AppleIIAsm-Collection/disks/disk5_strings/T.STRCMP

*
*``````````````````````````````*
* STRCMP ::     STRING COMPARE *
*-                            -*
* COMPARE TWO STRINGS AND      *
* DETERMINE IF THEY ARE        *
* IDENTICAL; IF NOT, DETERMINE *
* WHICH IS THE SHORTEST AND    *
* WHICH IS THE LONGEST.        *
*                              *
* Z FLAG = 1 IF IDENTICAL      *
* Z FLAG = 0 IF NOT            *
* CARRY = 1 IF STR2 > STR1 LEN *
* CARRY = 0 IF STR1 > STR2 LEN *
*-                            -*
* CLOBBERS:                    *
*                              *
* FLAGS:  ????----  REG: AXYM  *
*-                            -*
* CYCLES: ???                  *
* SIZE:                        *
*-                            -*
* USAGE:                       *
*                              *
*   LDA #>STR1                 *
*   PHA                        *
*   LDA #<STR1                 *
*   PHA                        *
*   LDA #>STR2                 *
*   PHA                        *
*   LDA #<STR2                 *
*   PHA                        *
*   JSR STRCMP                 *
*                              *
* STR1 STR "STRING1 "          *
* STR2 STR "ZTRING2"           *
*-                            -*
* ENTRY                        *
*                              *
* TOP OF STACK                 *
*                              *
* LOW BYTE OF RETURN ADDRESS   *
* HI BYTE OF RETURN ADDRESS    *
* STRING 2 ADDRESS LOW BYTE    *
* STRING 2 ADDRESS HI BYTE     *
* STRING 1 ADDRESS LOW BYTE    *
* STRING 1 ADDRESS HI BYTE     *
*-                            -*
* EXIT                         *
*                              *
* TOP OF STACK                 *
*                              *
* LOW BYTE OF RETURN ADDRESS   *
* HI BYTE OF RETURN ADDRESS    *
*                              *
* .Y = LENGTH OF STRING 2      *
* .X = LENGTH OF STRING 1      *
* .A = CLOBBERED; TRASH        *
*-                            -*
* ADAPTED FROM LEVANTHAL AND   *
* WINTHROP'S /6502 ASSEMBLY    *
* LANGUAGE ROUTINES/. MAY NOT  *
* FALL UNDER APACHE 2.0 UNTIL  *
* SUBSTANTIALLY ALTERED.       *
*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
*
STRCMP
*
** SAVE RETURN ADDRESS
*
         PLA
         STA   RETADR
         PLA
         STA   RETADR+1
*
** GET PARAMETERS
*
         PLA
         STA   ADDR2
         PLA
         STA   ADDR2+1
         PLA
         STA   ADDR1
         PLA
         STA   ADDR1+1
*
         LDY   #0
         LDA   (ADDR1),Y  ; GET LENGTH OF STRING 1
         CMP   (ADDR2),Y
         BCC   :BEGCMP    ; IF STRING 2 IS SHORTER THEN
         LDA   (ADDR2),Y  ; USE ITS LENGTH INSTEAD
*
** COMPARE THE STRINGS THROUGH THE
** LENGTH OF THE SHORTER STRING
*
:BEGCMP
         TAX              ; X IS LENGTH OF SHORTER STRING
         BEQ   :TSTLEN    ; BR IF LENGTH IS 0
         LDY   #1         ; POINT AT FIRST CHAR OF STRINGS
:CMPLP
         LDA   (ADDR1),Y
         CMP   (ADDR2),Y
         BNE   :EXIT      ; BR IF CHARS NOT EQUAL
                          ; Z,C WILL BE PROPERLY SET
                          ; OR CLEARED
                          ; ELSE
         INY              ; NEXT CHAR
         DEX              ; DECREMENT COUNTER
         BNE   :CMPLP     ; CONTINUE UNTIL ALL BYTES PAIRED
*
* THE 2 STRINGS ARE EQUAL TO LENGTH OF THE SHORTER
* SO USE LENGTHS AS BASIS FOR SETTING THE FLAGS
*
:TSTLEN
         LDY   #0         ; COMPARE LENGTHS
         LDA   (ADDR1),Y
         CMP   (ADDR2),Y  ; SET OR CLEAR THE FLAGS
*
** Z FLAG = 1 IF STRINGS IDENTICAL
** Z FLAG = 0 IF NOT IDENTICAL
** CARRY = 0 IF STR2 LENGTH > STR1 LENGTH
** CARRY = 1 IF STR1 LENGTH >= STR2 LENGTH
*
:EXIT
*
** RESTORE RETURN ADDRESS
*
         LDA   RETADR+1
         PHA
         LDA   RETADR
         PHA
*
         LDY   #0
         LDA   (ADDR1),Y  ; GET STR1 LENGTH
         TAX              ; RETURN IN X
         LDA   (ADDR2),Y  ; STR2 LENGTH
         TAY              ; RETURN IN Y
*
         RTS
*