mirror of
https://github.com/nathanriggs/AppleIIAsm-Collection.git
synced 2024-11-30 15:49:55 +00:00
100 lines
2.7 KiB
Plaintext
100 lines
2.7 KiB
Plaintext
SUBCOPY
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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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PLA
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STA :MLEN
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PLA
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STA :SCNT
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STA RETLEN
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PLA
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STA :SINDEX
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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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LDA #<RETURN
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STA ADDR2
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LDA #>RETURN
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STA ADDR2+1
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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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LDA #0
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STA :S2LEN ; DESTINATION LENGTH = 0
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STA :SCERR ; ASSUME NO ERRORS
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LDA :SCNT
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BEQ :OKEXIT ; BR IF 0 BYTES TO COPY,
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LDA :MLEN
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BEQ :EREXIT ; ERROR EXIT IF SUBSTR HAS
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LDA :SINDEX
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BEQ :EREXIT ; ERROR EXIT IF START IDX = 0
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LDY #0
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LDA (ADDR1),Y ;
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STA :S1LEN ; GET LENGTH OF SOURCE STRING
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CMP :SINDEX ; COMPARE TO STARTING INDEX
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BCC :EREXIT ; ERROR EXIT IF INDEX TOO BIG
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LDA :SINDEX
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CLC
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ADC :SCNT
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BCS :RECALC
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TAX ; BR IF INDEX + COUNT > 255
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DEX
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CPX :S1LEN
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BCC :CNT10K ; BR IF IND + CNT - 1 < S1LEN
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BEQ :CNT10K ; OR EQUAL
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:RECALC
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LDA :S1LEN ; RECALCULATE COUNT
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SEC
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SBC :SINDEX
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STA :SCNT
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INC :SCNT ; CNT = S1LEN - IND + 1
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LDA #$0FF
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STA :SCERR ; INDICATE TRUNCATION
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:CNT10K
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LDA :SCNT
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CMP :MLEN ; IF CNT > M SUBSTR LEN ?
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BCC :CNT20K ; BR IF CNT < MAXLEN
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BEQ :CNT20K ; BR IF CNT = MAXLEN
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LDA :MLEN
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STA :SCNT ; ELSE CNT = MAXLEN
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LDA #$0FF
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STA :SCERR ; INDICATE DEST STR OVERFLOW
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:CNT20K
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LDX :SCNT ; REG X WILL BE COUNTER
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BEQ :EREXIT ; ERR IF 0
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LDA #1 ; START WITH 1ST CHAR IN DEST
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STA :S2LEN ; RUNNING DEST INDEX
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; __SINDEX IS SRC INDEX
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:MVLP
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LDY :SINDEX
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LDA (ADDR1),Y ; GET NEXT SRC CHAR
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LDY :S2LEN
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STA (ADDR2),Y ; MOVE NEXT CHAR TO DEST
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INC :SINDEX ; INC SRC INDEX
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INC :S2LEN ; INC DEST INDEX
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DEX ; DECREMENT COUNTER
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BNE :MVLP ; CONT UNTIL CNT = 0
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DEC :S2LEN ; SUBSTR LEN=FINAL DEST IND-1
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LDA :SCERR ; CHECK FOR ANY ERRORS
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BNE :EREXIT ; BR IF STR TRUNCATED OR OVERFLOW
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:OKEXIT
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CLC
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BCC :EXIT
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:EREXIT
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SEC
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:EXIT
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LDA :S2LEN
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LDY #0
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STA (ADDR2),Y
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STA RETLEN
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RTS
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:S1LEN DS 1
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:S2LEN DS 1
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:MLEN DS 1
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:SCNT DS 1
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:SINDEX DS 1
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:SCERR DS 1
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