mirror of
https://github.com/nathanriggs/AppleIIAsm-Collection.git
synced 2024-11-24 07:31:09 +00:00
82 lines
1.9 KiB
Plaintext
82 lines
1.9 KiB
Plaintext
SUBDEL
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PLA
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TAY
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PLA
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TAX
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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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TXA
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PHA
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TYA
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PHA
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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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LDA :SCNT
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BEQ :OKEXIT
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LDA :SINDEX
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BEQ :ERREXIT ; ERR EXIT IF START = 0
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LDA :S1LEN
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CMP :SINDEX
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BCC :ERREXIT
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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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STA :SIDX ; SAVE INDEX + COUNT AS
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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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BEQ :TRUNC ; TRUNC BUT NO ERROR--
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LDA #$0FF
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STA :SCERR ; INDICATE ERROR - NOT
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:TRUNC
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LDX :SINDEX ; STRING LENGTH =
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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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:CNTOK
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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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: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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STX :S1LEN
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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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: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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: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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