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https://github.com/nathanriggs/AppleIIAsm-Collection.git
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90 lines
2.1 KiB
Plaintext
90 lines
2.1 KiB
Plaintext
*
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*``````````````````````````````*
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* RAND16 : 16BIT RANDOM NUMBER *
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*- -*
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* GENERATE A 16BIT PSEUDO- *
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* RANDOM NUMBER AND RETURN IT *
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* IN Y,X (LOW, HIGH). *
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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. *
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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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*- -*
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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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*- -*
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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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* [RETURN] = RESULT (2 BYTES) *
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* [RETLEN] = 2 (RESULT LENGTH) *
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*- -*
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* NOTE: THERE ARE 2048 MAGIC *
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* NUMBERS THAT COULD BE EOR'D *
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* TO GENERATE A PSEUDO-RANDOM *
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* PATTERN THAT DOESN'T REPEAT *
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* UNTIL 65535 ITERATIONS. TOO *
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* MANY TO LIST HERE, BUT SOME *
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* ARE: $002D, $1979, $1B47, *
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* $41BB, $3D91, $B5E9, $FFEB *
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*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
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*
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RAND16
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*
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LDA RNDL
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STA :SEED
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LDA RNDH
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STA :SEED+1
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*
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LDA :SEED
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BEQ :LOW0
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*
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** DO A NORMAL SHIFT
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*
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ASL :SEED
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LDA :SEED+1
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ROL
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BCC :NOEOR
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:DOEOR ; HIGH BYTE IN A
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EOR #>$0369
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STA :SEED+1
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LDA :SEED
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EOR #<$0369
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STA :SEED
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JMP :EXIT
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:LOW0
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LDA :SEED+1
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BEQ :DOEOR
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ASL
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BEQ :NOEOR
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BCS :DOEOR
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:NOEOR
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STA :SEED+1
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:EXIT LDX :SEED+1
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LDY :SEED
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STY RETURN
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STX RETURN+1
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LDA #2
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STA RETLEN
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RTS
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*
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** DATA
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*
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:SEED DS 2
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*
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