mirror of
https://github.com/nathanriggs/AppleIIAsm-Collection.git
synced 2024-12-03 18:49:28 +00:00
125 lines
4.2 KiB
NASM
125 lines
4.2 KiB
NASM
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*``````````````````````````````*
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* INTASC2HEX (NATHAN RIGGS) *
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* *
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* INPUT: *
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* *
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* WPAR1 = STRING ADDRESS *
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* *
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* OUTPUT: *
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* *
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* .A = HEX VALUE LOW BYTE *
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* .X = HEX VALUE HIGH BYTE *
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* RETURN = HEX VALUE *
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* RETLEN = 2 *
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* *
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* DESTROYS: AXYNVBDIZCMS *
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* ^^^^ ^^^ *
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* *
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* CYCLES: 266+ *
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* SIZE: 196 BYTES *
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*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
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*
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]NACCUM EQU VARTAB
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]SIGN EQU VARTAB+4
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]NINDEX EQU VARTAB+6
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]STR EQU WPAR1
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*
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INTASC2HEX
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*
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LDY #0 ; INIT INDEX
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LDA (]STR),Y ; GET STRING LENGTH
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TAX ; TRANSFER TO .X
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LDA #1 ; SET NINDEX TO 1
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STA ]NINDEX ;
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LDA #0 ; INIT ]NACCUM LOW, HIGH
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STA ]NACCUM ; ACCUM = 0
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STA ]NACCUM+1
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STA ]SIGN ; INIT SIGN TO 0 (POSITIVE)
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TXA ; TRANSFER .X BACK TO .A
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BNE :INIT1 ; IF .A != 0, CONTINUE INIT
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JMP :EREXIT ; ELSE, EXIT WITH ERROR--NO STRING
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:INIT1
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LDY ]NINDEX ; INITIALLY, SET TO 1
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LDA (]STR),Y ; LOAD FIRST CHARACTER
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CMP #173 ; IF .A != "-"
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BNE :PLUS ; THEN NUMBER IS POSITIVE
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LDA #$0FF ; ELSE SET FLAG TO NEGATIVE
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STA ]SIGN
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INC ]NINDEX ; INCREASE INDEX
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DEX ; DECREMENT LENGTH COUNT
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BEQ :EREXIT ; EXIT WITH ERROR IF .X = 0
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JMP :CNVERT
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:PLUS
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CMP #'+'
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BNE :CHKDIG ; START CONVERSION IF 1ST
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; CHARACTER IS NOT A +
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INC ]NINDEX ; INCREASE NEW INDEX
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DEX ; DEC COUNT; IGNORE + SIGN
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BEQ :EREXIT ; ERROR EXIT IF ONLY
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; + IN THE BUFFER
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:CNVERT
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LDY ]NINDEX ; GET NEW INDEX
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LDA (]STR),Y ; GET NEXT CHARACTER
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:CHKDIG ; CHECK DIGIT
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CMP #$B0 ; "0"
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BMI :EREXIT ; ERROR IF NOT A NUMERAL
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CMP #$BA ; '9'+1; TECHNICALLY :
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BPL :EREXIT ; ERR IF > 9 (NOT NUMERAL)
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PHA ; PUSH DIGIT TO STACK
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*
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** VALID DECIMAL DIGIT SO
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** ACCUM = ACCUM * 10
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** = ACCUM * (8+2)
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** = (ACCUM * 8) + (ACCUM * 2)
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*
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ASL ]NACCUM
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ROL ]NACCUM+1 ; TIMES 2
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LDA ]NACCUM
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LDY ]NACCUM+1 ; SAVE ACCUM * 2
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ASL ]NACCUM
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ROL ]NACCUM+1
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ASL ]NACCUM
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ROL ]NACCUM+1 ; TIMES 8
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CLC
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ADC ]NACCUM ; SUM WITH * 2
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STA ]NACCUM
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TYA
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ADC ]NACCUM+1
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STA ]NACCUM+1 ; ACCUM=ACCUM * 10
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*
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PLA ; GET THE DIGIT FROM STACK
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SEC ; SET CARRY
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SBC #$B0 ; SUBTRACT ASCII '0'
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CLC ; CLEAR CARRY
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ADC ]NACCUM ; ADD TO ACCUMULATION
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STA ]NACCUM ; STORE IN ACCUMULATION
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LDA #0 ; NOW ADJUST HIGH BYTE
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ADC ]NACCUM+1
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STA ]NACCUM+1
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INC ]NINDEX ;INC TO NEXT CHARACTER
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DEX ; DECREMENT .X COUNTER
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BNE :CNVERT ; IF .X != 0, CONTINUE CONVERSION
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LDA ]SIGN ; ELSE LOAD SIGN FLAG
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BPL :OKEXIT ; IF POSITIVE, EXIT WITHOUT ERROR
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LDA #0 ; ELSE SET THE VALUE TO NEGATIVE
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SEC ; SET CARRY
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SBC ]NACCUM ; 0 - ]NACCUM
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STA ]NACCUM ; STORE AS ]NACCUM
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LDA #0 ; ADJUST HIGHBYTE
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SBC ]NACCUM+1
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STA ]NACCUM+1
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*
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:OKEXIT
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CLC ; CLEAR CARRY TO SIGNIFY NO ERRORS
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BCC :EXIT
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:EREXIT
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SEC ; SET CARRY TO INIDICATE ERROR
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:EXIT
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LDA #2 ; BYTE LENGTH IS 2
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STA RETLEN
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LDX ]NACCUM+1 ; LOAD HIGH BYTE INTO .X
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LDA ]NACCUM ; AND LOW BYTE INTO .A
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STA RETURN ; ALSO STORE RESULT IN RETURN
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STX RETURN+1
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RTS
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