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