mirror of
https://github.com/nathanriggs/AppleIIAsm-Collection.git
synced 2024-12-11 09:49:17 +00:00
176 lines
3.6 KiB
Plaintext
176 lines
3.6 KiB
Plaintext
*
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*``````````````````````````````*
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* AGET82 : INIT 2D ARRAY *
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*- -*
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* THIS GETS THE ADDRESS OF AN *
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* ELEMENT AT THE INDEX OF *
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* [:XIDX],[:YIDX]. *
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*- -*
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* CLOBBERS: *
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* *
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* FLAGS: ????---- REG: AXYM *
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*- -*
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* CYCLES: ??? *
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* SIZE: *
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*- -*
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* USAGE: *
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* *
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* LDA #>$300 ; ARRAY ADDR *
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* PHA *
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* LDA #<$300 *
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* PHA *
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* LDA #2 ; X INDEX *
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* PHA *
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* LDA #3 ; Y INDEX *
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* PHA *
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* JSR AGET82 *
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*- -*
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* ENTRY *
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* *
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* TOP OF STACK *
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* *
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* LOW BYTE OF RETURN ADDRESS *
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* HI BYTE OF RETURN ADDRESS *
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* Y INDEX OF ELEMENT *
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* X INDEX OF ELEMENT *
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* LOW BYTE OF ARRAY ADDRESS *
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* HIGH BYTE OF ARRAY ADDRESS *
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*- -*
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* EXIT *
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* *
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* TOP OF STACK *
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* *
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* LOW BYTE OF RETURN ADDRESS *
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* HI BYTE OF RETURN ADDRESS *
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* *
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* .Y = LO BYTE OF ELEM ADDR *
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* .X = HI BYTE OF ELEM ADDR *
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* .A = ELEMENT/RETURN LENGTH *
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* *
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* [RETURN] = VALUE FOUND AT *
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* SPECIFIED INDEX. *
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* *
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* [RETLEN] = LENGTH IN BYTES *
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* OF THE RETURN VALUE. *
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*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
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*
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AGET82
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*
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** SAVE RETURN ADDRESS
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*
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PLA
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STA RETADR
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PLA
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STA RETADR+1
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*
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** GET PARAMETERS
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*
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PLA
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STA :YIDX
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PLA
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STA :XIDX
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PLA
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STA ADDR1
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PLA
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STA ADDR1+1
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*
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LDY #2
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LDA (ADDR1),Y ; ELEMENT LENGTH
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STA :MCAND ; ELEMENT LENGTH
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LDA #0
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STA :MCAND+1
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*
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** MULTIPLY X AND Y
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*
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LDA #0
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TAY
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STY SCRATCH
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BEQ :ENTLP
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*
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:DOADD
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CLC
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ADC :XIDX
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TAX
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*
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TYA
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ADC SCRATCH
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TAY
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TXA
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*
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:LP
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ASL :XIDX
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ROL SCRATCH
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:ENTLP
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LSR :YIDX
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BCS :DOADD
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BNE :LP
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*
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STX :MLIER
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STY :MLIER+1
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*
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** NOW MULTIPLY BY LENGTH OF ELEMENTS
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*
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LDA #0
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STA :PROD+2
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STA :PROD+3
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LDX #$10
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:SHIFTR LSR :MLIER+1
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ROR :MLIER
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BCC :ROTR
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LDA :PROD+2
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CLC
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ADC :MCAND
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STA :PROD+2
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LDA :PROD+3
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ADC :MCAND+1
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:ROTR
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ROR
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STA :PROD+3
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ROR :PROD+2
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ROR :PROD+1
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ROR :PROD
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DEX
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BNE :SHIFTR
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*
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CLC
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INC :PROD ; INCREASE BY 3
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INC :PROD
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INC :PROD
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BCC :NOCAR
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INC :PROD+1
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:NOCAR
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*
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** NOW ADD BASE ADDRESS OF ARRAY TO GET
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** THE ADDRESS OF THE INDEX VALUE
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*
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CLC
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LDA :PROD
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ADC ADDR1
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STA :PROD
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LDA :PROD+1
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ADC ADDR1+1
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STA :PROD+1
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*
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** RETURN ADDRESS IN Y(LOW) AND X(HIGH)
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*
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LDY :PROD
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LDX :PROD+1
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*
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** RESTORE RETURN ADDRESS
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*
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LDA RETADR+1
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PHA
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LDA RETADR
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PHA
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*
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RTS
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*
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** DATA
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*
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:XIDX DS 2
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:YIDX DS 2
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:PROD DS 4
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:MLIER DS 2
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:MCAND DS 2
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*
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