/*
* 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 2005 Sun Microsystems, Inc. All rights reserved.
* Use is subject to license terms.
*/
/
/ strlen(s)
/
/
/
/
/ size_t
/ strlen(const char *s)
/ {
/ const char *s0 = s + 1;
/
/ while (*s++ != '\0')
/ ;
/ return (s - s0);
/ }
/
/ 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.
/
#include "SYS.h"
ENTRY(strlen)
mov 4(%esp), %edx / src in %edx
mov %edx, %eax / cpy src to %eax
and $3, %edx / is src aligned?
jz countbytes
/ work byte-wise until aligned
cmpb $0, (%eax) / is *src == 0 ?
jz done
inc %eax / increment src
cmp $3, %edx / if aligned, jump to word-wise check
jz countbytes
cmpb $0, (%eax)
jz done
inc %eax
cmp $2, %edx
jz countbytes
cmpb $0, (%eax)
jz done
inc %eax
.align 16
countbytes:
mov (%eax), %ecx / load wrd
add $4, %eax / increment src by 4 (bytes in word)
lea -0x01010101(%ecx), %edx / (wrd - 0x01010101)
not %ecx / ~wrd
and $0x80808080, %ecx / ~wrd & 0x80808080
and %edx, %ecx / (wrd - 0x01010101) & ~wrd & 0x80808080
jz countbytes / if zero, no null byte found -- cont
has_zero_byte:
bsfl %ecx, %ecx / find first set bit (null byte)
shr $3, %ecx / switch bit position to byte posn
lea -4(%eax, %ecx, 1), %eax / undo pre-increment and count bytes
done:
sub 4(%esp), %eax / return (src - old_src)
ret
SET_SIZE(strlen)