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Improve generic strspn performance

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As for strcspn, this patch improves strspn performance using a much
faster algorithm.  It first constructs a 256-entry table based on
the accept string and then uses it as a lookup table for the
input string.  As for strcspn optimization, it is generally at least
10 times faster than the existing implementation on bench-strspn
on a few AArch64 implementations.

Also the string/bits/string2.h inlines make no longer sense, as current
implementation will already implement most of the optimizations.

Tested on x86_64, i686, and aarch64.

	* string/strspn.c (strcspn): Rewrite function.
	* string/bits/string2.h (strspn): Use __builtin_strcspn.
	(__strspn_c1): Remove inline function.
	(__strspn_c2): Likewise.
	(__strspn_c3): Likewise.
	* string/string-inlines.c
	[SHLIB_COMPAT(libc, GLIBC_2_1_1, GLIBC_2_24)] (__strspn_c1): Add
	compatibility symbol.
	[SHLIB_COMPAT(libc, GLIBC_2_1_1, GLIBC_2_24)] (__strspn_c2):
	Likewise.
	[SHLIB_COMPAT(libc, GLIBC_2_1_1, GLIBC_2_24)] (__strspn_c3):
	Likewise.
This commit is contained in:
Adhemerval Zanella
2016-03-26 19:09:07 +00:00
parent d3496c9f4f
commit 91f3b75f47
4 changed files with 97 additions and 86 deletions
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57
string/strspn.c
View File

@ -16,32 +16,59 @@
<http://www.gnu.org/licenses/>. */
#include <string.h>
#include <stdint.h>
#undef strspn
#ifndef STRSPN
#define STRSPN strspn
# define STRSPN strspn
#endif
/* Return the length of the maximum initial segment
of S which contains only characters in ACCEPT. */
size_t
STRSPN (const char *s, const char *accept)
STRSPN (const char *str, const char *accept)
{
const char *p;
const char *a;
size_t count = 0;
for (p = s; *p != '\0'; ++p)
if (accept[0] == '\0')
return 0;
if (__glibc_unlikely (accept[1] == '\0'))
{
for (a = accept; *a != '\0'; ++a)
if (*p == *a)
break;
if (*a == '\0')
return count;
else
++count;
const char *a = str;
for (; *str == *accept; str++);
return str - a;
}
return count;
/* Use multiple small memsets to enable inlining on most targets. */
unsigned char table[256];
unsigned char *p = memset (table, 0, 64);
memset (p + 64, 0, 64);
memset (p + 128, 0, 64);
memset (p + 192, 0, 64);
unsigned char *s = (unsigned char*) accept;
/* Different from strcspn it does not add the NULL on the table
so can avoid check if str[i] is NULL, since table['\0'] will
be 0 and thus stopping the loop check. */
do
p[*s++] = 1;
while (*s);
s = (unsigned char*) str;
if (!p[s[0]]) return 0;
if (!p[s[1]]) return 1;
if (!p[s[2]]) return 2;
if (!p[s[3]]) return 3;
s = (unsigned char *) ((uintptr_t)(s) & ~3);
unsigned int c0, c1, c2, c3;
do {
s += 4;
c0 = p[s[0]];
c1 = p[s[1]];
c2 = p[s[2]];
c3 = p[s[3]];
} while ((c0 & c1 & c2 & c3) != 0);
size_t count = s - (unsigned char *) str;
return (c0 & c1) == 0 ? count + c0 : count + c2 + 2;
}
libc_hidden_builtin_def (strspn)