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2008-05-26 Eric Blake <ebb9@byu.net> 

Optimize the generic and x86 strlen.
        * libc/string/strlen.c (strlen) [!__OPTIMIZE_SIZE__]: Pre-align
        data so unaligned searches aren't penalized.
        * libc/machine/i386/strlen.S (strlen) [!__OPTIMIZE_SIZE__]:
        Word operations are faster than repnz byte searches.
This commit is contained in:
Jeff Johnston 2008-05-26 22:56:14 +00:00
parent 12cf19762d
commit cae28869c1
3 changed files with 93 additions and 22 deletions
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8
newlib/ChangeLog
View File

@ -1,3 +1,11 @@
2008-05-26 Eric Blake <ebb9@byu.net>
Optimize the generic and x86 strlen.
* libc/string/strlen.c (strlen) [!__OPTIMIZE_SIZE__]: Pre-align
data so unaligned searches aren't penalized.
* libc/machine/i386/strlen.S (strlen) [!__OPTIMIZE_SIZE__]:
Word operations are faster than repnz byte searches.
2008-05-23 Corinna Vinschen <corinna@vinschen.de>
* libc/include/sys/_default_fcntl.h: Include <sys/time.h> on Cygwin.

65
newlib/libc/machine/i386/strlen.S
View File

@ -1,6 +1,6 @@
/*
* ====================================================
* Copyright (C) 1998, 2002 by Red Hat Inc. All rights reserved.
* Copyright (C) 1998, 2002, 2008 by Red Hat Inc. All rights reserved.
*
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
@ -20,12 +20,75 @@ SYM (strlen):
pushl edi
movl 8(ebp),edx
#ifdef __OPTIMIZE_SIZE__
cld
movl edx,edi
movl $4294967295,ecx
xor eax,eax
repnz
scasb
#else
/* Modern x86 hardware is much faster at double-word
manipulation than with bytewise repnz scasb. */
/* Do byte-wise checks until string is aligned. */
movl edx,edi
test $3,edi
je L5
movb (edi),cl
incl edi
testb cl,cl
je L15
test $3,edi
je L5
movb (edi),cl
incl edi
testb cl,cl
je L15
test $3,edi
je L5
movb (edi),cl
incl edi
testb cl,cl
je L15
L5:
subl $4,edi
/* loop performing 4 byte mask checking for desired 0 byte */
.p2align 4,,7
L10:
addl $4,edi
movl (edi),ecx
leal -16843009(ecx),eax
notl ecx
andl ecx,eax
testl $-2139062144,eax
je L10
/* Find which of four bytes is 0. */
notl ecx
incl edi
testb cl,cl
je L15
incl edi
shrl $8,ecx
testb cl,cl
je L15
incl edi
shrl $8,ecx
testb cl,cl
je L15
incl edi
#endif
L15:
subl edx,edi
leal -1(edi),eax

42
newlib/libc/string/strlen.c
View File

@ -1,7 +1,7 @@
/*
/*
FUNCTION
<<strlen>>---character string length
INDEX
strlen
@ -57,32 +57,32 @@ size_t
_DEFUN (strlen, (str),
_CONST char *str)
{
#if defined(PREFER_SIZE_OVER_SPEED) || defined(__OPTIMIZE_SIZE__)
_CONST char *start = str;
while (*str)
str++;
return str - start;
#else
_CONST char *start = str;
#if !defined(PREFER_SIZE_OVER_SPEED) && !defined(__OPTIMIZE_SIZE__)
unsigned long *aligned_addr;
if (!UNALIGNED (str))
/* Align the pointer, so we can search a word at a time. */
while (UNALIGNED (str))
{
/* If the string is word-aligned, we can check for the presence of
a null in each word-sized block. */
aligned_addr = (unsigned long*)str;
while (!DETECTNULL (*aligned_addr))
aligned_addr++;
/* Once a null is detected, we check each byte in that block for a
precise position of the null. */
str = (char*)aligned_addr;
if (!*str)
return str - start;
str++;
}
/* If the string is word-aligned, we can check for the presence of
a null in each word-sized block. */
aligned_addr = (unsigned long *)str;
while (!DETECTNULL (*aligned_addr))
aligned_addr++;
/* Once a null is detected, we check each byte in that block for a
precise position of the null. */
str = (char *) aligned_addr;
#endif /* not PREFER_SIZE_OVER_SPEED */
while (*str)
str++;
return str - start;
#endif /* not PREFER_SIZE_OVER_SPEED */
}