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;
; Ullrich von Bassewitz, 15.09.2000
;
; int memcmp (const void* p1, const void* p2, size_t count);
;
.export _memcmp
.import popax, popptr1, return0
.importzp ptr1, ptr2, ptr3
_memcmp:
; Calculate (-count-1) and store it into ptr3. This is some overhead here but
; saves time in the compare loop
eor #$FF
sta ptr3
txa
eor #$FF
sta ptr3+1
; Get the pointer parameters
jsr popax ; Get p2
sta ptr2
stx ptr2+1
jsr popptr1 ; Get p1
; Loop initialization
;ldy #$00 ; Initialize pointer (Y=0 guaranteed by popptr1)
ldx ptr3 ; Load low counter byte into X
; Head of compare loop: Test for the end condition
Loop: inx ; Bump low byte of (-count-1)
beq BumpHiCnt ; Jump on overflow
; Do the compare
Comp: lda (ptr1),y
cmp (ptr2),y
bne NotEqual ; Jump if bytes not equal
; Bump the pointers
iny ; Increment pointer
bne Loop
inc ptr1+1 ; Increment high bytes
inc ptr2+1
bne Loop ; Branch always (pointer wrap is illegal)
; Entry on low counter byte overflow
BumpHiCnt:
inc ptr3+1 ; Bump high byte of (-count-1)
bne Comp ; Jump if not done
jmp return0 ; Count is zero, areas are identical
; Not equal, check which one is greater
NotEqual:
bcs Greater
ldx #$FF ; Make result negative
rts
Greater:
ldx #$01 ; Make result positive
rts
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