59 lines
1.4 KiB
ArmAsm
59 lines
1.4 KiB
ArmAsm
/* memcmp() Author: Kees J. Bot */
|
|
/* 2 Jan 1994 */
|
|
|
|
/* int memcmp(const void *s1, const void *s2, size_t n) */
|
|
/* Compare two chunks of memory. */
|
|
/* */
|
|
.text
|
|
.globl _memcmp
|
|
.balign 16
|
|
_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
|