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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.

#

.intel_syntax

.globl _memcmp

        .text

	.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

        cmpsd                   # 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

        cmpsw                   # 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