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https://github.com/nathanriggs/AppleIIAsm-Collection.git
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101 lines
2.1 KiB
Plaintext
101 lines
2.1 KiB
Plaintext
*
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*``````````````````````````````*
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* MUL8 :: 8BIT MULTIPLY (16BR) *
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*- -*
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* MULTIPLY TWO 8BIT NUMBERS TO *
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* GET 16BIT RESULT. NUMBERS *
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* MUST BE UNSIGNED. *
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* *
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* ORIGINAL AUTHOR IS WHITE *
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* FLAME, AS SHARED ON *
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* CODEBASE64. I HAVE MADE SOME *
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* MINOR ALTERATIONS, BUT NOT *
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* NEARLY ENOUGH TO CALL IT MY *
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* OWN. *
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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 #100 *
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* PHA *
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* PDA #200 *
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* PHA *
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* JSR MUL8 *
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*- -*
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* ENTRY *
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* *
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* LOW BYTE OF RETURN ADDRESS *
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* HIGH BYTE OF RETURN ADDRESS *
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* SECOND NUM TO BE MULTIPLIED *
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* FIRST NUM TO BE MULTIPLIED *
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*- -*
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* EXIT *
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* *
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* Y = HIGH BYTE OF PRODUCT *
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* X = LOW BYTE OF PRODUCT *
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* A = LOW BYTE OF PRODUCT *
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*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
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*
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MUL8
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*
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** GET 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 :MUL1
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PLA
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STA :MUL2
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*
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** INIT
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*
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LDA #$00
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TAX
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STX :MUL1H
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BEQ :GOLOOP
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*
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:DOADD
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CLC
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ADC :MUL1
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TAY
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*
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TXA
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ADC :MUL1H
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TAX
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TYA
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*
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:LP
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ASL :MUL1
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ROL :MUL1H
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:GOLOOP
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LSR :MUL2
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BCS :DOADD
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BNE :LP
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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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:MUL1 DS 1
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:MUL2 DS 1
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:RETADR DS 2
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:MUL1H DS 1
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