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;
; Ullrich von Bassewitz, 25.05.2000
;
; int strncmp (const char* s1, const char* s2, unsigned n);
;
.export _strncmp
.import popax, popptr1
.importzp ptr1, ptr2, ptr3
_strncmp:
; Convert the given counter value in a/x from a downward counter into an
; upward counter, so we can increment the counter in the loop below instead
; of decrementing it. This adds some overhead now, but is cheaper than
; executing a more complex test in each iteration of the loop. We do also
; correct the value by one, so we can do the test on top of the loop.
eor #$FF
sta ptr3
txa
eor #$FF
sta ptr3+1
; Get the remaining arguments
jsr popax ; get s2
sta ptr2
stx ptr2+1
jsr popptr1 ; get s1
; Loop setup
;ldy #0 Y=0 guaranteed by popptr1
; Start of compare loop. Check the counter.
Loop: inc ptr3
beq IncHi ; Increment high byte
; Compare a byte from the strings
Comp: lda (ptr1),y
cmp (ptr2),y
bne NotEqual ; Jump if strings different
tax ; End of strings?
beq Equal1 ; Jump if EOS reached, a/x == 0
; Increment the pointers
iny
bne Loop
inc ptr1+1
inc ptr2+1
bne Loop ; Branch always
; Increment hi byte
IncHi: inc ptr3+1
bne Comp ; Jump if counter not zero
; Exit code if strings are equal. a/x not set
Equal: lda #$00
tax
Equal1: rts
; Exit code if strings not equal
NotEqual:
bcs L1
ldx #$FF ; Make result negative
rts
L1: ldx #$01 ; Make result positive
rts
|
