lib/libc/i386/string/bzero.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: bzero.s,v 1.6 1993/08/16 17:06:29 jtc Exp $
 */

#if defined(LIBC_RCS) && !defined(lint)
        .asciz "$Id: bzero.s,v 1.6 1993/08/16 17:06:29 jtc Exp $"
#endif /* LIBC_RCS and not lint */

#include "DEFS.h"

/*
 * bzero (void *b, size_t len)
 *      write len zero bytes to the string b.
 *
 * Written by:
 *      J.T. Conklin (jtc@wimsey.com), Winning Strategies, Inc.
 */

ENTRY(bzero)
        pushl   %edi
        pushl   %ebx
        movl    12(%esp),%edi
        movl    16(%esp),%ecx

        cld                             /* set fill direction forward */
        xorl    %eax,%eax               /* set fill data to 0 */

        /*
         * if the string is too short, it's really not worth the overhead
         * of aligning to word boundries, etc.  So we jump to a plain
         * unaligned set.
         */
        cmpl    $0x0f,%ecx
        jle     L1

        movl    %edi,%edx               /* compute misalignment */
        negl    %edx
        andl    $3,%edx
        movl    %ecx,%ebx
        subl    %edx,%ebx

        movl    %edx,%ecx               /* zero until word aligned */
        rep
        stosb

        movl    %ebx,%ecx               /* zero by words */
        shrl    $2,%ecx
        rep
        stosl

        movl    %ebx,%ecx
        andl    $3,%ecx                 /* zero remainder by bytes */
L1:     rep
        stosb

        popl    %ebx
        popl    %edi
        ret