mirror of
https://github.com/nathanriggs/AppleIIAsm-Collection.git
synced 2024-06-08 01:29:28 +00:00
99 lines
3.7 KiB
NASM
99 lines
3.7 KiB
NASM
*
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*``````````````````````````````*
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* AGET161 (NATHAN RIGGS) *
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* *
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* GET DATA IN 16-BIT, 2D ARRAY *
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* *
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*------------------------------*
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* MULTIPLICATION CODE ADAPTED *
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* FROM WHITE FLAME'S WORK ON *
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* CODEBASE64. LICENSE MAY VARY *
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*------------------------------*
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* *
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* INPUT: *
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* *
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* ZPW1 = ARRAY ADDRESS *
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* ZPW2 = ELEMENT INDEX *
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* *
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* DESTROY: NZCIDV *
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* ^^^ ^ *
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* *
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* CYCLES: 185+ *
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* SIZE: 113 BYTES *
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*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
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*
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]AIDX EQU ZPW2 ; ELEMENT INDEX
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]ADDR EQU ZPW1 ; ARRAY ADDRESS
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*
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]ESIZE EQU ZPB1 ; ELEMENT LENGTH
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]ESIZEB EQU ZPB2 ; ^BACKUP
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]ASIZE EQU ZPW3 ; NUMBER OF ELEMENTS
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]IDX EQU ZPW4 ; INDEX BACKUP
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*
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AGET161
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LDA ]AIDX ; {3C2B}
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STA ]IDX ; {3C2B}
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LDA ]AIDX+1 ; {3C2B} GET INDEX HIBYTE
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STA ]AIDX+1 ; {3C2B}
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STA ZPB3 ; {3C2B}
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LDY #0 ; {2C2B} RESET INDEX
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LDA (]ADDR),Y ; {6C2B} GET NUMBER OF
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STA ]ASIZE ; {3C2B} ARRAY ELEMENTS
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LDY #1 ; {2C2B} GET HIBYTE OF
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LDA (]ADDR),Y ; {6C2B} # OF ARRAY ELEMENTS
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STA ]ASIZE+1 ; {3C2B}
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INY ; {2C1B} INCREASE BYTE INDEX
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LDA (]ADDR),Y ; {6C2B} GET ELEMENT LENGTH
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STA ]ESIZE ; {3C2B}
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STA ]ESIZEB ; {3C2B}
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*
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** MULTIPLY INDEX BY ELEMENT SIZE, ADD 3
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*
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LDY #0 ; {2C2B} RESET .Y AND .A
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LDA #0 ; {2C2B}
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BEQ :ENTLPA ; {3C2B} IF ZERO, SKIP TO LOOP
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:DOADD
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CLC ; {2C1B} CLEAR CARRY
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ADC ]AIDX ; {4C3B} ADD INDEX TO .A
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TAX ; {2C1B} HOLD IN .X
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TYA ; {2C1B} LOAD HIBYTE
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ADC ZPB3 ; {4C3B} ADD HIBYTE
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TAY ; {2C1B} HOLD IN .Y
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TXA ; {2C1B} RELOAD LOBYTE
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:LPA
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ASL ]AIDX ; {6C3B} MULTIPLY INDEX BY 2
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ROL ZPB3 ; {6C3B} ADJUST HIBYTE
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:ENTLPA
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LSR ]ESIZE ; {6C3B} DIVIDE ELEMENT LENGTH BY 2
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BCS :DOADD ; {3C2B} IF BIT1 SHIFTED IN CARRY +MORE
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BNE :LPA ; {3C2B} CONTINUE LOOPING IF Z FLAG UNSET
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STX ]IDX ; {3C2B} STORE LOBYTE
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STY ]IDX+1 ; {3C2B} STORE HIBYTE
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LDA #3 ; {2C2B} ADD 3 TO INDEX LOBYTE
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CLC ; {2C1B} CLEAR CARRY
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ADC ]IDX ; {4C3B}
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STA ZPW5 ; {3C2B} STORE ON ZERO PAGE
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LDA ]IDX+1 ; {3C2B} ADJUST HIBYTE
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ADC #0 ; {2C2B}
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STA ZPW5+1 ; {3C2B}
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*
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LDA ZPW5 ; {3C2B} ADD ARRAY ADDRESS
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CLC ; {2C1B}
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ADC ]ADDR ; {4C3B} LOBYTE
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STA ZPW5 ; {3C2B}
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LDA ZPW5+1 ; {3C2B} HIBYTE
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ADC ]ADDR+1 ; {4C3B}
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STA ZPW5+1 ; {3C2B}
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LDY #0 ; {2C2B} RESET BYTE INDEX
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:LP
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LDA (ZPW5),Y ; {6C2B} GET BYTE FROM ELEMENT
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STA RETURN,Y ; {3C2B} PUT INTO RETURN
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INY ; {2C1B} INCREASE BYTE INDEX
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CPY ]ESIZEB ; {4C3B} IF INDEX != ELEMENT LENGTH
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BNE :LP ; {3C2B} CONTINUE LOOP
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LDA ]ESIZEB ; {3C2B} .A = ELEMENT SIZE
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STA RETLEN ; {3C2B} STORE IN RETLEN
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LDY ZPW5+1 ; {3C2B} .Y = ELEMENT ADDRESS HIBYTE
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LDX ZPW5 ; {3C2B} .X = ELEMENT ADDRESS LOBYTE
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RTS ; {6C1B}
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