minix/lib/i386/string/memcmp.s
2009-11-09 10:26:00 +00:00

56 lines
1.3 KiB
ArmAsm

! memcmp() Author: Kees J. Bot
! 2 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
.align 16
_memcmp:
cld
push ebp
mov ebp, esp
push esi
push edi
mov esi, 8(ebp) ! String s1
mov edi, 12(ebp) ! String s2
mov ecx, 16(ebp) ! Length
cmp ecx, 16
jb cbyte ! Don't bother being smart with short arrays
mov eax, esi
or eax, edi
testb al, 1
jnz cbyte ! Bit 0 set, use byte compare
testb al, 2
jnz cword ! Bit 1 set, use word compare
clword: shrd eax, ecx, 2 ! Save low two bits of ecx in eax
shr ecx, 2
repe
cmps ! Compare longwords
sub esi, 4
sub edi, 4
inc ecx ! Recompare the last longword
shld ecx, eax, 2 ! And any excess bytes
jmp last
cword: shrd eax, ecx, 1 ! Save low bit of ecx in eax
shr ecx, 1
repe
o16 cmps ! Compare words
sub esi, 2
sub edi, 2
inc ecx ! Recompare the last word
shld ecx, eax, 1 ! And one more byte?
cbyte: test 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 al, ah
movsxb eax, al ! eax = (s1 > s2) - (s1 < s2), i.e. -1, 0, 1
mov edx, esi ! For bcmp() to play with
pop edi
pop esi
pop ebp
ret