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;
; Ullrich von Bassewitz, 11.12.1998
;
; char* strstr (const char* haystack, const char* needle);
;
.export _strstr
.import popptr1
.importzp ptr1, ptr2, ptr3, ptr4, tmp1
_strstr:
sta ptr2 ; Save needle
stx ptr2+1
sta ptr4 ; Setup temp copy for later
jsr popptr1 ; Get haystack to ptr1
; If needle is empty, return haystack
; ldy #$00 Y=0 guaranteed by popptr1
lda (ptr2),y ; Get first byte of needle
beq @Found ; Needle is empty --> we're done
; Search for the beginning of the string (this is not an optimal search
; strategy [in fact, it's pretty dumb], but it's simple to implement).
sta tmp1 ; Save start of needle
@L1: lda (ptr1),y ; Get next char from haystack
beq @NotFound ; Jump if end
cmp tmp1 ; Start of needle found?
beq @L2 ; Jump if so
iny ; Next char
bne @L1
inc ptr1+1 ; Bump high byte
bne @L1 ; Branch always
; We found the start of needle in haystack
@L2: tya ; Get offset
clc
adc ptr1
sta ptr1 ; Make ptr1 point to start
bcc @L3
inc ptr1+1
; ptr1 points to the start of needle now. Setup temporary pointers for the
; search. The low byte of ptr4 is already set.
@L3: sta ptr3
lda ptr1+1
sta ptr3+1
lda ptr2+1
sta ptr4+1
ldy #1 ; First char is identical, so start on second
; Do the compare
@L4: lda (ptr4),y ; Get char from needle
beq @Found ; Jump if end of needle (-> found)
cmp (ptr3),y ; Compare with haystack
bne @L5 ; Jump if not equal
iny ; Next char
bne @L4
inc ptr3+1
inc ptr4+1 ; Bump hi byte of pointers
bne @L4 ; Next char (branch always)
; The strings did not compare equal, search next start of needle
@L5: ldy #1 ; Start after this char
bne @L1 ; Branch always
; We found the start of needle
@Found: lda ptr1
ldx ptr1+1
rts
; We reached end of haystack without finding needle
@NotFound:
lda #$00 ; return NULL
tax
rts
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