mirror of
https://github.com/nathanriggs/AppleIIAsm-Collection.git
synced 2024-11-24 07:31:09 +00:00
140 lines
3.8 KiB
Plaintext
140 lines
3.8 KiB
Plaintext
*``````````````````````````````*
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* STRCMP :: STRING COMPARE *
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*- -*
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* COMPARE TWO STRINGS AND *
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* DETERMINE IF THEY ARE *
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* IDENTICAL; IF NOT, DETERMINE *
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* WHICH IS THE SHORTEST AND *
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* WHICH IS THE LONGEST. *
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* *
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* Z FLAG = 1 IF IDENTICAL *
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* Z FLAG = 0 IF NOT *
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* CARRY = 1 IF STR2 > STR1 LEN *
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* CARRY = 0 IF STR1 > STR2 LEN *
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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 #>STR1 *
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* PHA *
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* LDA #<STR1 *
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* PHA *
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* LDA #>STR2 *
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* PHA *
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* LDA #<STR2 *
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* PHA *
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* JSR STRCMP *
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* *
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* STR1 STR "STRING1 " *
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* STR2 STR "ZTRING2" *
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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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* STRING 2 ADDRESS LOW BYTE *
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* STRING 2 ADDRESS HI BYTE *
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* STRING 1 ADDRESS LOW BYTE *
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* STRING 1 ADDRESS HI BYTE *
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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 = LENGTH OF STRING 2 *
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* .X = LENGTH OF STRING 1 *
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* .A = CLOBBERED; TRASH *
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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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* SUBSTANTIALLY ALTERED. *
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*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
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*
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STRCMP
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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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LDY #0
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LDA (ADDR1),Y ; GET LENGTH OF STRING 1
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CMP (ADDR2),Y
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BCC :BEGCMP ; IF STRING 2 IS SHORTER THEN
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LDA (ADDR2),Y ; USE ITS LENGTH INSTEAD
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*
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** COMPARE THE STRINGS THROUGH THE
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** LENGTH OF THE SHORTER STRING
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*
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:BEGCMP
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TAX ; X IS LENGTH OF SHORTER STRING
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BEQ :TSTLEN ; BR IF LENGTH IS 0
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LDY #1 ; POINT AT FIRST CHAR OF STRINGS
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:CMPLP
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LDA (ADDR1),Y
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CMP (ADDR2),Y
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BNE :EXIT ; BR IF CHARS NOT EQUAL
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; Z,C WILL BE PROPERLY SET
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; OR CLEARED
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; ELSE
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INY ; NEXT CHAR
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DEX ; DECREMENT COUNTER
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BNE :CMPLP ; CONTINUE UNTIL ALL BYTES PAIRED
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*
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* THE 2 STRINGS ARE EQUAL TO LENGTH OF THE SHORTER
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* SO USE LENGTHS AS BASIS FOR SETTING THE FLAGS
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*
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:TSTLEN
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LDY #0 ; COMPARE LENGTHS
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LDA (ADDR1),Y
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CMP (ADDR2),Y ; SET OR CLEAR THE FLAGS
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*
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** Z FLAG = 1 IF STRINGS IDENTICAL
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** Z FLAG = 0 IF NOT IDENTICAL
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** CARRY = 0 IF STR2 LENGTH > STR1 LENGTH
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** CARRY = 1 IF STR1 LENGTH >= STR2 LENGTH
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*
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:EXIT
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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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LDY #0
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LDA (ADDR1),Y ; GET STR1 LENGTH
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TAX ; RETURN IN X
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LDA (ADDR2),Y ; STR2 LENGTH
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TAY ; RETURN IN Y
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*
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RTS
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*
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