mirror of
https://github.com/nathanriggs/AppleIIAsm-Collection.git
synced 2024-11-23 15:32:08 +00:00
193 lines
4.7 KiB
Plaintext
193 lines
4.7 KiB
Plaintext
*
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*``````````````````````````````*
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* SUBDEL :: DELETE SUBSTRING *
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*- -*
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* DELETE A SUBSTRING FROM A *
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* STRING. *
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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 ; STRING ADDRESS *
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* PHA *
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* LDA #<STR *
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* PHA *
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* LDA IND ; DEL START INDEX *
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* PHA *
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* LDA LEN ; LENGTH OF DELETE *
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* PHA *
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* JSR SUBDEL *
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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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* NUMBER OF BYTES TO DELETE *
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* STARTING INDEX OF DELETION *
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* LO BYTE OF STRING ADDRESS *
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* HI BYTE OF STRING 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 = TRASH *
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* .X = TRASH *
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* .A = TRASH *
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* *
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* IF NO ERRORS, CARRY = 0; *
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* 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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SUBDEL
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*
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** SAVE RETURN ADDRES
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*
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PLA
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TAY
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PLA
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TAX
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*
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** GET PARAMTERS
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*
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PLA
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STA :SCNT
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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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** RESTORE RETURN ADDRESS
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*
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TXA
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PHA
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TYA
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PHA
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*
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** INITIALIZE ERROR INDICATOR TO 0
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*
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LDY #0
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STY :SCERR
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LDA (ADDR1),Y
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STA :S1LEN ; GET STRING LENGTH
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*
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** CHECK FOR A NON-ZERO COUNT AND INDEX
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*
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LDA :SCNT
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BEQ :OKEXIT
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; GOOD EXIT IF NO DELETE
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LDA :SINDEX
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BEQ :ERREXIT ; ERR EXIT IF START = 0
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*
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** CHECK FOR STARTING INDEX WITHIN THE STRING
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*
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* EXIT IF IT IS NOT
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*
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LDA :S1LEN
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CMP :SINDEX
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BCC :ERREXIT
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*
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** BE SURE THE NUMBER OF CHARACTERS REQUESTED
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** TO BE DELETED ARE PRESENT.
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** IF NOT, THEN ONLY DELETE FROM THE INDEX
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** TO THE END OF THE STRING.
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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 :TRUNC ;TRUNCATE IF INDEX
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; + COUNT > 255
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STA :SIDX ; SAVE INDEX + COUNT AS
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; THE SOURCE INDEX
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TAX ; X = INDEX + COUNT
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DEX
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CPX :S1LEN
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BCC :CNTOK ; BR IF IND + CNT - 1
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; < __S1LEN
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; ELSE JUST TRUNC STRING
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BEQ :TRUNC ; TRUNC BUT NO ERROR--
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; EXACTLY ENOUGH CHARS
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LDA #$0FF
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STA :SCERR ; INDICATE ERROR - NOT
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; ENOUGH CHARS TO DELETE
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*
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** TRUNCATE THE STRING - NO COMPACTING NECESSARY
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*
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:TRUNC
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LDX :SINDEX ; STRING LENGTH =
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; START INDEX - 1
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DEX
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STX :S1LEN
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LDA :SCERR
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BEQ :OKEXIT
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BNE :ERREXIT
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*
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** DELETE THE SUBSTRING BY COMPACTING
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** MOVE ALL CHARS ABOVE THE DELETED AREA DOWN
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*
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:CNTOK
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*
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** CALCULATE NUMBER OF CHARS TO MOVE
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** (SLEN - SIDX + 1)
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*
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LDA :S1LEN ; GET STR LENGTH
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SEC
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SBC :SIDX ; SUBTRACT START INDEX
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TAX
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INX
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BEQ :OKEXIT ; ADD 1 TO INCLUDE LAST
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; CHAR; BR IF CNT = 0
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:MVLP
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LDY :SIDX
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LDA (ADDR1),Y ; GET NEXT CHAR
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LDY :SINDEX
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STA (ADDR1),Y ;MOVE IT DOWN
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INC :SINDEX
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INC :SIDX ; INC DEST, SRC INDEXES
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DEX
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BNE :MVLP ; CONT UNTIL CNT = 0
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LDX :SINDEX
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DEX ; START LENGTH = FINAL
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; DEST INDEX -1
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STX :S1LEN
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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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:ERREXIT
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SEC
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*
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:EXIT
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LDA :S1LEN
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LDY #0
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STA (ADDR1),Y ; SET LENGTH OF STRING
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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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:SCNT DS 1
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:SINDEX DS 1
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:SIDX DS 1
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:SCERR DS 1
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*
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