memcmp.S revision 1.1 
1/*
2 * Written by J.T. Conklin <jtc@netbsd.org>.
3 * Public domain.
4 * Adapted for NetBSD/x86_64 by Frank van der Linden <fvdl@wasabisystems.com>
5 */
6
7#include <machine/asm.h>
8
9#if defined(LIBC_SCCS)
10	RCSID("$NetBSD: memcmp.S,v 1.1 2001/06/19 00:22:46 fvdl Exp $")
11#endif
12
13ENTRY(memcmp)
14	cld				/* set compare direction forward */
15	movq	%rdx,%rcx		/* compare by longs */
16	shrq	$3,%rcx
17	repe
18	cmpsq
19	jne	L5			/* do we match so far? */
20
21	movq	%rdx,%rcx		/* compare remainder by bytes */
22	andq	$7,%rcx
23	repe
24	cmpsb
25	jne	L6			/* do we match? */
26
27	xorl	%eax,%eax		/* we match, return zero	*/
28	ret
29
30L5:	movl	$8,%ecx			/* We know that one of the next	*/
31	subq	%rcx,%rdi		/* eight pairs of bytes do not	*/
32	subq	%rcx,%rsi		/* match.			*/
33	repe
34	cmpsb
35L6:	xorl	%eax,%eax		/* Perform unsigned comparison	*/
36	movb	-1(%rdi),%al
37	xorl	%edx,%edx
38	movb	-1(%rsi),%dl
39	subl    %edx,%eax
40	ret
41