lib/libc/i386/string/memcmp.S

/*
 * Copyright (c) 1993 Winning Strategies, Inc.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by Winning Strategies, Inc.
 * 4. The name of the author may not be used to endorse or promote products
 *    derived from this software withough specific prior written permission
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 *      $Id: memcmp.S,v 1.2 1994/03/04 19:47:11 ache Exp $
 */

#if defined(LIBC_RCS) && !defined(lint)
        .asciz "$Id: memcmp.S,v 1.2 1994/03/04 19:47:11 ache Exp $"
#endif /* LIBC_RCS and not lint */

#include "DEFS.h"

/*
 * memcmp (void *b1, void *b2, size_t len)
 *
 * Written by:
 *      J.T. Conklin (jtc@wimsey.com), Winning Strategies, Inc.
 */

ENTRY(memcmp)
        pushl   %edi
        pushl   %esi
        movl    12(%esp),%edi
        movl    16(%esp),%esi
        movl    20(%esp),%edx
        cld                             /* set compare direction forward */

        movl    %edx,%ecx               /* compare by words */
        shrl    $2,%ecx
        repe
        cmpsl
        jne     L5                      /* do we match so far? */

        movl    %edx,%ecx               /* compare remainder by bytes */
        andl    $3,%ecx
        repe
        cmpsb
        jne     L6                      /* do we match? */

        xorl    %eax,%eax               /* we match, return zero        */
        popl    %esi
        popl    %edi
        ret

L5:     movl    $4,%ecx                 /* We know that one of the next */
        subl    %ecx,%edi               /* four pairs of bytes do not   */
        subl    %ecx,%esi               /* match.                       */
        repe
        cmpsb
L6:     movzbl  -1(%edi),%eax           /* Perform unsigned comparison  */
        movzbl  -1(%esi),%edx
        subl    %edx,%eax
        popl    %esi
        popl    %edi
        ret