minix/lib/i86/string/memcmp.s
2005-04-21 14:53:53 +00:00

44 lines
981 B
ArmAsm
Executable file

! memcmp() Author: Kees J. Bot
! 27 Jan 1994
.sect .text; .sect .rom; .sect .data; .sect .bss
! int memcmp(const void *s1, const void *s2, size_t n)
! Compare two chunks of memory.
!
.sect .text
.define _memcmp
_memcmp:
cld
push bp
mov bp, sp
push si
push di
xor ax, ax ! Prepare return value
mov si, 4(bp) ! String s1
mov di, 6(bp) ! String s2
mov cx, 8(bp) ! Length
cmp cx, #16
jb cbyte ! Don't bother being smart with short arrays
mov dx, si
or dx, di
andb dl, #1
jnz cbyte ! Bit 0 set, use byte compare
cword: sar cx, #1
adcb dl, dl ! Save carry
repe cmps ! Compare words
mov cx, #2 ! Recompare the last word
sub si, cx
sub di, cx
addb cl, dl ! One more byte?
cbyte: test cx, cx ! Set 'Z' flag if cx = 0
last:
repe cmpsb ! Look for the first differing byte
je equal
ja after
sub ax, #2 ! if (s1 < s2) ax -= 2;
after: inc ax ! ax++, now it's -1 or 1
equal: mov dx, si ! For bcmp() to play with
pop di
pop si
pop bp
ret