mirror of
https://github.com/nathanriggs/AppleIIAsm-Collection.git
synced 2024-12-01 06:49:59 +00:00
152 lines
3.6 KiB
Plaintext
152 lines
3.6 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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*- -*
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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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* *** NOTE: I DON'T LIKE THAT *
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* THIS HAS TO CALL UDIV16, AND *
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* THUS CANNOT BE INCLUDED ON *
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* ITS OWN. IN FUTURE, HANDLE *
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* DIVISION WITHIN ROUTINE, *
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* ESPECIALLY SINCE IT IS 8BIT. *
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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 :RHB ; HIGH BOUND
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PLA
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STA :RLB ; LOW BOUND
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*
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** FORMULA: F = L + (R-((R\(H-L))*(H-L)
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*
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LDA :RHB
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CLC
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ADC #2 ; NO IDEA WHY I NEED
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; THIS BUT I DO
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STA :RHB
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LDA :RHB ;LOAD IN HIGH RANGE
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SEC
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SBC :RLB ;SUBTRACT LOW RANGE
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STA :RHL ;STORE HIGH - LOW HERE
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JSR RND8 ; GET NUM BETWEEN 0..255
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STA :R ; RANDOM 0,,255
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*
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** R\(H-L)
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*
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LDX #0 ; STORE 0 FOR HIGH BYTE
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STX :R+1 ; 0 HIGH BYTE
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STX :RHL+1 ; 0 HIGH BYTE
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LDA :R+1
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PHA
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LDA :R
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PHA
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LDA :RHL+1 ; LOAD (H-L) BACK INTO A
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PHA
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LDA :RHL
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PHA
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JSR UDIV16 ; DIV (H-L) BY __R
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PLA
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STA :QUOT
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PLA
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STA :QUOT+1
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*
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** R-(R\(H-L)
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*
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LDA :R ; LOAD RND BACK INTO A
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SEC
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SBC :QUOT ; SUBTRACT (R/(H-L) FROM RND8
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STA :QUOT ; STORE TEMP
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*
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** (R-(R\(H-L))*(H-L)
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*
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LDA #0 ; ZERO HIGH BYTE
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STA :QUOT+1 ; 0 HIGH BYTE
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LDA :RHL+1 ; LOAD (H-L)
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PHA
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LDA :RHL
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PHA
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LDA :QUOT+1
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PHA
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LDA :QUOT
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PHA
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JSR MUL16 ; MUL (H-L) * __R - (H-L)
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PLA
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STA :RESULT
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PLA
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STA :RESULT+1
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*
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** L + EVERYTHING ELSE
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*
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CLC
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ADC :RLB ;ADD LOW BYTE TO ALL ELSE
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:FINISH
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STA :RESULT ; STORE IN RESULT
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LDX :RESULT+1 ; HIGH BYTE; FOR
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; DEBUGGING PURPOSES
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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 :RESULT ; RETURN # IN A
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RTS
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*
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** DATA
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*
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:R DS 2
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:RETADR DS 2
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:RESULT DS 2
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:RHB DS 2
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:RLB DS 2
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:RHL DS 2
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:QUOT DS 2
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