mirror of
https://github.com/nathanriggs/AppleIIAsm-Collection.git
synced 2024-11-30 15:49:55 +00:00
192 lines
3.8 KiB
Plaintext
192 lines
3.8 KiB
Plaintext
*
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*``````````````````````````````*
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* RANDB :: RANDOM BYTE *
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*- -*
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* RETURNS A RANDOM BYTE VALUE *
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* BETWEEN THE HIGH AND LOW *
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* BOUNDS PASSED TO ROUTINE. *
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* NOTE THAT THIS ONLY WORKS *
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* WITH UNSIGNED VALUES. *
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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 #1 ; LOW BOUND *
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* PHA *
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* LDA #100 ; HIGH *
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* PHA *
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* JSR RANDB *
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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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*- -*
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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 = COUNTER; TRASH *
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* .X = COUNTER; TRASH *
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* .A = LOW BYTE OF RET ADDR *
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*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
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*
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RANDB
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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 :NEWMAX
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PLA
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STA :NEWMIN
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*
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** GET OLDMIN,OLDMAX,OLDVAL
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*
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LDA #1
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STA :OLDMIN
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LDA #255
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STA :OLDMAX
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JSR RAND8 ; RANDOM BYTE 0..255
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STA :OLDVAL
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*
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** NEWVALUE = (((OLDVAL-NEWMIN) * (NEWMAX-NEWMIN) /
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** (OLDMAX-OLDMIN)) + NEWMIN
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*
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** OR
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*
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** OLDRANGE = (OLDMAX-OLDMIN)
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** NEWRANGE = (NEWMAX - NEWMIN)
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** NEWVAL = (((OLDVAL-OLDMIN) * NEWRANGE) / OLDRANGE) + NEWMIN
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*
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** GET OLDRANGE: OLDMAX - OLDMIN
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*
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LDA :OLDMAX
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SEC
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SBC :OLDMIN
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STA :OLDRANGE
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*
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** NOW GET NEWRANGE: NEWMAX - NEWMIN
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*
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LDA :NEWMAX
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SEC
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SBC :NEWMIN
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STA :NEWRANGE
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*
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** NOW GET VALRANGE: OLDVAL - OLDMIN
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*
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LDA :OLDVAL
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SEC
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SBC :OLDMIN
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STA :VALRANGE
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*
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** GET MULRANGE: VALRANGE * NEWRANGE
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*
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LDA #00
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TAY
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STY :NUM1HI
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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 :VALRANGE
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TAX
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*
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TYA
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ADC :NUM1HI
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TAY
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TXA
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*
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:MLP
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ASL :VALRANGE
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ROL :NUM1HI
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:ENTLP
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LSR :NEWRANGE
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BCS :DOADD
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BNE :MLP
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*
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STA :MULRANGE
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STY :MULRANGE+1
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*
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** NOW GET DIVRANGE: MULRANGE / OLDRANGE
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*
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:DIVIDE
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LDA #0
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STA :REMAIN
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STA :REMAIN+1
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LDX #16
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*
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:DIVLP
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ASL :MULRANGE
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ROL :MULRANGE+1
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ROL :REMAIN
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ROL :REMAIN+1
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LDA :REMAIN
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SEC
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SBC :OLDRANGE
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TAY
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LDA :REMAIN+1
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SBC :OLDRANGE+1
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BCC :SKIP
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*
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STA :REMAIN+1
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STY :REMAIN
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INC :DIVRANGE
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*
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:SKIP DEX
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BNE :DIVLP
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*
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** NOW ADD NEWMIN TO DIVRANGE
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*
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LDA :DIVRANGE ; LO BYTE ONLY
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CLC
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ADC :NEWMIN
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STA :NEWVAL
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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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LDA :NEWVAL ; RETURN # IN A
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STA RETURN
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LDX #1
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STX RETLEN
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RTS
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*
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** DATA
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*
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:OLDRANGE DS 2
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:NEWRANGE DS 2
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:MULRANGE DS 2
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:DIVRANGE DS 2
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:VALRANGE DS 2
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:OLDVAL DS 2
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:NEWVAL DS 2
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:OLDMIN DS 2
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:NEWMIN DS 2
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:OLDMAX DS 2
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:NEWMAX DS 2
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:NUM1HI DS 2
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:REMAIN DS 2
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*
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