memcmp.s revision 9a70fc3be3b1e966bf78825cdb8d509963a6f0a1
/*
* 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
* 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.
*/
/
/
/
/
/ 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)