mirror of
https://github.com/nathanriggs/AppleIIAsm-Collection.git
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eb2b7deea0
- 16bit array subroutines will be added here at a later date. - Strings library separated from arrays on its own disk in anticipation of larger libraries.
146 lines
3.0 KiB
Plaintext
146 lines
3.0 KiB
Plaintext
*
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*``````````````````````````````*
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* AGET81 :: GET ARRAY ELEMENT *
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* ADDRESS *
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*- -*
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* GETS THE ADDRESS LOCATION OF *
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* AN ELEMENT IN THE SPECIFIED *
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* ARRAY AT THE SPECIFIED INDEX *
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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 ;HI ARADDR *
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* PHA *
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* LDA #<$300 ; LOW *
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* PHA *
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* LDA #5 ; INDEX *
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* PHA *
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* JSR AGET81 *
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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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* INDEX OF ELEMENT TO GET *
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* ADDRESS OF ARRAY LO BYTE *
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* ADDRESS OF ARRAY HI BYTE *
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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 = LOBYTE OF ELEMENT ADDR *
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* X = HIBYTE OF ELEMENT ADDR *
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* A = TRASH *
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*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
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*
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AGET81
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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 :IDX
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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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** GET ELEMENT SIZE
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*
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LDY #1 ; ELEMENT SIZE LOC
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LDA (ADDR1),Y
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STA :ESIZE
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*
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*
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** FIRST, MUL INDEX BY ELEMENT SIZE,
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** THEN ADD TWO TO GET THE PROPER ADDRESS.
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*
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LDY #0
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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 :IDX
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TAX
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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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:LP
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ASL :IDX
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ROL SCRATCH
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:ENTLP
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LSR :ESIZE
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BCS :DOADD
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BNE :LP
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*
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** ARRAY INDEX STORED IN X (LOW) AND Y (HIGH)
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*
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STX :IDX
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STY :IDX+1
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*
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** ADD 2 TO INDEX
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*
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CLC
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LDA #2
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ADC :IDX
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STA :RES
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LDA #0
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ADC :IDX+1
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STA :RES+1
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*
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** NOW ADD THAT TO BASE ARRAY ADDRESS
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** TO GET ADDRESS OF INDEX VALUE
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*
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CLC
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LDA :RES
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ADC ADDR1 ; LOW OF ARRAY ADDRESS
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STA :RES
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LDA :RES+1
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ADC ADDR1+1
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STA :RES+1
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*
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** ADDRESS TO ARRAY ELEMENT IS STORED
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** IN Y (LOW BYTE), X (HIGH BYTE)
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*
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LDY :RES
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LDX :RES+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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:RES DS 2
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:IDX DS 2
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:ESIZE DS 1
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*
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