mirror of
https://github.com/nathanriggs/AppleIIAsm-Collection.git
synced 2024-12-11 09:49:17 +00:00
213 lines
5.5 KiB
Plaintext
213 lines
5.5 KiB
Plaintext
*
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*``````````````````````````````*
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* SUBCOPY :: COPY SUBSTRING *
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*- -*
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* COPY A SUBSTRING FROM A *
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* STRING TO [RETURN]. *
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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 #>STR ; SOURCE STRING *
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* PHA *
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* LDA #<STR *
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* PHA *
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* LDA #IND ; COPY START INDEX *
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* PHA *
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* LDA LEN ; LENGTH OF SUBSTR *
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* PHA *
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* LDA MLEN ; MAX LENGTH *
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* PHA *
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* JSR SUBCOPY *
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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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* MAX LENGTH OF DEST STRING *
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* NUMBER OF BYTES TO COPY *
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* STARTING INDEX TO COPY FROM *
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* LO BYTE OF SRC STRING ADDR *
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* HI BYTE OF SOURCE STR ADDR *
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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 = TRASH *
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* .X = TRASH *
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* .A = TRASH *
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* *
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* CARRY FLAG WILL BE 0 IF NO *
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* ERRORS; ELSE, CARRY = 1 *
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*- -*
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* ADAPTED FROM LEVANTHAL AND *
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* WINTHROP'S /6502 ASSEMBLY *
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* LANGUAGE ROUTINES/. *
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*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
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*
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SUBCOPY
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*
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** SAVE 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 :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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*
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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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*
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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 #0
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STA :S2LEN ; DESTINATION LENGTH = 0
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STA :SCERR ; ASSUME NO ERRORS
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*
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** CHECK FOR ZERO BYTES TO COPY OR ZERO MAX SUBSTR LENGTH
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*
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LDA :SCNT
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BEQ :OKEXIT ; BR IF 0 BYTES TO COPY,
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; S2A WILL JUST HAVE ZERO LENGTH
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LDA :MLEN
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BEQ :EREXIT ; ERROR EXIT IF SUBSTR HAS
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; ZERO MAX LENGTH
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LDA :SINDEX
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BEQ :EREXIT ; ERROR EXIT IF START IDX = 0
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*
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** CHECK IF SRC STR REACHES STARTING INDEX
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*
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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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*
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** CHECK THAT WE DO NOT COPY BEYOND THE END OF
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** THE SOURCE STRING.
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** IF INDEX + COUNT -1 > SLEN THEN
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** COUNT = SLEN - SINDEX + 1
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*
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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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*
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** THE CALLER ASKED FOR TOO MANY CHARS SO
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** JUST RETURN EVERYTHING BETWEEN INDEX AND
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** END OF STRING. SO CNT = S1LEN - INDEX + 1
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*
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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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*
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** CHECK IF COUNT IS <= THE MAXIMUM LENGTH
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** OF THE DEST STRING. IF NOT, THEN SET COUNT TO
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** MAX LENGTH.
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** IF COUNT > MAXLEN THEN
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** COUNT = MAXLEN
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*
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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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*
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** EVERYTHING IS SET UP SO MOVE THE
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** SUBSTRING TO THE DESTINATION STRING
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*
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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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*
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** GOOD EXIT
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*
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:OKEXIT
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CLC
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BCC :EXIT
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*
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** ERROR EXIT
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*
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:EREXIT
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SEC
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*
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** STORE LENGTH BYTE IN FRONT OF SUBSTR
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*
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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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*
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** DATA
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*
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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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*
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