minix/lib/libc/arch/i386/string/memcmp.S

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/* memcmp() Author: Kees J. Bot */
/* 2 Jan 1994 */
/* int memcmp(const void *s1, const void *s2, size_t n) */
/* Compare two chunks of memory. */
/* */
#include <machine/asm.h>
ENTRY(memcmp)
cld
push %ebp
movl %esp, %ebp
push %esi
push %edi
movl 8(%ebp), %esi /* String s1 */
movl 12(%ebp), %edi /* String s2 */
movl 16(%ebp), %ecx /* Length */
cmpl $16, %ecx
jb cbyte /* Don't bother being smart with short arrays */
movl %esi, %eax
orl %edi, %eax
testb $1, %al
jne cbyte /* Bit 0 set, use byte compare */
testb $2, %al
jne cword /* Bit 1 set, use word compare */
clword:
shrdl $2, %ecx, %eax /* Save low two bits of ecx in eax */
shrl $2, %ecx
repe cmpsl /* Compare longwords */
subl $4, %esi
subl $4, %edi
incl %ecx /* Recompare the last longword */
shldl $2, %eax, %ecx /* And any excess bytes */
jmp last
cword:
shrdl $1, %ecx, %eax /* Save low bit of ecx in eax */
shrl $1, %ecx
repe cmpsw /* Compare words */
subl $2, %esi
subl $2, %edi
incl %ecx /* Recompare the last word */
shldl $1, %eax, %ecx /* And one more byte? */
cbyte:
testl %ecx, %ecx /* Set 'Z' flag if ecx = 0 */
last:
repe cmpsb /* Look for the first differing byte */
seta %al /* al = (s1 > s2) */
setb %ah /* ah = (s1 < s2) */
subb %ah, %al
movsbl %al, %eax /* eax = (s1 > s2) - (s1 < s2), i.e. -1, 0, 1 */
movl %esi, %edx /* For bcmp() to play with */
pop %edi
pop %esi
pop %ebp
ret