/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright 2004 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

        .file   "memcmp.s"

/
/ memcmp(s1, s2, n)
/
/ Compares n bytes:  s1>s2: >0  s1==s2:  0  s1<s2:  <0
/
/ Fast assembly language version of the following C-program strcat
/ which represents the `standard' for the C-library.
/
/       int
/       memcmp(const void *s1, const void *s2, size_t n)
/       {
/               if (s1 != s2 && n != 0) {
/                       const unsigned char     *ps1 = s1;
/                       const unsigned char     *ps2 = s2;
/
/                       do {
/                               if (*ps1++ != *ps2++)
/                                       return (ps1[-1] - ps2[-1]);
/                       } while (--n != 0);
/               }
/               return (NULL);
/       }
/
/ This implementation conforms to SVID but does not implement
/ the same algorithm as the portable version because it is
/ inconvenient to get the difference of the differing characters.

#include <sys/asm_linkage.h>

        ANSI_PRAGMA_WEAK(memcmp,function)

#include "SYS.h"

        ENTRY(memcmp)
        pushl   %edi            / save register variable
        movl    8(%esp), %eax   / %eax = address of string 1
        movl    12(%esp), %ecx  / %ecx = address of string 2
        cmpl    %eax, %ecx      / if the same string
        je      .equal          / goto .equal
        movl    16(%esp), %edi  / %edi = length in bytes
        cmpl    $4, %edi        / if %edi < 4
        jb      .byte_check     / goto .byte_check
        .align  4
.word_loop:
        movl    (%ecx), %edx    / move 1 word from (%ecx) to %edx
        leal    -4(%edi), %edi  / %edi -= 4
        cmpl    (%eax), %edx    / compare 1 word from (%eax) with %edx
        jne     .word_not_equal / if not equal, goto .word_not_equal
        leal    4(%ecx), %ecx   / %ecx += 4 (next word)
        leal    4(%eax), %eax   / %eax += 4 (next word)
        cmpl    $4, %edi        / if %edi >= 4
        jae     .word_loop      / goto .word_loop
.byte_check:
        cmpl    $0, %edi        / if %edi == 0
        je      .equal          / goto .equal
        jmp     .byte_loop      / goto .byte_loop (checks in bytes)
.word_not_equal:
        leal    4(%edi), %edi   / %edi += 4 (post-decremented)
        .align  4
.byte_loop:
        movb    (%ecx), %dl     / move 1 byte from (%ecx) to %dl
        cmpb    %dl, (%eax)     / compare %dl with 1 byte from (%eax)
        jne     .not_equal      / if not equal, goto .not_equal
        incl    %ecx            / %ecx++ (next byte)
        incl    %eax            / %eax++ (next byte)
        decl    %edi            / %edi--
        jnz     .byte_loop      / if not zero, goto .byte_loop
.equal:
        xorl    %eax, %eax      / %eax = 0
        popl    %edi            / restore register variable
        ret                     / return (NULL)
        .align  4
.not_equal:
        sbbl    %eax, %eax      / %eax = 0 if no carry, %eax = -1 if carry
        orl     $1, %eax        / %eax = 1 if no carry, %eax = -1 if carry
        popl    %edi            / restore register variable
        ret                     / return (NULL)
        SET_SIZE(memcmp)