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/*
* 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 "strncpy.s"
/
/ strncpy(s1, s2, n)
/
/ Copies s2 to s1, truncating or null-padding to always copy n bytes
/ Returns s1
/
/ Fast assembly language version of the following C-program strncpy
/ which represents the `standard' for the C-library.
/
/ char *
/ strncpy(char *s1, const char *s2, size_t n)
/ {
/ char *os1 = s1;
/
/ n++;
/ while ((--n != 0) && ((*s1++ = *s2++) != '\0'))
/ ;
/ if (n != 0)
/ while (--n != 0)
/ *s1++ = '\0';
/ return (os1);
/ }
/
/ In this assembly language version, the following expression is used
/ to check if a 32-bit word data contains a null byte or not:
/ (((A & 0x7f7f7f7f) + 0x7f7f7f7f) | A) & 0x80808080
/ If the above expression geneates a value other than 0x80808080,
/ that means the 32-bit word data contains a null byte.
/
/ Assume relatively long strings and small numbers of nulls at end.
#include "SYS.h"
ENTRY(strncpy)
pushl %edi / save register variables
pushl %esi
movl 16(%esp), %eax / %eax = source string address
movl 12(%esp), %edi / %edi = destination string address
movl 20(%esp), %esi / %esi = number of bytes
testl $3, %eax / if %eax not word aligned
jnz .L1 / goto .L1
.L8:
cmpl $4, %esi / if number of bytes < 4
jb .L4 / goto .L4
.align 4
.L2:
movl (%eax), %edx / move 1 word from (%eax) to %edx
movl $0x7f7f7f7f, %ecx
andl %edx, %ecx / %ecx = %edx & 0x7f7f7f7f
addl $4, %eax / next word
addl $0x7f7f7f7f, %ecx / %ecx += 0x7f7f7f7f
orl %edx, %ecx / %ecx |= %edx
andl $0x80808080, %ecx / %ecx &= 0x80808080
cmpl $0x80808080, %ecx / if null byte in this word
jne .L3 / goto .L3
movl %edx, (%edi) / copy this word to (%edi)
subl $4, %esi / decrement number of bytes by 4
addl $4, %edi / next word
cmpl $4, %esi / if number of bytes >= 4
jae .L2 / goto .L2
jmp .L4 / goto .L4
.L3:
subl $4, %eax / post-incremented
.align 4
.L4:
/ (number of bytes < 4) or (a null byte found in the word)
cmpl $0, %esi / if number of bytes == 0
je .L7 / goto .L7 (finished)
movb (%eax), %dl / %dl = a byte in (%eax)
decl %esi / decrement number of bytes by 1
movb %dl, (%edi) / copy %dl to (%edi)
incl %eax / next byte
incl %edi / next byte
cmpb $0, %dl / compare %dl with a null byte
je .L5 / if %dl is a null, goto .L5
jmp .L4 / goto .L4
.align 4
.L1:
/ %eax not aligned
cmpl $0, %esi / if number of bytes == 0
je .L7 / goto .L7 (finished)
movb (%eax), %dl / %dl = a byte in (%eax)
decl %esi / decrement number of bytes by 1
movb %dl, (%edi) / copy %dl to (%edi)
incl %edi / next byte
incl %eax / next byte
cmpb $0, %dl / compare %dl with a null byte
je .L5 / if %dl is a null, goto .L5
testl $3, %eax / if %eax word aligned
jz .L8 / goto .L8
jmp .L1 / goto .L1 (not word aligned)
.align 4
.L5:
movl %esi, %ecx / %ecx = length to copy null bytes
xorl %eax, %eax / clear %eax
shrl $2, %ecx / %ecx = words to copy null bytes
rep ; sstol / rep;sstol is optimal
andl $3, %esi / %esi = leftover bytes
.L6:
cmpl $0, %esi / if number of bytes == 0
jz .L7 / goto .L7 (finished)
movb $0, (%edi) / move a null byte to (%edi)
decl %esi / decrement number of bytes by 1
incl %edi / next byte
jmp .L6 / goto .L6
.align 4
.L7:
movl 12(%esp), %eax / return the destination address
popl %esi / restore register variables
popl %edi
ret
SET_SIZE(strncpy)
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