; save the pointer to next literal on stack + EXX ; switch back to main set + + EX (SP),HL ; pointer to HL, destination to stack. + + PUSH BC ; save BC - value 5 from test room ??. + + LD A,(HL) ; fetch the byte following 'stk-data' + AND $C0 ; isolate bits 7 and 6 + RLCA ; rotate + RLCA ; to bits 1 and 0 range $00 - $03. + LD C,A ; transfer to C + INC C ; and increment to give number of bytes + ; to read. $01 - $04 + LD A,(HL) ; reload the first byte + AND $3F ; mask off to give possible exponent. + JR NZ,L1A14 ; forward to FORM-EXP if it was possible to + ; include the exponent. + +; else byte is just a byte count and exponent comes next. + + INC HL ; address next byte and + LD A,(HL) ; pick up the exponent ( - $50). + +;; FORM-EXP +L1A14: ADD A,$50 ; now add $50 to form actual exponent + LD (DE),A ; and load into first destination byte. + LD A,$05 ; load accumulator with $05 and + SUB C ; subtract C to give count of trailing + ; zeros plus one. + INC HL ; increment source + INC DE ; increment destination + LD B,$00 ; prepare to copy + LDIR ; copy C bytes + + POP BC ; restore 5 counter to BC ??. + + EX (SP),HL ; put HL on stack as next literal pointer + ; and the stack value - result pointer - + ; to HL. + + EXX ; switch to alternate set. + POP HL ; restore next literal pointer from stack + ; to H'L'. + EXX ; switch back to main set. + + LD B,A ; zero count to B + XOR A ; clear accumulator + +;; STK-ZEROS +L1A27: DEC B ; decrement B counter + RET Z ; return if zero. >> + ; DE points to new STKEND + ; HL to new number. + + LD (DE),A ; else load zero to destination + INC DE ; increase destination + JR L1A27 ; loop back to STK-ZEROS until done. + +; ------------------------------- +; THE 'SKIP CONSTANTS' SUBROUTINE +; ------------------------------- +; This routine traverses variable-length entries in the table of constants, +; stacking intermediate, unwanted constants onto a dummy calculator stack, +; in the first five bytes of the ZX81 ROM. + +;; SKIP-CONS +L1A2D: AND A ; test if initially zero. + +;; SKIP-NEXT +L1A2E: RET Z ; return if zero. >> + + PUSH AF ; save count. + PUSH DE ; and normal STKEND + + LD DE,$0000 ; dummy value for STKEND at start of ROM + ; Note. not a fault but this has to be + ; moved elsewhere when running in RAM. + ; + CALL L19FE ; routine STK-CONST works through variable + ; length records. + + POP DE ; restore real STKEND + POP AF ; restore count + DEC A ; decrease + JR L1A2E ; loop back to SKIP-NEXT + +; -------------------------------- +; THE 'MEMORY LOCATION' SUBROUTINE +; -------------------------------- +; This routine, when supplied with a base address in HL and an index in A, +; will calculate the address of the A'th entry, where each entry occupies +; five bytes. It is used for addressing floating-point numbers in the +; calculator's memory area. + +;; LOC-MEM +L1A3C: LD C,A ; store the original number $00-$1F. + RLCA ; double. + RLCA ; quadruple. + ADD A,C ; now add original value to multiply by five. + + LD C,A ; place the result in C. + LD B,$00 ; set B to 0. + ADD HL,BC ; add to form address of start of number in HL. + + RET ; return. + +; ------------------------------------- +; THE 'GET FROM MEMORY AREA' SUBROUTINE +; ------------------------------------- +; offsets $E0 to $FF: 'get-mem-0', 'get-mem-1' etc. +; A holds $00-$1F offset. +; The calculator stack increases by 5 bytes. + +;; get-mem-xx +L1A45: PUSH DE ; save STKEND + LD HL,($401F) ; MEM is base address of the memory cells. + CALL L1A3C ; routine LOC-MEM so that HL = first byte + CALL L19F6 ; routine MOVE-FP moves 5 bytes with memory + ; check. + ; DE now points to new STKEND. + POP HL ; the original STKEND is now RESULT pointer. + RET ; return. + +; --------------------------------- +; THE 'STACK A CONSTANT' SUBROUTINE +; --------------------------------- +; offset $A0: 'stk-zero' +; offset $A1: 'stk-one' +; offset $A2: 'stk-half' +; offset $A3: 'stk-pi/2' +; offset $A4: 'stk-ten' +; This routine allows a one-byte instruction to stack up to 32 constants +; held in short form in a table of constants. In fact only 5 constants are +; required. On entry the A register holds the literal ANDed with $1F. +; It isn't very efficient and it would have been better to hold the +; numbers in full, five byte form and stack them in a similar manner +; to that which would be used later for semi-tone table values. + +;; stk-const-xx +L1A51: LD H,D ; save STKEND - required for result + LD L,E ; + EXX ; swap + PUSH HL ; save pointer to next literal + LD HL,L1915 ; Address: stk-zero - start of table of + ; constants + EXX ; + CALL L1A2D ; routine SKIP-CONS + CALL L19FE ; routine STK-CONST + EXX ; + POP HL ; restore pointer to next literal. + EXX ; + RET ; return. + +; --------------------------------------- +; THE 'STORE IN A MEMORY AREA' SUBROUTINE +; --------------------------------------- +; Offsets $C0 to $DF: 'st-mem-0', 'st-mem-1' etc. +; Although 32 memory storage locations can be addressed, only six +; $C0 to $C5 are required by the ROM and only the thirty bytes (6*5) +; required for these are allocated. ZX81 programmers who wish to +; use the floating point routines from assembly language may wish to +; alter the system variable MEM to point to 160 bytes of RAM to have +; use the full range available. +; A holds derived offset $00-$1F. +; Unary so on entry HL points to last value, DE to STKEND. + +;; st-mem-xx +L1A63: PUSH HL ; save the result pointer. + EX DE,HL ; transfer to DE. + LD HL,($401F) ; fetch MEM the base of memory area. + CALL L1A3C ; routine LOC-MEM sets HL to the destination. + EX DE,HL ; swap - HL is start, DE is destination. + CALL L19F6 ; routine MOVE-FP. + ; note. a short ld bc,5; ldir + ; the embedded memory check is not required + ; so these instructions would be faster! + EX DE,HL ; DE = STKEND + POP HL ; restore original result pointer + RET ; return. + +; ------------------------- +; THE 'EXCHANGE' SUBROUTINE +; ------------------------- +; offset $01: 'exchange' +; This routine exchanges the last two values on the calculator stack +; On entry, as always with binary operations, +; HL=first number, DE=second number +; On exit, HL=result, DE=stkend. + +;; exchange +L1A72: LD B,$05 ; there are five bytes to be swapped + +; start of loop. + +;; SWAP-BYTE +L1A74: LD A,(DE) ; each byte of second + LD C,(HL) ; each byte of first + EX DE,HL ; swap pointers + LD (DE),A ; store each byte of first + LD (HL),C ; store each byte of second + INC HL ; advance both + INC DE ; pointers. + DJNZ L1A74 ; loop back to SWAP-BYTE until all 5 done. + + EX DE,HL ; even up the exchanges + ; so that DE addresses STKEND. + RET ; return. + +; --------------------------------- +; THE 'SERIES GENERATOR' SUBROUTINE +; --------------------------------- +; offset $86: 'series-06' +; offset $88: 'series-08' +; offset $8C: 'series-0C' +; The ZX81 uses Chebyshev polynomials to generate approximations for +; SIN, ATN, LN and EXP. These are named after the Russian mathematician +; Pafnuty Chebyshev, born in 1821, who did much pioneering work on numerical +; series. As far as calculators are concerned, Chebyshev polynomials have an +; advantage over other series, for example the Taylor series, as they can +; reach an approximation in just six iterations for SIN, eight for EXP and +; twelve for LN and ATN. The mechanics of the routine are interesting but +; for full treatment of how these are generated with demonstrations in +; Sinclair BASIC see "The Complete Spectrum ROM Disassembly" by Dr Ian Logan +; and Dr Frank O'Hara, published 1983 by Melbourne House. + +;; series-xx +L1A7F: LD B,A ; parameter $00 - $1F to B counter + CALL L19A0 ; routine GEN-ENT-1 is called. + ; A recursive call to a special entry point + ; in the calculator that puts the B register + ; in the system variable BREG. The return + ; address is the next location and where + ; the calculator will expect its first + ; instruction - now pointed to by HL'. + ; The previous pointer to the series of + ; five-byte numbers goes on the machine stack. + +; The initialization phase. + + DEFB $2D ;;duplicate x,x + DEFB $0F ;;addition x+x + DEFB $C0 ;;st-mem-0 x+x + DEFB $02 ;;delete . + DEFB $A0 ;;stk-zero 0 + DEFB $C2 ;;st-mem-2 0 + +; a loop is now entered to perform the algebraic calculation for each of +; the numbers in the series + +;; G-LOOP +L1A89: DEFB $2D ;;duplicate v,v. + DEFB $E0 ;;get-mem-0 v,v,x+2 + DEFB $04 ;;multiply v,v*x+2 + DEFB $E2 ;;get-mem-2 v,v*x+2,v + DEFB $C1 ;;st-mem-1 + DEFB $03 ;;subtract + DEFB $34 ;;end-calc + +; the previous pointer is fetched from the machine stack to H'L' where it +; addresses one of the numbers of the series following the series literal. + + CALL L19FC ; routine STK-DATA is called directly to + ; push a value and advance H'L'. + CALL L19A4 ; routine GEN-ENT-2 recursively re-enters + ; the calculator without disturbing + ; system variable BREG + ; H'L' value goes on the machine stack and is + ; then loaded as usual with the next address. + + DEFB $0F ;;addition + DEFB $01 ;;exchange + DEFB $C2 ;;st-mem-2 + DEFB $02 ;;delete + + DEFB $31 ;;dec-jr-nz + DEFB $EE ;;back to L1A89, G-LOOP + +; when the counted loop is complete the final subtraction yields the result +; for example SIN X. + + DEFB $E1 ;;get-mem-1 + DEFB $03 ;;subtract + DEFB $34 ;;end-calc + + RET ; return with H'L' pointing to location + ; after last number in series. + +; ----------------------- +; Handle unary minus (18) +; ----------------------- +; Unary so on entry HL points to last value, DE to STKEND. + +;; NEGATE +;; negate +L1AA0: LD A, (HL) ; fetch exponent of last value on the + ; calculator stack. + AND A ; test it. + RET Z ; return if zero. + + INC HL ; address the byte with the sign bit. + LD A,(HL) ; fetch to accumulator. + XOR $80 ; toggle the sign bit. + LD (HL),A ; put it back. + DEC HL ; point to last value again. + RET ; return. + +; ----------------------- +; Absolute magnitude (27) +; ----------------------- +; This calculator literal finds the absolute value of the last value, +; floating point, on calculator stack. + +;; abs +L1AAA: INC HL ; point to byte with sign bit. + RES 7,(HL) ; make the sign positive. + DEC HL ; point to last value again. + RET ; return. + +; ----------- +; Signum (26) +; ----------- +; This routine replaces the last value on the calculator stack, +; which is in floating point form, with one if positive and with -minus one +; if negative. If it is zero then it is left as such. + +;; sgn +L1AAF: INC HL ; point to first byte of 4-byte mantissa. + LD A,(HL) ; pick up the byte with the sign bit. + DEC HL ; point to exponent. + DEC (HL) ; test the exponent for + INC (HL) ; the value zero. + + SCF ; set the carry flag. + CALL NZ,L1AE0 ; routine FP-0/1 replaces last value with one + ; if exponent indicates the value is non-zero. + ; in either case mantissa is now four zeros. + + INC HL ; point to first byte of 4-byte mantissa. + RLCA ; rotate original sign bit to carry. + RR (HL) ; rotate the carry into sign. + DEC HL ; point to last value. + RET ; return. + + +; ------------------------- +; Handle PEEK function (28) +; ------------------------- +; This function returns the contents of a memory address. +; The entire address space can be peeked including the ROM. + +;; peek +L1ABE: CALL L0EA7 ; routine FIND-INT puts address in BC. + LD A,(BC) ; load contents into A register. + +;; IN-PK-STK +L1AC2: JP L151D ; exit via STACK-A to put value on the + ; calculator stack. + +; --------------- +; USR number (29) +; --------------- +; The USR function followed by a number 0-65535 is the method by which +; the ZX81 invokes machine code programs. This function returns the +; contents of the BC register pair. +; Note. that STACK-BC re-initializes the IY register to $4000 if a user-written +; program has altered it. + +;; usr-no +L1AC5: CALL L0EA7 ; routine FIND-INT to fetch the + ; supplied address into BC. + + LD HL,L1520 ; address: STACK-BC is + PUSH HL ; pushed onto the machine stack. + PUSH BC ; then the address of the machine code + ; routine. + + RET ; make an indirect jump to the routine + ; and, hopefully, to STACK-BC also. + + +; ----------------------- +; Greater than zero ($33) +; ----------------------- +; Test if the last value on the calculator stack is greater than zero. +; This routine is also called directly from the end-tests of the comparison +; routine. + +;; GREATER-0 +;; greater-0 +L1ACE: LD A,(HL) ; fetch exponent. + AND A ; test it for zero. + RET Z ; return if so. + + + LD A,$FF ; prepare XOR mask for sign bit + JR L1ADC ; forward to SIGN-TO-C + ; to put sign in carry + ; (carry will become set if sign is positive) + ; and then overwrite location with 1 or 0 + ; as appropriate. + +; ------------------------ +; Handle NOT operator ($2C) +; ------------------------ +; This overwrites the last value with 1 if it was zero else with zero +; if it was any other value. +; +; e.g. NOT 0 returns 1, NOT 1 returns 0, NOT -3 returns 0. +; +; The subroutine is also called directly from the end-tests of the comparison +; operator. + +;; NOT +;; not +L1AD5: LD A,(HL) ; get exponent byte. + NEG ; negate - sets carry if non-zero. + CCF ; complement so carry set if zero, else reset. + JR L1AE0 ; forward to FP-0/1. + +; ------------------- +; Less than zero (32) +; ------------------- +; Destructively test if last value on calculator stack is less than zero. +; Bit 7 of second byte will be set if so. + +;; less-0 +L1ADB: XOR A ; set xor mask to zero + ; (carry will become set if sign is negative). + +; transfer sign of mantissa to Carry Flag. + +;; SIGN-TO-C +L1ADC: INC HL ; address 2nd byte. + XOR (HL) ; bit 7 of HL will be set if number is negative. + DEC HL ; address 1st byte again. + RLCA ; rotate bit 7 of A to carry. + +; ----------- +; Zero or one +; ----------- +; This routine places an integer value zero or one at the addressed location +; of calculator stack or MEM area. The value one is written if carry is set on +; entry else zero. + +;; FP-0/1 +L1AE0: PUSH HL ; save pointer to the first byte + LD B,$05 ; five bytes to do. + +;; FP-loop +L1AE3: LD (HL),$00 ; insert a zero. + INC HL ; + DJNZ L1AE3 ; repeat. + + POP HL ; + RET NC ; + + LD (HL),$81 ; make value 1 + RET ; return. + + +; ----------------------- +; Handle OR operator (07) +; ----------------------- +; The Boolean OR operator. eg. X OR Y +; The result is zero if both values are zero else a non-zero value. +; +; e.g. 0 OR 0 returns 0. +; -3 OR 0 returns -3. +; 0 OR -3 returns 1. +; -3 OR 2 returns 1. +; +; A binary operation. +; On entry HL points to first operand (X) and DE to second operand (Y). + +;; or +L1AED: LD A,(DE) ; fetch exponent of second number + AND A ; test it. + RET Z ; return if zero. + + SCF ; set carry flag + JR L1AE0 ; back to FP-0/1 to overwrite the first operand + ; with the value 1. + + +; ----------------------------- +; Handle number AND number (08) +; ----------------------------- +; The Boolean AND operator. +; +; e.g. -3 AND 2 returns -3. +; -3 AND 0 returns 0. +; 0 and -2 returns 0. +; 0 and 0 returns 0. +; +; Compare with OR routine above. + +;; no-&-no +L1AF3: LD A,(DE) ; fetch exponent of second number. + AND A ; test it. + RET NZ ; return if not zero. + + JR L1AE0 ; back to FP-0/1 to overwrite the first operand + ; with zero for return value. + +; ----------------------------- +; Handle string AND number (10) +; ----------------------------- +; e.g. "YOU WIN" AND SCORE>99 will return the string if condition is true +; or the null string if false. + +;; str-&-no +L1AF8: LD A,(DE) ; fetch exponent of second number. + AND A ; test it. + RET NZ ; return if number was not zero - the string + ; is the result. + +; if the number was zero (false) then the null string must be returned by +; altering the length of the string on the calculator stack to zero. + + PUSH DE ; save pointer to the now obsolete number + ; (which will become the new STKEND) + + DEC DE ; point to the 5th byte of string descriptor. + XOR A ; clear the accumulator. + LD (DE),A ; place zero in high byte of length. + DEC DE ; address low byte of length. + LD (DE),A ; place zero there - now the null string. + + POP DE ; restore pointer - new STKEND. + RET ; return. + +; ----------------------------------- +; Perform comparison ($09-$0E, $11-$16) +; ----------------------------------- +; True binary operations. +; +; A single entry point is used to evaluate six numeric and six string +; comparisons. On entry, the calculator literal is in the B register and +; the two numeric values, or the two string parameters, are on the +; calculator stack. +; The individual bits of the literal are manipulated to group similar +; operations although the SUB 8 instruction does nothing useful and merely +; alters the string test bit. +; Numbers are compared by subtracting one from the other, strings are +; compared by comparing every character until a mismatch, or the end of one +; or both, is reached. +; +; Numeric Comparisons. +; -------------------- +; The 'x>y' example is the easiest as it employs straight-thru logic. +; Number y is subtracted from x and the result tested for greater-0 yielding +; a final value 1 (true) or 0 (false). +; For 'x0? NOT +; no-gr-eql x>=y 0A 00000010 dec 00000001 10000000c swap y-x ? --- >0? NOT +; nos-neql x<>y 0B 00000011 dec 00000010 00000001 ---- x-y ? NOT --- NOT +; no-grtr x>y 0C 00000100 - 00000100 00000010 ---- x-y ? --- >0? --- +; no-less x0? --- +; nos-eql x=y 0E 00000110 - 00000110 00000011 ---- x-y ? NOT --- --- +; +; comp -> C/F +; ==== === +; str-l-eql x$<=y$ 11 00001001 dec 00001000 00000100 ---- x$y$ 0 !or >0? NOT +; str-gr-eql x$>=y$ 12 00001010 dec 00001001 10000100c swap y$x$ 0 !or >0? NOT +; strs-neql x$<>y$ 13 00001011 dec 00001010 00000101 ---- x$y$ 0 !or >0? NOT +; str-grtr x$>y$ 14 00001100 - 00001100 00000110 ---- x$y$ 0 !or >0? --- +; str-less x$0? --- +; strs-eql x$=y$ 16 00001110 - 00001110 00000111 ---- x$y$ 0 !or >0? --- +; +; String comparisons are a little different in that the eql/neql carry flag +; from the 2nd RRCA is, as before, fed into the first of the end tests but +; along the way it gets modified by the comparison process. The result on the +; stack always starts off as zero and the carry fed in determines if NOT is +; applied to it. So the only time the greater-0 test is applied is if the +; stack holds zero which is not very efficient as the test will always yield +; zero. The most likely explanation is that there were once separate end tests +; for numbers and strings. + +;; no-l-eql,etc. +L1B03: LD A,B ; transfer literal to accumulator. + SUB $08 ; subtract eight - which is not useful. + + BIT 2,A ; isolate '>', '<', '='. + + JR NZ,L1B0B ; skip to EX-OR-NOT with these. + + DEC A ; else make $00-$02, $08-$0A to match bits 0-2. + +;; EX-OR-NOT +L1B0B: RRCA ; the first RRCA sets carry for a swap. + JR NC,L1B16 ; forward to NU-OR-STR with other 8 cases + +; for the other 4 cases the two values on the calculator stack are exchanged. + + PUSH AF ; save A and carry. + PUSH HL ; save HL - pointer to first operand. + ; (DE points to second operand). + + CALL L1A72 ; routine exchange swaps the two values. + ; (HL = second operand, DE = STKEND) + + POP DE ; DE = first operand + EX DE,HL ; as we were. + POP AF ; restore A and carry. + +; Note. it would be better if the 2nd RRCA preceded the string test. +; It would save two duplicate bytes and if we also got rid of that sub 8 +; at the beginning we wouldn't have to alter which bit we test. + +;; NU-OR-STR +L1B16: BIT 2,A ; test if a string comparison. + JR NZ,L1B21 ; forward to STRINGS if so. + +; continue with numeric comparisons. + + RRCA ; 2nd RRCA causes eql/neql to set carry. + PUSH AF ; save A and carry + + CALL L174C ; routine subtract leaves result on stack. + JR L1B54 ; forward to END-TESTS + +; --- + +;; STRINGS +L1B21: RRCA ; 2nd RRCA causes eql/neql to set carry. + PUSH AF ; save A and carry. + + CALL L13F8 ; routine STK-FETCH gets 2nd string params + PUSH DE ; save start2 *. + PUSH BC ; and the length. + + CALL L13F8 ; routine STK-FETCH gets 1st string + ; parameters - start in DE, length in BC. + POP HL ; restore length of second to HL. + +; A loop is now entered to compare, by subtraction, each corresponding character +; of the strings. For each successful match, the pointers are incremented and +; the lengths decreased and the branch taken back to here. If both string +; remainders become null at the same time, then an exact match exists. + +;; BYTE-COMP +L1B2C: LD A,H ; test if the second string + OR L ; is the null string and hold flags. + + EX (SP),HL ; put length2 on stack, bring start2 to HL *. + LD A,B ; hi byte of length1 to A + + JR NZ,L1B3D ; forward to SEC-PLUS if second not null. + + OR C ; test length of first string. + +;; SECND-LOW +L1B33: POP BC ; pop the second length off stack. + JR Z,L1B3A ; forward to BOTH-NULL if first string is also + ; of zero length. + +; the true condition - first is longer than second (SECND-LESS) + + POP AF ; restore carry (set if eql/neql) + CCF ; complement carry flag. + ; Note. equality becomes false. + ; Inequality is true. By swapping or applying + ; a terminal 'not', all comparisons have been + ; manipulated so that this is success path. + JR L1B50 ; forward to leave via STR-TEST + +; --- +; the branch was here with a match + +;; BOTH-NULL +L1B3A: POP AF ; restore carry - set for eql/neql + JR L1B50 ; forward to STR-TEST + +; --- +; the branch was here when 2nd string not null and low byte of first is yet +; to be tested. + + +;; SEC-PLUS +L1B3D: OR C ; test the length of first string. + JR Z,L1B4D ; forward to FRST-LESS if length is zero. + +; both strings have at least one character left. + + LD A,(DE) ; fetch character of first string. + SUB (HL) ; subtract with that of 2nd string. + JR C,L1B4D ; forward to FRST-LESS if carry set + + JR NZ,L1B33 ; back to SECND-LOW and then STR-TEST + ; if not exact match. + + DEC BC ; decrease length of 1st string. + INC DE ; increment 1st string pointer. + + INC HL ; increment 2nd string pointer. + EX (SP),HL ; swap with length on stack + DEC HL ; decrement 2nd string length + JR L1B2C ; back to BYTE-COMP + +; --- +; the false condition. + +;; FRST-LESS +L1B4D: POP BC ; discard length + POP AF ; pop A + AND A ; clear the carry for false result. + +; --- +; exact match and x$>y$ rejoin here + +;; STR-TEST +L1B50: PUSH AF ; save A and carry + + RST 28H ;; FP-CALC + DEFB $A0 ;;stk-zero an initial false value. + DEFB $34 ;;end-calc + +; both numeric and string paths converge here. + +;; END-TESTS +L1B54: POP AF ; pop carry - will be set if eql/neql + PUSH AF ; save it again. + + CALL C,L1AD5 ; routine NOT sets true(1) if equal(0) + ; or, for strings, applies true result. + CALL L1ACE ; greater-0 ?????????? + + + POP AF ; pop A + RRCA ; the third RRCA - test for '<=', '>=' or '<>'. + CALL NC,L1AD5 ; apply a terminal NOT if so. + RET ; return. + +; ------------------------- +; String concatenation ($17) +; ------------------------- +; This literal combines two strings into one e.g. LET A$ = B$ + C$ +; The two parameters of the two strings to be combined are on the stack. + +;; strs-add +L1B62: CALL L13F8 ; routine STK-FETCH fetches string parameters + ; and deletes calculator stack entry. + PUSH DE ; save start address. + PUSH BC ; and length. + + CALL L13F8 ; routine STK-FETCH for first string + POP HL ; re-fetch first length + PUSH HL ; and save again + PUSH DE ; save start of second string + PUSH BC ; and its length. + + ADD HL,BC ; add the two lengths. + LD B,H ; transfer to BC + LD C,L ; and create + RST 30H ; BC-SPACES in workspace. + ; DE points to start of space. + + CALL L12C3 ; routine STK-STO-$ stores parameters + ; of new string updating STKEND. + + POP BC ; length of first + POP HL ; address of start + LD A,B ; test for + OR C ; zero length. + JR Z,L1B7D ; to OTHER-STR if null string + + LDIR ; copy string to workspace. + +;; OTHER-STR +L1B7D: POP BC ; now second length + POP HL ; and start of string + LD A,B ; test this one + OR C ; for zero length + JR Z,L1B85 ; skip forward to STK-PNTRS if so as complete. + + LDIR ; else copy the bytes. + ; and continue into next routine which + ; sets the calculator stack pointers. + +; -------------------- +; Check stack pointers +; -------------------- +; Register DE is set to STKEND and HL, the result pointer, is set to five +; locations below this. +; This routine is used when it is inconvenient to save these values at the +; time the calculator stack is manipulated due to other activity on the +; machine stack. +; This routine is also used to terminate the VAL routine for +; the same reason and to initialize the calculator stack at the start of +; the CALCULATE routine. + +;; STK-PNTRS +L1B85: LD HL,($401C) ; fetch STKEND value from system variable. + LD DE,$FFFB ; the value -5 + PUSH HL ; push STKEND value. + + ADD HL,DE ; subtract 5 from HL. + + POP DE ; pop STKEND to DE. + RET ; return. + +; ---------------- +; Handle CHR$ (2B) +; ---------------- +; This function returns a single character string that is a result of +; converting a number in the range 0-255 to a string e.g. CHR$ 38 = "A". +; Note. the ZX81 does not have an ASCII character set. + +;; chrs +L1B8F: CALL L15CD ; routine FP-TO-A puts the number in A. + + JR C,L1BA2 ; forward to REPORT-Bd if overflow + JR NZ,L1BA2 ; forward to REPORT-Bd if negative + + PUSH AF ; save the argument. + + LD BC,$0001 ; one space required. + RST 30H ; BC-SPACES makes DE point to start + + POP AF ; restore the number. + + LD (DE),A ; and store in workspace + + CALL L12C3 ; routine STK-STO-$ stacks descriptor. + + EX DE,HL ; make HL point to result and DE to STKEND. + RET ; return. + +; --- + +;; REPORT-Bd +L1BA2: RST 08H ; ERROR-1 + DEFB $0A ; Error Report: Integer out of range + +; ---------------------------- +; Handle VAL ($1A) +; ---------------------------- +; VAL treats the characters in a string as a numeric expression. +; e.g. VAL "2.3" = 2.3, VAL "2+4" = 6, VAL ("2" + "4") = 24. + +;; val +L1BA4: LD HL,($4016) ; fetch value of system variable CH_ADD + PUSH HL ; and save on the machine stack. + + CALL L13F8 ; routine STK-FETCH fetches the string operand + ; from calculator stack. + + PUSH DE ; save the address of the start of the string. + INC BC ; increment the length for a carriage return. + + RST 30H ; BC-SPACES creates the space in workspace. + POP HL ; restore start of string to HL. + LD ($4016),DE ; load CH_ADD with start DE in workspace. + + PUSH DE ; save the start in workspace + LDIR ; copy string from program or variables or + ; workspace to the workspace area. + EX DE,HL ; end of string + 1 to HL + DEC HL ; decrement HL to point to end of new area. + LD (HL),$76 ; insert a carriage return at end. + ; ZX81 has a non-ASCII character set + RES 7,(IY+$01) ; update FLAGS - signal checking syntax. + CALL L0D92 ; routine CLASS-06 - SCANNING evaluates string + ; expression and checks for integer result. + + CALL L0D22 ; routine CHECK-2 checks for carriage return. + + + POP HL ; restore start of string in workspace. + + LD ($4016),HL ; set CH_ADD to the start of the string again. + SET 7,(IY+$01) ; update FLAGS - signal running program. + CALL L0F55 ; routine SCANNING evaluates the string + ; in full leaving result on calculator stack. + + POP HL ; restore saved character address in program. + LD ($4016),HL ; and reset the system variable CH_ADD. + + JR L1B85 ; back to exit via STK-PNTRS. + ; resetting the calculator stack pointers + ; HL and DE from STKEND as it wasn't possible + ; to preserve them during this routine. + +; ---------------- +; Handle STR$ (2A) +; ---------------- +; This function returns a string representation of a numeric argument. +; The method used is to trick the PRINT-FP routine into thinking it +; is writing to a collapsed display file when in fact it is writing to +; string workspace. +; If there is already a newline at the intended print position and the +; column count has not been reduced to zero then the print routine +; assumes that there is only 1K of RAM and the screen memory, like the rest +; of dynamic memory, expands as necessary using calls to the ONE-SPACE +; routine. The screen is character-mapped not bit-mapped. + +;; str$ +L1BD5: LD BC,$0001 ; create an initial byte in workspace + RST 30H ; using BC-SPACES restart. + + LD (HL),$76 ; place a carriage return there. + + LD HL,($4039) ; fetch value of S_POSN column/line + PUSH HL ; and preserve on stack. + + LD L,$FF ; make column value high to create a + ; contrived buffer of length 254. + LD ($4039),HL ; and store in system variable S_POSN. + + LD HL,($400E) ; fetch value of DF_CC + PUSH HL ; and preserve on stack also. + + LD ($400E),DE ; now set DF_CC which normally addresses + ; somewhere in the display file to the start + ; of workspace. + PUSH DE ; save the start of new string. + + CALL L15DB ; routine PRINT-FP. + + POP DE ; retrieve start of string. + + LD HL,($400E) ; fetch end of string from DF_CC. + AND A ; prepare for true subtraction. + SBC HL,DE ; subtract to give length. + + LD B,H ; and transfer to the BC + LD C,L ; register. + + POP HL ; restore original + LD ($400E),HL ; DF_CC value + + POP HL ; restore original + LD ($4039),HL ; S_POSN values. + + CALL L12C3 ; routine STK-STO-$ stores the string + ; descriptor on the calculator stack. + + EX DE,HL ; HL = last value, DE = STKEND. + RET ; return. + + +; ------------------- +; THE 'CODE' FUNCTION +; ------------------- +; (offset $19: 'code') +; Returns the code of a character or first character of a string +; e.g. CODE "AARDVARK" = 38 (not 65 as the ZX81 does not have an ASCII +; character set). + + +;; code +L1C06: CALL L13F8 ; routine STK-FETCH to fetch and delete the + ; string parameters. + ; DE points to the start, BC holds the length. + LD A,B ; test length + OR C ; of the string. + JR Z,L1C0E ; skip to STK-CODE with zero if the null string. + + LD A,(DE) ; else fetch the first character. + +;; STK-CODE +L1C0E: JP L151D ; jump back to STACK-A (with memory check) + +; -------------------- +; THE 'LEN' SUBROUTINE +; -------------------- +; (offset $1b: 'len') +; Returns the length of a string. +; In Sinclair BASIC strings can be more than twenty thousand characters long +; so a sixteen-bit register is required to store the length + +;; len +L1C11: CALL L13F8 ; routine STK-FETCH to fetch and delete the + ; string parameters from the calculator stack. + ; register BC now holds the length of string. + + JP L1520 ; jump back to STACK-BC to save result on the + ; calculator stack (with memory check). + +; ------------------------------------- +; THE 'DECREASE THE COUNTER' SUBROUTINE +; ------------------------------------- +; (offset $31: 'dec-jr-nz') +; The calculator has an instruction that decrements a single-byte +; pseudo-register and makes consequential relative jumps just like +; the Z80's DJNZ instruction. + +;; dec-jr-nz +L1C17: EXX ; switch in set that addresses code + + PUSH HL ; save pointer to offset byte + LD HL,$401E ; address BREG in system variables + DEC (HL) ; decrement it + POP HL ; restore pointer + + JR NZ,L1C24 ; to JUMP-2 if not zero + + INC HL ; step past the jump length. + EXX ; switch in the main set. + RET ; return. + +; Note. as a general rule the calculator avoids using the IY register +; otherwise the cumbersome 4 instructions in the middle could be replaced by +; dec (iy+$xx) - using three instruction bytes instead of six. + + +; --------------------- +; THE 'JUMP' SUBROUTINE +; --------------------- +; (Offset $2F; 'jump') +; This enables the calculator to perform relative jumps just like +; the Z80 chip's JR instruction. +; This is one of the few routines to be polished for the ZX Spectrum. +; See, without looking at the ZX Spectrum ROM, if you can get rid of the +; relative jump. + +;; jump +;; JUMP +L1C23: EXX ;switch in pointer set + +;; JUMP-2 +L1C24: LD E,(HL) ; the jump byte 0-127 forward, 128-255 back. + XOR A ; clear accumulator. + BIT 7,E ; test if negative jump + JR Z,L1C2B ; skip, if positive, to JUMP-3. + + CPL ; else change to $FF. + +;; JUMP-3 +L1C2B: LD D,A ; transfer to high byte. + ADD HL,DE ; advance calculator pointer forward or back. + + EXX ; switch out pointer set. + RET ; return. + +; ----------------------------- +; THE 'JUMP ON TRUE' SUBROUTINE +; ----------------------------- +; (Offset $00; 'jump-true') +; This enables the calculator to perform conditional relative jumps +; dependent on whether the last test gave a true result +; On the ZX81, the exponent will be zero for zero or else $81 for one. + +;; jump-true +L1C2F: LD A,(DE) ; collect exponent byte + + AND A ; is result 0 or 1 ? + JR NZ,L1C23 ; back to JUMP if true (1). + + EXX ; else switch in the pointer set. + INC HL ; step past the jump length. + EXX ; switch in the main set. + RET ; return. + + +; ------------------------ +; THE 'MODULUS' SUBROUTINE +; ------------------------ +; ( Offset $2E: 'n-mod-m' ) +; ( i1, i2 -- i3, i4 ) +; The subroutine calculate N mod M where M is the positive integer, the +; 'last value' on the calculator stack and N is the integer beneath. +; The subroutine returns the integer quotient as the last value and the +; remainder as the value beneath. +; e.g. 17 MOD 3 = 5 remainder 2 +; It is invoked during the calculation of a random number and also by +; the PRINT-FP routine. + +;; n-mod-m +L1C37: RST 28H ;; FP-CALC 17, 3. + DEFB $C0 ;;st-mem-0 17, 3. + DEFB $02 ;;delete 17. + DEFB $2D ;;duplicate 17, 17. + DEFB $E0 ;;get-mem-0 17, 17, 3. + DEFB $05 ;;division 17, 17/3. + DEFB $24 ;;int 17, 5. + DEFB $E0 ;;get-mem-0 17, 5, 3. + DEFB $01 ;;exchange 17, 3, 5. + DEFB $C0 ;;st-mem-0 17, 3, 5. + DEFB $04 ;;multiply 17, 15. + DEFB $03 ;;subtract 2. + DEFB $E0 ;;get-mem-0 2, 5. + DEFB $34 ;;end-calc 2, 5. + + RET ; return. + + +; ---------------------- +; THE 'INTEGER' FUNCTION +; ---------------------- +; (offset $24: 'int') +; This function returns the integer of x, which is just the same as truncate +; for positive numbers. The truncate literal truncates negative numbers +; upwards so that -3.4 gives -3 whereas the BASIC INT function has to +; truncate negative numbers down so that INT -3.4 is 4. +; It is best to work through using, say, plus or minus 3.4 as examples. + +;; int +L1C46: RST 28H ;; FP-CALC x. (= 3.4 or -3.4). + DEFB $2D ;;duplicate x, x. + DEFB $32 ;;less-0 x, (1/0) + DEFB $00 ;;jump-true x, (1/0) + DEFB $04 ;;to L1C46, X-NEG + + DEFB $36 ;;truncate trunc 3.4 = 3. + DEFB $34 ;;end-calc 3. + + RET ; return with + int x on stack. + + +;; X-NEG +L1C4E: DEFB $2D ;;duplicate -3.4, -3.4. + DEFB $36 ;;truncate -3.4, -3. + DEFB $C0 ;;st-mem-0 -3.4, -3. + DEFB $03 ;;subtract -.4 + DEFB $E0 ;;get-mem-0 -.4, -3. + DEFB $01 ;;exchange -3, -.4. + DEFB $2C ;;not -3, (0). + DEFB $00 ;;jump-true -3. + DEFB $03 ;;to L1C59, EXIT -3. + + DEFB $A1 ;;stk-one -3, 1. + DEFB $03 ;;subtract -4. + +;; EXIT +L1C59: DEFB $34 ;;end-calc -4. + + RET ; return. + + +; ---------------- +; Exponential (23) +; ---------------- +; +; + +;; EXP +;; exp +L1C5B: RST 28H ;; FP-CALC + DEFB $30 ;;stk-data + DEFB $F1 ;;Exponent: $81, Bytes: 4 + DEFB $38,$AA,$3B,$29 ;; + DEFB $04 ;;multiply + DEFB $2D ;;duplicate + DEFB $24 ;;int + DEFB $C3 ;;st-mem-3 + DEFB $03 ;;subtract + DEFB $2D ;;duplicate + DEFB $0F ;;addition + DEFB $A1 ;;stk-one + DEFB $03 ;;subtract + DEFB $88 ;;series-08 + DEFB $13 ;;Exponent: $63, Bytes: 1 + DEFB $36 ;;(+00,+00,+00) + DEFB $58 ;;Exponent: $68, Bytes: 2 + DEFB $65,$66 ;;(+00,+00) + DEFB $9D ;;Exponent: $6D, Bytes: 3 + DEFB $78,$65,$40 ;;(+00) + DEFB $A2 ;;Exponent: $72, Bytes: 3 + DEFB $60,$32,$C9 ;;(+00) + DEFB $E7 ;;Exponent: $77, Bytes: 4 + DEFB $21,$F7,$AF,$24 ;; + DEFB $EB ;;Exponent: $7B, Bytes: 4 + DEFB $2F,$B0,$B0,$14 ;; + DEFB $EE ;;Exponent: $7E, Bytes: 4 + DEFB $7E,$BB,$94,$58 ;; + DEFB $F1 ;;Exponent: $81, Bytes: 4 + DEFB $3A,$7E,$F8,$CF ;; + DEFB $E3 ;;get-mem-3 + DEFB $34 ;;end-calc + + CALL L15CD ; routine FP-TO-A + JR NZ,L1C9B ; to N-NEGTV + + JR C,L1C99 ; to REPORT-6b + + ADD A,(HL) ; + JR NC,L1CA2 ; to RESULT-OK + + +;; REPORT-6b +L1C99: RST 08H ; ERROR-1 + DEFB $05 ; Error Report: Number too big + +;; N-NEGTV +L1C9B: JR C,L1CA4 ; to RSLT-ZERO + + SUB (HL) ; + JR NC,L1CA4 ; to RSLT-ZERO + + NEG ; Negate + +;; RESULT-OK +L1CA2: LD (HL),A ; + RET ; return. + + +;; RSLT-ZERO +L1CA4: RST 28H ;; FP-CALC + DEFB $02 ;;delete + DEFB $A0 ;;stk-zero + DEFB $34 ;;end-calc + + RET ; return. + + +; -------------------------------- +; THE 'NATURAL LOGARITHM' FUNCTION +; -------------------------------- +; (offset $22: 'ln') +; Like the ZX81 itself, 'natural' logarithms came from Scotland. +; They were devised in 1614 by well-traveled Scotsman John Napier who noted +; "Nothing doth more molest and hinder calculators than the multiplications, +; divisions, square and cubical extractions of great numbers". +; +; Napier's logarithms enabled the above operations to be accomplished by +; simple addition and subtraction simplifying the navigational and +; astronomical calculations which beset his age. +; Napier's logarithms were quickly overtaken by logarithms to the base 10 +; devised, in conjunction with Napier, by Henry Briggs a Cambridge-educated +; professor of Geometry at Oxford University. These simplified the layout +; of the tables enabling humans to easily scale calculations. +; +; It is only recently with the introduction of pocket calculators and +; computers like the ZX81 that natural logarithms are once more at the fore, +; although some computers retain logarithms to the base ten. +; 'Natural' logarithms are powers to the base 'e', which like 'pi' is a +; naturally occurring number in branches of mathematics. +; Like 'pi' also, 'e' is an irrational number and starts 2.718281828... +; +; The tabular use of logarithms was that to multiply two numbers one looked +; up their two logarithms in the tables, added them together and then looked +; for the result in a table of antilogarithms to give the desired product. +; +; The EXP function is the BASIC equivalent of a calculator's 'antiln' function +; and by picking any two numbers, 1.72 and 6.89 say, +; 10 PRINT EXP ( LN 1.72 + LN 6.89 ) +; will give just the same result as +; 20 PRINT 1.72 * 6.89. +; Division is accomplished by subtracting the two logs. +; +; Napier also mentioned "square and cubicle extractions". +; To raise a number to the power 3, find its 'ln', multiply by 3 and find the +; 'antiln'. e.g. PRINT EXP( LN 4 * 3 ) gives 64. +; Similarly to find the n'th root divide the logarithm by 'n'. +; The ZX81 ROM used PRINT EXP ( LN 9 / 2 ) to find the square root of the +; number 9. The Napieran square root function is just a special case of +; the 'to_power' function. A cube root or indeed any root/power would be just +; as simple. + +; First test that the argument to LN is a positive, non-zero number. + +;; ln +L1CA9: RST 28H ;; FP-CALC + DEFB $2D ;;duplicate + DEFB $33 ;;greater-0 + DEFB $00 ;;jump-true + DEFB $04 ;;to L1CB1, VALID + + DEFB $34 ;;end-calc + + +;; REPORT-Ab +L1CAF: RST 08H ; ERROR-1 + DEFB $09 ; Error Report: Invalid argument + +;; VALID +L1CB1: DEFB $A0 ;;stk-zero Note. not + DEFB $02 ;;delete necessary. + DEFB $34 ;;end-calc + LD A,(HL) ; + + LD (HL),$80 ; + CALL L151D ; routine STACK-A + + RST 28H ;; FP-CALC + DEFB $30 ;;stk-data + DEFB $38 ;;Exponent: $88, Bytes: 1 + DEFB $00 ;;(+00,+00,+00) + DEFB $03 ;;subtract + DEFB $01 ;;exchange + DEFB $2D ;;duplicate + DEFB $30 ;;stk-data + DEFB $F0 ;;Exponent: $80, Bytes: 4 + DEFB $4C,$CC,$CC,$CD ;; + DEFB $03 ;;subtract + DEFB $33 ;;greater-0 + DEFB $00 ;;jump-true + DEFB $08 ;;to L1CD2, GRE.8 + + DEFB $01 ;;exchange + DEFB $A1 ;;stk-one + DEFB $03 ;;subtract + DEFB $01 ;;exchange + DEFB $34 ;;end-calc + + INC (HL) ; + + RST 28H ;; FP-CALC + +;; GRE.8 +L1CD2: DEFB $01 ;;exchange + DEFB $30 ;;stk-data + DEFB $F0 ;;Exponent: $80, Bytes: 4 + DEFB $31,$72,$17,$F8 ;; + DEFB $04 ;;multiply + DEFB $01 ;;exchange + DEFB $A2 ;;stk-half + DEFB $03 ;;subtract + DEFB $A2 ;;stk-half + DEFB $03 ;;subtract + DEFB $2D ;;duplicate + DEFB $30 ;;stk-data + DEFB $32 ;;Exponent: $82, Bytes: 1 + DEFB $20 ;;(+00,+00,+00) + DEFB $04 ;;multiply + DEFB $A2 ;;stk-half + DEFB $03 ;;subtract + DEFB $8C ;;series-0C + DEFB $11 ;;Exponent: $61, Bytes: 1 + DEFB $AC ;;(+00,+00,+00) + DEFB $14 ;;Exponent: $64, Bytes: 1 + DEFB $09 ;;(+00,+00,+00) + DEFB $56 ;;Exponent: $66, Bytes: 2 + DEFB $DA,$A5 ;;(+00,+00) + DEFB $59 ;;Exponent: $69, Bytes: 2 + DEFB $30,$C5 ;;(+00,+00) + DEFB $5C ;;Exponent: $6C, Bytes: 2 + DEFB $90,$AA ;;(+00,+00) + DEFB $9E ;;Exponent: $6E, Bytes: 3 + DEFB $70,$6F,$61 ;;(+00) + DEFB $A1 ;;Exponent: $71, Bytes: 3 + DEFB $CB,$DA,$96 ;;(+00) + DEFB $A4 ;;Exponent: $74, Bytes: 3 + DEFB $31,$9F,$B4 ;;(+00) + DEFB $E7 ;;Exponent: $77, Bytes: 4 + DEFB $A0,$FE,$5C,$FC ;; + DEFB $EA ;;Exponent: $7A, Bytes: 4 + DEFB $1B,$43,$CA,$36 ;; + DEFB $ED ;;Exponent: $7D, Bytes: 4 + DEFB $A7,$9C,$7E,$5E ;; + DEFB $F0 ;;Exponent: $80, Bytes: 4 + DEFB $6E,$23,$80,$93 ;; + DEFB $04 ;;multiply + DEFB $0F ;;addition + DEFB $34 ;;end-calc + + RET ; return. + +; ----------------------------- +; THE 'TRIGONOMETRIC' FUNCTIONS +; ----------------------------- +; Trigonometry is rocket science. It is also used by carpenters and pyramid +; builders. +; Some uses can be quite abstract but the principles can be seen in simple +; right-angled triangles. Triangles have some special properties - +; +; 1) The sum of the three angles is always PI radians (180 degrees). +; Very helpful if you know two angles and wish to find the third. +; 2) In any right-angled triangle the sum of the squares of the two shorter +; sides is equal to the square of the longest side opposite the right-angle. +; Very useful if you know the length of two sides and wish to know the +; length of the third side. +; 3) Functions sine, cosine and tangent enable one to calculate the length +; of an unknown side when the length of one other side and an angle is +; known. +; 4) Functions arcsin, arccosine and arctan enable one to calculate an unknown +; angle when the length of two of the sides is known. + +; -------------------------------- +; THE 'REDUCE ARGUMENT' SUBROUTINE +; -------------------------------- +; (offset $35: 'get-argt') +; +; This routine performs two functions on the angle, in radians, that forms +; the argument to the sine and cosine functions. +; First it ensures that the angle 'wraps round'. That if a ship turns through +; an angle of, say, 3*PI radians (540 degrees) then the net effect is to turn +; through an angle of PI radians (180 degrees). +; Secondly it converts the angle in radians to a fraction of a right angle, +; depending within which quadrant the angle lies, with the periodicity +; resembling that of the desired sine value. +; The result lies in the range -1 to +1. +; +; 90 deg. +; +; (pi/2) +; II +1 I +; | +; sin+ |\ | /| sin+ +; cos- | \ | / | cos+ +; tan- | \ | / | tan+ +; | \|/) | +; 180 deg. (pi) 0 -|----+----|-- 0 (0) 0 degrees +; | /|\ | +; sin- | / | \ | sin- +; cos- | / | \ | cos+ +; tan+ |/ | \| tan- +; | +; III -1 IV +; (3pi/2) +; +; 270 deg. + + +;; get-argt +L1D18: RST 28H ;; FP-CALC X. + DEFB $30 ;;stk-data + DEFB $EE ;;Exponent: $7E, + ;;Bytes: 4 + DEFB $22,$F9,$83,$6E ;; X, 1/(2*PI) + DEFB $04 ;;multiply X/(2*PI) = fraction + + DEFB $2D ;;duplicate + DEFB $A2 ;;stk-half + DEFB $0F ;;addition + DEFB $24 ;;int + + DEFB $03 ;;subtract now range -.5 to .5 + + DEFB $2D ;;duplicate + DEFB $0F ;;addition now range -1 to 1. + DEFB $2D ;;duplicate + DEFB $0F ;;addition now range -2 to 2. + +; quadrant I (0 to +1) and quadrant IV (-1 to 0) are now correct. +; quadrant II ranges +1 to +2. +; quadrant III ranges -2 to -1. + + DEFB $2D ;;duplicate Y, Y. + DEFB $27 ;;abs Y, abs(Y). range 1 to 2 + DEFB $A1 ;;stk-one Y, abs(Y), 1. + DEFB $03 ;;subtract Y, abs(Y)-1. range 0 to 1 + DEFB $2D ;;duplicate Y, Z, Z. + DEFB $33 ;;greater-0 Y, Z, (1/0). + + DEFB $C0 ;;st-mem-0 store as possible sign + ;; for cosine function. + + DEFB $00 ;;jump-true + DEFB $04 ;;to L1D35, ZPLUS with quadrants II and III + +; else the angle lies in quadrant I or IV and value Y is already correct. + + DEFB $02 ;;delete Y delete test value. + DEFB $34 ;;end-calc Y. + + RET ; return. with Q1 and Q4 >>> + +; The branch was here with quadrants II (0 to 1) and III (1 to 0). +; Y will hold -2 to -1 if this is quadrant III. + +;; ZPLUS +L1D35: DEFB $A1 ;;stk-one Y, Z, 1 + DEFB $03 ;;subtract Y, Z-1. Q3 = 0 to -1 + DEFB $01 ;;exchange Z-1, Y. + DEFB $32 ;;less-0 Z-1, (1/0). + DEFB $00 ;;jump-true Z-1. + DEFB $02 ;;to L1D3C, YNEG + ;;if angle in quadrant III + +; else angle is within quadrant II (-1 to 0) + + DEFB $18 ;;negate range +1 to 0 + + +;; YNEG +L1D3C: DEFB $34 ;;end-calc quadrants II and III correct. + + RET ; return. + + +; --------------------- +; THE 'COSINE' FUNCTION +; --------------------- +; (offset $1D: 'cos') +; Cosines are calculated as the sine of the opposite angle rectifying the +; sign depending on the quadrant rules. +; +; +; /| +; h /y| +; / |o +; /x | +; /----| +; a +; +; The cosine of angle x is the adjacent side (a) divided by the hypotenuse 1. +; However if we examine angle y then a/h is the sine of that angle. +; Since angle x plus angle y equals a right-angle, we can find angle y by +; subtracting angle x from pi/2. +; However it's just as easy to reduce the argument first and subtract the +; reduced argument from the value 1 (a reduced right-angle). +; It's even easier to subtract 1 from the angle and rectify the sign. +; In fact, after reducing the argument, the absolute value of the argument +; is used and rectified using the test result stored in mem-0 by 'get-argt' +; for that purpose. + +;; cos +L1D3E: RST 28H ;; FP-CALC angle in radians. + DEFB $35 ;;get-argt X reduce -1 to +1 + + DEFB $27 ;;abs ABS X 0 to 1 + DEFB $A1 ;;stk-one ABS X, 1. + DEFB $03 ;;subtract now opposite angle + ;; though negative sign. + DEFB $E0 ;;get-mem-0 fetch sign indicator. + DEFB $00 ;;jump-true + DEFB $06 ;;fwd to L1D4B, C-ENT + ;;forward to common code if in QII or QIII + + + DEFB $18 ;;negate else make positive. + DEFB $2F ;;jump + DEFB $03 ;;fwd to L1D4B, C-ENT + ;;with quadrants QI and QIV + +; ------------------- +; THE 'SINE' FUNCTION +; ------------------- +; (offset $1C: 'sin') +; This is a fundamental transcendental function from which others such as cos +; and tan are directly, or indirectly, derived. +; It uses the series generator to produce Chebyshev polynomials. +; +; +; /| +; 1 / | +; / |x +; /a | +; /----| +; y +; +; The 'get-argt' function is designed to modify the angle and its sign +; in line with the desired sine value and afterwards it can launch straight +; into common code. + +;; sin +L1D49: RST 28H ;; FP-CALC angle in radians + DEFB $35 ;;get-argt reduce - sign now correct. + +;; C-ENT +L1D4B: DEFB $2D ;;duplicate + DEFB $2D ;;duplicate + DEFB $04 ;;multiply + DEFB $2D ;;duplicate + DEFB $0F ;;addition + DEFB $A1 ;;stk-one + DEFB $03 ;;subtract + + DEFB $86 ;;series-06 + DEFB $14 ;;Exponent: $64, Bytes: 1 + DEFB $E6 ;;(+00,+00,+00) + DEFB $5C ;;Exponent: $6C, Bytes: 2 + DEFB $1F,$0B ;;(+00,+00) + DEFB $A3 ;;Exponent: $73, Bytes: 3 + DEFB $8F,$38,$EE ;;(+00) + DEFB $E9 ;;Exponent: $79, Bytes: 4 + DEFB $15,$63,$BB,$23 ;; + DEFB $EE ;;Exponent: $7E, Bytes: 4 + DEFB $92,$0D,$CD,$ED ;; + DEFB $F1 ;;Exponent: $81, Bytes: 4 + DEFB $23,$5D,$1B,$EA ;; + + DEFB $04 ;;multiply + DEFB $34 ;;end-calc + + RET ; return. + + +; ---------------------- +; THE 'TANGENT' FUNCTION +; ---------------------- +; (offset $1E: 'tan') +; +; Evaluates tangent x as sin(x) / cos(x). +; +; +; /| +; h / | +; / |o +; /x | +; /----| +; a +; +; The tangent of angle x is the ratio of the length of the opposite side +; divided by the length of the adjacent side. As the opposite length can +; be calculates using sin(x) and the adjacent length using cos(x) then +; the tangent can be defined in terms of the previous two functions. + +; Error 6 if the argument, in radians, is too close to one like pi/2 +; which has an infinite tangent. e.g. PRINT TAN (PI/2) evaluates as 1/0. +; Similarly PRINT TAN (3*PI/2), TAN (5*PI/2) etc. + +;; tan +L1D6E: RST 28H ;; FP-CALC x. + DEFB $2D ;;duplicate x, x. + DEFB $1C ;;sin x, sin x. + DEFB $01 ;;exchange sin x, x. + DEFB $1D ;;cos sin x, cos x. + DEFB $05 ;;division sin x/cos x (= tan x). + DEFB $34 ;;end-calc tan x. + + RET ; return. + +; --------------------- +; THE 'ARCTAN' FUNCTION +; --------------------- +; (Offset $21: 'atn') +; The inverse tangent function with the result in radians. +; This is a fundamental transcendental function from which others such as +; asn and acs are directly, or indirectly, derived. +; It uses the series generator to produce Chebyshev polynomials. + +;; atn +L1D76: LD A,(HL) ; fetch exponent + CP $81 ; compare to that for 'one' + JR C,L1D89 ; forward, if less, to SMALL + + RST 28H ;; FP-CALC X. + DEFB $A1 ;;stk-one + DEFB $18 ;;negate + DEFB $01 ;;exchange + DEFB $05 ;;division + DEFB $2D ;;duplicate + DEFB $32 ;;less-0 + DEFB $A3 ;;stk-pi/2 + DEFB $01 ;;exchange + DEFB $00 ;;jump-true + DEFB $06 ;;to L1D8B, CASES + + DEFB $18 ;;negate + DEFB $2F ;;jump + DEFB $03 ;;to L1D8B, CASES + +; --- + +;; SMALL +L1D89: RST 28H ;; FP-CALC + DEFB $A0 ;;stk-zero + +;; CASES +L1D8B: DEFB $01 ;;exchange + DEFB $2D ;;duplicate + DEFB $2D ;;duplicate + DEFB $04 ;;multiply + DEFB $2D ;;duplicate + DEFB $0F ;;addition + DEFB $A1 ;;stk-one + DEFB $03 ;;subtract + + DEFB $8C ;;series-0C + DEFB $10 ;;Exponent: $60, Bytes: 1 + DEFB $B2 ;;(+00,+00,+00) + DEFB $13 ;;Exponent: $63, Bytes: 1 + DEFB $0E ;;(+00,+00,+00) + DEFB $55 ;;Exponent: $65, Bytes: 2 + DEFB $E4,$8D ;;(+00,+00) + DEFB $58 ;;Exponent: $68, Bytes: 2 + DEFB $39,$BC ;;(+00,+00) + DEFB $5B ;;Exponent: $6B, Bytes: 2 + DEFB $98,$FD ;;(+00,+00) + DEFB $9E ;;Exponent: $6E, Bytes: 3 + DEFB $00,$36,$75 ;;(+00) + DEFB $A0 ;;Exponent: $70, Bytes: 3 + DEFB $DB,$E8,$B4 ;;(+00) + DEFB $63 ;;Exponent: $73, Bytes: 2 + DEFB $42,$C4 ;;(+00,+00) + DEFB $E6 ;;Exponent: $76, Bytes: 4 + DEFB $B5,$09,$36,$BE ;; + DEFB $E9 ;;Exponent: $79, Bytes: 4 + DEFB $36,$73,$1B,$5D ;; + DEFB $EC ;;Exponent: $7C, Bytes: 4 + DEFB $D8,$DE,$63,$BE ;; + DEFB $F0 ;;Exponent: $80, Bytes: 4 + DEFB $61,$A1,$B3,$0C ;; + + DEFB $04 ;;multiply + DEFB $0F ;;addition + DEFB $34 ;;end-calc + + RET ; return. + + +; --------------------- +; THE 'ARCSIN' FUNCTION +; --------------------- +; (Offset $1F: 'asn') +; The inverse sine function with result in radians. +; Derived from arctan function above. +; Error A unless the argument is between -1 and +1 inclusive. +; Uses an adaptation of the formula asn(x) = atn(x/sqr(1-x*x)) +; +; +; /| +; / | +; 1/ |x +; /a | +; /----| +; y +; +; e.g. We know the opposite side (x) and hypotenuse (1) +; and we wish to find angle a in radians. +; We can derive length y by Pythagoras and then use ATN instead. +; Since y*y + x*x = 1*1 (Pythagoras Theorem) then +; y=sqr(1-x*x) - no need to multiply 1 by itself. +; So, asn(a) = atn(x/y) +; or more fully, +; asn(a) = atn(x/sqr(1-x*x)) + +; Close but no cigar. + +; While PRINT ATN (x/SQR (1-x*x)) gives the same results as PRINT ASN x, +; it leads to division by zero when x is 1 or -1. +; To overcome this, 1 is added to y giving half the required angle and the +; result is then doubled. +; That is, PRINT ATN (x/(SQR (1-x*x) +1)) *2 +; +; +; . /| +; . c/ | +; . /1 |x +; . c b /a | +; ---------/----| +; 1 y +; +; By creating an isosceles triangle with two equal sides of 1, angles c and +; c are also equal. If b+c+d = 180 degrees and b+a = 180 degrees then c=a/2. +; +; A value higher than 1 gives the required error as attempting to find the +; square root of a negative number generates an error in Sinclair BASIC. + +;; asn +L1DC4: RST 28H ;; FP-CALC x. + DEFB $2D ;;duplicate x, x. + DEFB $2D ;;duplicate x, x, x. + DEFB $04 ;;multiply x, x*x. + DEFB $A1 ;;stk-one x, x*x, 1. + DEFB $03 ;;subtract x, x*x-1. + DEFB $18 ;;negate x, 1-x*x. + DEFB $25 ;;sqr x, sqr(1-x*x) = y. + DEFB $A1 ;;stk-one x, y, 1. + DEFB $0F ;;addition x, y+1. + DEFB $05 ;;division x/y+1. + DEFB $21 ;;atn a/2 (half the angle) + DEFB $2D ;;duplicate a/2, a/2. + DEFB $0F ;;addition a. + DEFB $34 ;;end-calc a. + + RET ; return. + + +; ------------------------ +; THE 'ARCCOS' FUNCTION +; ------------------------ +; (Offset $20: 'acs') +; The inverse cosine function with the result in radians. +; Error A unless the argument is between -1 and +1. +; Result in range 0 to pi. +; Derived from asn above which is in turn derived from the preceding atn. It +; could have been derived directly from atn using acs(x) = atn(sqr(1-x*x)/x). +; However, as sine and cosine are horizontal translations of each other, +; uses acs(x) = pi/2 - asn(x) + +; e.g. the arccosine of a known x value will give the required angle b in +; radians. +; We know, from above, how to calculate the angle a using asn(x). +; Since the three angles of any triangle add up to 180 degrees, or pi radians, +; and the largest angle in this case is a right-angle (pi/2 radians), then +; we can calculate angle b as pi/2 (both angles) minus asn(x) (angle a). +; +; +; /| +; 1 /b| +; / |x +; /a | +; /----| +; y + +;; acs +L1DD4: RST 28H ;; FP-CALC x. + DEFB $1F ;;asn asn(x). + DEFB $A3 ;;stk-pi/2 asn(x), pi/2. + DEFB $03 ;;subtract asn(x) - pi/2. + DEFB $18 ;;negate pi/2 - asn(x) = acs(x). + DEFB $34 ;;end-calc acs(x) + + RET ; return. + + +; -------------------------- +; THE 'SQUARE ROOT' FUNCTION +; -------------------------- +; (Offset $25: 'sqr') +; Error A if argument is negative. +; This routine is remarkable for its brevity - 7 bytes. +; The ZX81 code was originally 9K and various techniques had to be +; used to shoe-horn it into an 8K Rom chip. + + +;; sqr +L1DDB: RST 28H ;; FP-CALC x. + DEFB $2D ;;duplicate x, x. + DEFB $2C ;;not x, 1/0 + DEFB $00 ;;jump-true x, (1/0). + DEFB $1E ;;to L1DFD, LAST exit if argument zero + ;; with zero result. + +; else continue to calculate as x ** .5 + + DEFB $A2 ;;stk-half x, .5. + DEFB $34 ;;end-calc x, .5. + + +; ------------------------------ +; THE 'EXPONENTIATION' OPERATION +; ------------------------------ +; (Offset $06: 'to-power') +; This raises the first number X to the power of the second number Y. +; As with the ZX80, +; 0 ** 0 = 1 +; 0 ** +n = 0 +; 0 ** -n = arithmetic overflow. + +;; to-power +L1DE2: RST 28H ;; FP-CALC X,Y. + DEFB $01 ;;exchange Y,X. + DEFB $2D ;;duplicate Y,X,X. + DEFB $2C ;;not Y,X,(1/0). + DEFB $00 ;;jump-true + DEFB $07 ;;forward to L1DEE, XISO if X is zero. + +; else X is non-zero. function 'ln' will catch a negative value of X. + + DEFB $22 ;;ln Y, LN X. + DEFB $04 ;;multiply Y * LN X + DEFB $34 ;;end-calc + + JP L1C5B ; jump back to EXP routine. -> + +; --- + +; These routines form the three simple results when the number is zero. +; begin by deleting the known zero to leave Y the power factor. + +;; XISO +L1DEE: DEFB $02 ;;delete Y. + DEFB $2D ;;duplicate Y, Y. + DEFB $2C ;;not Y, (1/0). + DEFB $00 ;;jump-true + DEFB $09 ;;forward to L1DFB, ONE if Y is zero. + +; the power factor is not zero. If negative then an error exists. + + DEFB $A0 ;;stk-zero Y, 0. + DEFB $01 ;;exchange 0, Y. + DEFB $33 ;;greater-0 0, (1/0). + DEFB $00 ;;jump-true 0 + DEFB $06 ;;to L1DFD, LAST if Y was any positive + ;; number. + +; else force division by zero thereby raising an Arithmetic overflow error. +; There are some one and two-byte alternatives but perhaps the most formal +; might have been to use end-calc; rst 08; defb 05. + + DEFB $A1 ;;stk-one 0, 1. + DEFB $01 ;;exchange 1, 0. + DEFB $05 ;;division 1/0 >> error + +; --- + +;; ONE +L1DFB: DEFB $02 ;;delete . + DEFB $A1 ;;stk-one 1. + +;; LAST +L1DFD: DEFB $34 ;;end-calc last value 1 or 0. + + RET ; return. + +; --------------------- +; THE 'SPARE LOCATIONS' +; --------------------- + +;; SPARE +L1DFF: DEFB $FF ; That's all folks. + + + +; ------------------------ +; THE 'ZX81 CHARACTER SET' +; ------------------------ + +;; char-set - begins with space character. + +; $00 - Character: ' ' CHR$(0) + +L1E00: DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + +; $01 - Character: mosaic CHR$(1) + + DEFB %11110000 + DEFB %11110000 + DEFB %11110000 + DEFB %11110000 + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + + +; $02 - Character: mosaic CHR$(2) + + DEFB %00001111 + DEFB %00001111 + DEFB %00001111 + DEFB %00001111 + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + + +; $03 - Character: mosaic CHR$(3) + + DEFB %11111111 + DEFB %11111111 + DEFB %11111111 + DEFB %11111111 + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + +; $04 - Character: mosaic CHR$(4) + + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %11110000 + DEFB %11110000 + DEFB %11110000 + DEFB %11110000 + +; $05 - Character: mosaic CHR$(1) + + DEFB %11110000 + DEFB %11110000 + DEFB %11110000 + DEFB %11110000 + DEFB %11110000 + DEFB %11110000 + DEFB %11110000 + DEFB %11110000 + +; $06 - Character: mosaic CHR$(1) + + DEFB %00001111 + DEFB %00001111 + DEFB %00001111 + DEFB %00001111 + DEFB %11110000 + DEFB %11110000 + DEFB %11110000 + DEFB %11110000 + +; $07 - Character: mosaic CHR$(1) + + DEFB %11111111 + DEFB %11111111 + DEFB %11111111 + DEFB %11111111 + DEFB %11110000 + DEFB %11110000 + DEFB %11110000 + DEFB %11110000 + +; $08 - Character: mosaic CHR$(1) + + DEFB %10101010 + DEFB %01010101 + DEFB %10101010 + DEFB %01010101 + DEFB %10101010 + DEFB %01010101 + DEFB %10101010 + DEFB %01010101 + +; $09 - Character: mosaic CHR$(1) + + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %10101010 + DEFB %01010101 + DEFB %10101010 + DEFB %01010101 + +; $0A - Character: mosaic CHR$(10) + + DEFB %10101010 + DEFB %01010101 + DEFB %10101010 + DEFB %01010101 + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + +; $0B - Character: '"' CHR$(11) + + DEFB %00000000 + DEFB %00100100 + DEFB %00100100 + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + +; $0B - Character: £ CHR$(12) + + DEFB %00000000 + DEFB %00011100 + DEFB %00100010 + DEFB %01111000 + DEFB %00100000 + DEFB %00100000 + DEFB %01111110 + DEFB %00000000 + +; $0B - Character: '$' CHR$(13) + + DEFB %00000000 + DEFB %00001000 + DEFB %00111110 + DEFB %00101000 + DEFB %00111110 + DEFB %00001010 + DEFB %00111110 + DEFB %00001000 + +; $0B - Character: ':' CHR$(14) + + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %00010000 + DEFB %00000000 + DEFB %00000000 + DEFB %00010000 + DEFB %00000000 + +; $0B - Character: '?' CHR$(15) + + DEFB %00000000 + DEFB %00111100 + DEFB %01000010 + DEFB %00000100 + DEFB %00001000 + DEFB %00000000 + DEFB %00001000 + DEFB %00000000 + +; $10 - Character: '(' CHR$(16) + + DEFB %00000000 + DEFB %00000100 + DEFB %00001000 + DEFB %00001000 + DEFB %00001000 + DEFB %00001000 + DEFB %00000100 + DEFB %00000000 + +; $11 - Character: ')' CHR$(17) + + DEFB %00000000 + DEFB %00100000 + DEFB %00010000 + DEFB %00010000 + DEFB %00010000 + DEFB %00010000 + DEFB %00100000 + DEFB %00000000 + +; $12 - Character: '>' CHR$(18) + + DEFB %00000000 + DEFB %00000000 + DEFB %00010000 + DEFB %00001000 + DEFB %00000100 + DEFB %00001000 + DEFB %00010000 + DEFB %00000000 + +; $13 - Character: '<' CHR$(19) + + DEFB %00000000 + DEFB %00000000 + DEFB %00000100 + DEFB %00001000 + DEFB %00010000 + DEFB %00001000 + DEFB %00000100 + DEFB %00000000 + +; $14 - Character: '=' CHR$(20) + + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %00111110 + DEFB %00000000 + DEFB %00111110 + DEFB %00000000 + DEFB %00000000 + +; $15 - Character: '+' CHR$(21) + + DEFB %00000000 + DEFB %00000000 + DEFB %00001000 + DEFB %00001000 + DEFB %00111110 + DEFB %00001000 + DEFB %00001000 + DEFB %00000000 + +; $16 - Character: '-' CHR$(22) + + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %00111110 + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + +; $17 - Character: '*' CHR$(23) + + DEFB %00000000 + DEFB %00000000 + DEFB %00010100 + DEFB %00001000 + DEFB %00111110 + DEFB %00001000 + DEFB %00010100 + DEFB %00000000 + +; $18 - Character: '/' CHR$(24) + + DEFB %00000000 + DEFB %00000000 + DEFB %00000010 + DEFB %00000100 + DEFB %00001000 + DEFB %00010000 + DEFB %00100000 + DEFB %00000000 + +; $19 - Character: ';' CHR$(25) + + DEFB %00000000 + DEFB %00000000 + DEFB %00010000 + DEFB %00000000 + DEFB %00000000 + DEFB %00010000 + DEFB %00010000 + DEFB %00100000 + +; $1A - Character: ',' CHR$(26) + + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %00001000 + DEFB %00001000 + DEFB %00010000 + +; $1B - Character: '"' CHR$(27) + + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %00000000 + DEFB %00011000 + DEFB %00011000 + DEFB %00000000 + +; $1C - Character: '0' CHR$(28) + + DEFB %00000000 + DEFB %00111100 + DEFB %01000110 + DEFB %01001010 + DEFB %01010010 + DEFB %01100010 + DEFB %00111100 + DEFB %00000000 + +; $1D - Character: '1' CHR$(29) + + DEFB %00000000 + DEFB %00011000 + DEFB %00101000 + DEFB %00001000 + DEFB %00001000 + DEFB %00001000 + DEFB %00111110 + DEFB %00000000 + +; $1E - Character: '2' CHR$(30) + + DEFB %00000000 + DEFB %00111100 + DEFB %01000010 + DEFB %00000010 + DEFB %00111100 + DEFB %01000000 + DEFB %01111110 + DEFB %00000000 + +; $1F - Character: '3' CHR$(31) + + DEFB %00000000 + DEFB %00111100 + DEFB %01000010 + DEFB %00001100 + DEFB %00000010 + DEFB %01000010 + DEFB %00111100 + DEFB %00000000 + +; $20 - Character: '4' CHR$(32) + + DEFB %00000000 + DEFB %00001000 + DEFB %00011000 + DEFB %00101000 + DEFB %01001000 + DEFB %01111110 + DEFB %00001000 + DEFB %00000000 + +; $21 - Character: '5' CHR$(33) + + DEFB %00000000 + DEFB %01111110 + DEFB %01000000 + DEFB %01111100 + DEFB %00000010 + DEFB %01000010 + DEFB %00111100 + DEFB %00000000 + +; $22 - Character: '6' CHR$(34) + + DEFB %00000000 + DEFB %00111100 + DEFB %01000000 + DEFB %01111100 + DEFB %01000010 + DEFB %01000010 + DEFB %00111100 + DEFB %00000000 + +; $23 - Character: '7' CHR$(35) + + DEFB %00000000 + DEFB %01111110 + DEFB %00000010 + DEFB %00000100 + DEFB %00001000 + DEFB %00010000 + DEFB %00010000 + DEFB %00000000 + +; $24 - Character: '8' CHR$(36) + + DEFB %00000000 + DEFB %00111100 + DEFB %01000010 + DEFB %00111100 + DEFB %01000010 + DEFB %01000010 + DEFB %00111100 + DEFB %00000000 + +; $25 - Character: '9' CHR$(37) + + DEFB %00000000 + DEFB %00111100 + DEFB %01000010 + DEFB %01000010 + DEFB %00111110 + DEFB %00000010 + DEFB %00111100 + DEFB %00000000 + +; $26 - Character: 'A' CHR$(38) + + DEFB %00000000 + DEFB %00111100 + DEFB %01000010 + DEFB %01000010 + DEFB %01111110 + DEFB %01000010 + DEFB %01000010 + DEFB %00000000 + +; $27 - Character: 'B' CHR$(39) + + DEFB %00000000 + DEFB %01111100 + DEFB %01000010 + DEFB %01111100 + DEFB %01000010 + DEFB %01000010 + DEFB %01111100 + DEFB %00000000 + +; $28 - Character: 'C' CHR$(40) + + DEFB %00000000 + DEFB %00111100 + DEFB %01000010 + DEFB %01000000 + DEFB %01000000 + DEFB %01000010 + DEFB %00111100 + DEFB %00000000 + +; $29 - Character: 'D' CHR$(41) + + DEFB %00000000 + DEFB %01111000 + DEFB %01000100 + DEFB %01000010 + DEFB %01000010 + DEFB %01000100 + DEFB %01111000 + DEFB %00000000 + +; $2A - Character: 'E' CHR$(42) + + DEFB %00000000 + DEFB %01111110 + DEFB %01000000 + DEFB %01111100 + DEFB %01000000 + DEFB %01000000 + DEFB %01111110 + DEFB %00000000 + +; $2B - Character: 'F' CHR$(43) + + DEFB %00000000 + DEFB %01111110 + DEFB %01000000 + DEFB %01111100 + DEFB %01000000 + DEFB %01000000 + DEFB %01000000 + DEFB %00000000 + +; $2C - Character: 'G' CHR$(44) + + DEFB %00000000 + DEFB %00111100 + DEFB %01000010 + DEFB %01000000 + DEFB %01001110 + DEFB %01000010 + DEFB %00111100 + DEFB %00000000 + +; $2D - Character: 'H' CHR$(45) + + DEFB %00000000 + DEFB %01000010 + DEFB %01000010 + DEFB %01111110 + DEFB %01000010 + DEFB %01000010 + DEFB %01000010 + DEFB %00000000 + +; $2E - Character: 'I' CHR$(46) + + DEFB %00000000 + DEFB %00111110 + DEFB %00001000 + DEFB %00001000 + DEFB %00001000 + DEFB %00001000 + DEFB %00111110 + DEFB %00000000 + +; $2F - Character: 'J' CHR$(47) + + DEFB %00000000 + DEFB %00000010 + DEFB %00000010 + DEFB %00000010 + DEFB %01000010 + DEFB %01000010 + DEFB %00111100 + DEFB %00000000 + +; $30 - Character: 'K' CHR$(48) + + DEFB %00000000 + DEFB %01000100 + DEFB %01001000 + DEFB %01110000 + DEFB %01001000 + DEFB %01000100 + DEFB %01000010 + DEFB %00000000 + +; $31 - Character: 'L' CHR$(49) + + DEFB %00000000 + DEFB %01000000 + DEFB %01000000 + DEFB %01000000 + DEFB %01000000 + DEFB %01000000 + DEFB %01111110 + DEFB %00000000 + +; $32 - Character: 'M' CHR$(50) + + DEFB %00000000 + DEFB %01000010 + DEFB %01100110 + DEFB %01011010 + DEFB %01000010 + DEFB %01000010 + DEFB %01000010 + DEFB %00000000 + +; $33 - Character: 'N' CHR$(51) + + DEFB %00000000 + DEFB %01000010 + DEFB %01100010 + DEFB %01010010 + DEFB %01001010 + DEFB %01000110 + DEFB %01000010 + DEFB %00000000 + +; $34 - Character: 'O' CHR$(52) + + DEFB %00000000 + DEFB %00111100 + DEFB %01000010 + DEFB %01000010 + DEFB %01000010 + DEFB %01000010 + DEFB %00111100 + DEFB %00000000 + +; $35 - Character: 'P' CHR$(53) + + DEFB %00000000 + DEFB %01111100 + DEFB %01000010 + DEFB %01000010 + DEFB %01111100 + DEFB %01000000 + DEFB %01000000 + DEFB %00000000 + +; $36 - Character: 'Q' CHR$(54) + + DEFB %00000000 + DEFB %00111100 + DEFB %01000010 + DEFB %01000010 + DEFB %01010010 + DEFB %01001010 + DEFB %00111100 + DEFB %00000000 + +; $37 - Character: 'R' CHR$(55) + + DEFB %00000000 + DEFB %01111100 + DEFB %01000010 + DEFB %01000010 + DEFB %01111100 + DEFB %01000100 + DEFB %01000010 + DEFB %00000000 + +; $38 - Character: 'S' CHR$(56) + + DEFB %00000000 + DEFB %00111100 + DEFB %01000000 + DEFB %00111100 + DEFB %00000010 + DEFB %01000010 + DEFB %00111100 + DEFB %00000000 + +; $39 - Character: 'T' CHR$(57) + + DEFB %00000000 + DEFB %11111110 + DEFB %00010000 + DEFB %00010000 + DEFB %00010000 + DEFB %00010000 + DEFB %00010000 + DEFB %00000000 + +; $3A - Character: 'U' CHR$(58) + + DEFB %00000000 + DEFB %01000010 + DEFB %01000010 + DEFB %01000010 + DEFB %01000010 + DEFB %01000010 + DEFB %00111100 + DEFB %00000000 + +; $3B - Character: 'V' CHR$(59) + + DEFB %00000000 + DEFB %01000010 + DEFB %01000010 + DEFB %01000010 + DEFB %01000010 + DEFB %00100100 + DEFB %00011000 + DEFB %00000000 + +; $3C - Character: 'W' CHR$(60) + + DEFB %00000000 + DEFB %01000010 + DEFB %01000010 + DEFB %01000010 + DEFB %01000010 + DEFB %01011010 + DEFB %00100100 + DEFB %00000000 + +; $3D - Character: 'X' CHR$(61) + + DEFB %00000000 + DEFB %01000010 + DEFB %00100100 + DEFB %00011000 + DEFB %00011000 + DEFB %00100100 + DEFB %01000010 + DEFB %00000000 + +; $3E - Character: 'Y' CHR$(62) + + DEFB %00000000 + DEFB %10000010 + DEFB %01000100 + DEFB %00101000 + DEFB %00010000 + DEFB %00010000 + DEFB %00010000 + DEFB %00000000 + +; $3F - Character: 'Z' CHR$(63) + + DEFB %00000000 + DEFB %01111110 + DEFB %00000100 + DEFB %00001000 + DEFB %00010000 + DEFB %00100000 + DEFB %01111110 + DEFB %00000000 + +.END ;TASM assembler instruction. \ No newline at end of file