mirror of
https://github.com/nathanriggs/AppleIIAsm-Collection.git
synced 2024-11-27 12:49:27 +00:00
172 lines
4.3 KiB
Plaintext
172 lines
4.3 KiB
Plaintext
*
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*``````````````````````````````*
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* SUBPOS :: SUBSTRING POSITION *
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*- -*
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* FIND THE POSITION OF A SUB- *
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* STRING WITHIN ANOTHER 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 ADDR *
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* PHA *
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* LDA #<STR *
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* PHA *
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* LDA #>SUB ; SUBSTR ADDR *
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* PHA *
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* LDA #<SUB *
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* JSR SUBPOS *
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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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* LOW BYTE OF SUBSTRING ADDR *
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* HI BYTE OF SUBSTRING ADDR *
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* LO BYTE OF STRING ADDR *
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* HI BYTE OF STRING 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 = CLOBBERED; TRASH *
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* .X = CLOBBERED; TRASH *
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* .A = INDEX OF SUBSTRING IF *
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* FOUND; OTHERWISE, 0 *
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* *
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* [RETURN] = INDEX OF SUBSTR; *
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* 0 IF NOT FOUND *
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* [RETLEN] = 1 (INDEX LENGTH) *
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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/. MAY NOT *
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* FALL UNDER APACHE 2.0 UNTIL *
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* HEAVILY MODIFIED. *
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*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
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*
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SUBPOS
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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 ADDR2
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PLA
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STA ADDR2+1
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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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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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:POS
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LDY #0
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LDA (ADDR1),Y ; GET LENGTH OF STRING
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BEQ :NOTFND ; EXIT IF LENGTH = 0
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STA :SLEN
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LDA (ADDR2),Y ; GET SUBSTR LENGTH
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BEQ :NOTFND ; EXIT IF SUB LENGTH = 0
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STA :SUBLEN
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*
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** IF THE SUBSTR IS LONGER THAN STR, DECLARE THE
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** SUBSTR NOT FOUND
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*
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LDA :SUBLEN
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CMP :SLEN
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BEQ :LENOK
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BCS :NOTFND ; CANNOT FIND SUBSTR IF
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; LONGER THAN STR
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*
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** START, SEARCH, CONTINUE UNTIL
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** REMAINING STR SHORTER THAN SUBSTR
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*
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:LENOK
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LDA #1
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STA :SINDEX ; START LOOKING AT FIRST
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; CHARACTER OF STRING
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LDA :SLEN ; CONT UNTIL REMAINING STR
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; TOO SHORT
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SEC ; COUNT=STR LEN - SUB LEN+1
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SBC :SUBLEN
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STA :SCOUNT
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INC :SCOUNT
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*
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** SEARCH FOR SUBSTRING IN STRING
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*
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:SLP1
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LDA :SINDEX
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STA :SIDX ; START STR AT INDEX
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LDA #1
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STA :SUBIDX ; START SUB IND AT 1
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*
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** LOOK FOR SUBSTRING BEGINNING AT INDEX
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*
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:CMPLP
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LDY :SIDX
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LDA (ADDR1),Y ; GET NEXT CHAR FROM STR
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LDY :SUBIDX
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CMP (ADDR2),Y ; COMPARE TO NEXT SUB CHAR
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BNE :SLP2 ; BR IF SUB NOT HERE
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LDY :SUBIDX
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CPY :SUBLEN ; TEST IF WE ARE DONE
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BEQ :FOUND ; BR IF ALL CHARS WERE EQUAL
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INY ; ELSE INC TO NEXT CHAR
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STY :SUBIDX
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INC :SIDX
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JMP :CMPLP ; CONTINUE
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*
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** ARRIVE HERE IF SUBSTRING NOT FOUND
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*
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:SLP2
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INC :SINDEX ; INCREMENT INDEX
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DEC :SCOUNT ; DEC COUNT
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BNE :SLP1 ; BR IF NOT DONE
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BEQ :NOTFND ; ELSE EXIT TO NOT FOUND
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*
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:FOUND
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LDA :SINDEX ; FOUND, A = STARTING IDX
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JMP :EXIT
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*
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:NOTFND
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LDA #0 ; SUB NOT FOUND, A=0
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:EXIT
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STA RETURN
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LDY #1
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STY RETLEN
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RTS
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*
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** DATA
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*
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:SLEN DS 1
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:SUBLEN DS 1
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:SINDEX DS 1
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:SUBIDX DS 1
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:SCOUNT DS 1
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:SIDX DS 1
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*
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