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Improve generic strcspn performance

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Improve strcspn performance using a much faster algorithm.  It is kept simple
so it works well on most targets.  It is generally at least 10 times faster
than the existing implementation on bench-strcspn on a few AArch64
implementations, and for some tests 100 times as fast (repeatedly calling
strchr on a small string is extremely slow...).

In fact the string/bits/string2.h inlines make no longer sense, as GCC
already uses strlen if reject is an empty string, strchrnul is 5 times as
fast as __strcspn_c1, while __strcspn_c2 and __strcspn_c3 are slower than
the strcspn main loop for large strings (though reject length 2-4 could be
special cased in the future to gain even more performance).

Tested on x86_64, i686, and aarch64.

	* string/Version (libc): Add GLIBC_2.24.
	* string/strcspn.c (strcspn): Rewrite function.
	* string/bits/string2.h (strcspn): Use __builtin_strcspn.
	(__strcspn_c1): Remove inline function.
	(__strcspn_c2): Likewise.
	(__strcspn_c3): Likewise.
	* string/string-inline.c
	[SHLIB_COMPAT(libc, GLIBC_2_1_1, GLIBC_2_24)] (__strcspn_c1): Add
	compatibility symbol.
	[SHLIB_COMPAT(libc, GLIBC_2_1_1, GLIBC_2_24)] (__strcspn_c2):
	Likewise.
	[SHLIB_COMPAT(libc, GLIBC_2_1_1, GLIBC_2_24)] (__strcspn_c3):
	Likewise.
	* sysdeps/i386/string-inlines.c: Include generic string-inlines.c.
This commit is contained in:
Wilco Dijkstra
2016-03-25 16:44:26 -03:00
committed by Adhemerval Zanella
parent d8a012c5c9
commit d3496c9f4f
6 changed files with 102 additions and 96 deletions
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46
string/strcspn.c
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@ -16,6 +16,7 @@
<http://www.gnu.org/licenses/>. */
#include <string.h>
#include <stdint.h>
#undef strcspn
@ -26,16 +27,45 @@
/* Return the length of the maximum initial segment of S
which contains no characters from REJECT. */
size_t
STRCSPN (const char *s, const char *reject)
STRCSPN (const char *str, const char *reject)
{
size_t count = 0;
if (__glibc_unlikely (reject[0] == '\0') ||
__glibc_unlikely (reject[1] == '\0'))
return __strchrnul (str, reject [0]) - str;
while (*s != '\0')
if (strchr (reject, *s++) == NULL)
++count;
else
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);
return count;
unsigned char *s = (unsigned char*) reject;
unsigned char tmp;
do
p[tmp = *s++] = 1;
while (tmp);
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 + 1 : count - c2 + 3;
}
libc_hidden_builtin_def (strcspn)