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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.
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Adhemerval Zanella committed Apr 1, 2016
1 parent d3496c9 commit 91f3b75
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16 changes: 16 additions & 0 deletions ChangeLog
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Original file line number Diff line number Diff line change
@@ -1,3 +1,19 @@
2016-04-01 Adhemerval Zanella <adhemerval.zanella@linaro.org>

* 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.
* string/string-inlines.c: Include generic version.

2016-04-01 Wilco Dijkstra <wdijkstr@arm.com>
Adhemerval Zanella <adhemerval.zanella@linaro.org>

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74 changes: 3 additions & 71 deletions string/bits/string2.h
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Original file line number Diff line number Diff line change
Expand Up @@ -914,78 +914,10 @@ __stpcpy_small (char *__dest,

/* Return the length of the initial segment of S which
consists entirely of characters in ACCEPT. */
#if !defined _HAVE_STRING_ARCH_strspn || defined _FORCE_INLINES
# ifndef _HAVE_STRING_ARCH_strspn
# if __GNUC_PREREQ (3, 2)
# define strspn(s, accept) \
__extension__ \
({ char __a0, __a1, __a2; \
(__builtin_constant_p (accept) && __string2_1bptr_p (accept) \
? ((__builtin_constant_p (s) && __string2_1bptr_p (s)) \
? __builtin_strspn (s, accept) \
: ((__a0 = ((const char *) (accept))[0], __a0 == '\0') \
? ((void) (s), (size_t) 0) \
: ((__a1 = ((const char *) (accept))[1], __a1 == '\0') \
? __strspn_c1 (s, __a0) \
: ((__a2 = ((const char *) (accept))[2], __a2 == '\0') \
? __strspn_c2 (s, __a0, __a1) \
: (((const char *) (accept))[3] == '\0' \
? __strspn_c3 (s, __a0, __a1, __a2) \
: __builtin_strspn (s, accept)))))) \
: __builtin_strspn (s, accept)); })
# else
# define strspn(s, accept) \
__extension__ \
({ char __a0, __a1, __a2; \
(__builtin_constant_p (accept) && __string2_1bptr_p (accept) \
? ((__a0 = ((const char *) (accept))[0], __a0 == '\0') \
? ((void) (s), (size_t) 0) \
: ((__a1 = ((const char *) (accept))[1], __a1 == '\0') \
? __strspn_c1 (s, __a0) \
: ((__a2 = ((const char *) (accept))[2], __a2 == '\0') \
? __strspn_c2 (s, __a0, __a1) \
: (((const char *) (accept))[3] == '\0' \
? __strspn_c3 (s, __a0, __a1, __a2) \
: strspn (s, accept))))) \
: strspn (s, accept)); })
# endif
#ifndef _HAVE_STRING_ARCH_strspn
# if __GNUC_PREREQ (3, 2)
# define strspn(s, accept) __builtin_strspn (s, accept)
# endif

__STRING_INLINE size_t __strspn_c1 (const char *__s, int __accept);
__STRING_INLINE size_t
__strspn_c1 (const char *__s, int __accept)
{
size_t __result = 0;
/* Please note that __accept never can be '\0'. */
while (__s[__result] == __accept)
++__result;
return __result;
}

__STRING_INLINE size_t __strspn_c2 (const char *__s, int __accept1,
int __accept2);
__STRING_INLINE size_t
__strspn_c2 (const char *__s, int __accept1, int __accept2)
{
size_t __result = 0;
/* Please note that __accept1 and __accept2 never can be '\0'. */
while (__s[__result] == __accept1 || __s[__result] == __accept2)
++__result;
return __result;
}

__STRING_INLINE size_t __strspn_c3 (const char *__s, int __accept1,
int __accept2, int __accept3);
__STRING_INLINE size_t
__strspn_c3 (const char *__s, int __accept1, int __accept2, int __accept3)
{
size_t __result = 0;
/* Please note that __accept1 to __accept3 never can be '\0'. */
while (__s[__result] == __accept1 || __s[__result] == __accept2
|| __s[__result] == __accept3)
++__result;
return __result;
}
#endif


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36 changes: 36 additions & 0 deletions string/string-inlines.c
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Original file line number Diff line number Diff line change
Expand Up @@ -71,4 +71,40 @@ __old_strcspn_c3 (const char *__s, int __reject1, int __reject2,
return __result;
}
compat_symbol (libc, __old_strcspn_c3, __strcspn_c3, GLIBC_2_1_1);

size_t
__old_strspn_c1 (const char *__s, int __accept)
{
size_t __result = 0;
/* Please note that __accept never can be '\0'. */
while (__s[__result] == __accept)
++__result;
return __result;
}
compat_symbol (libc, __old_strspn_c1, __strspn_c1, GLIBC_2_1_1);

size_t
__old_strspn_c2 (const char *__s, int __accept1, int __accept2)
{
size_t __result = 0;
/* Please note that __accept1 and __accept2 never can be '\0'. */
while (__s[__result] == __accept1 || __s[__result] == __accept2)
++__result;
return __result;
}
compat_symbol (libc, __old_strspn_c2, __strspn_c2, GLIBC_2_1_1);

size_t
__old_strspn_c3 (const char *__s, int __accept1, int __accept2,
int __accept3)
{
size_t __result = 0;
/* Please note that __accept1 to __accept3 never can be '\0'. */
while (__s[__result] == __accept1 || __s[__result] == __accept2
|| __s[__result] == __accept3)
++__result;
return __result;
}
compat_symbol (libc, __old_strspn_c3, __strspn_c3, GLIBC_2_1_1);

#endif
57 changes: 42 additions & 15 deletions string/strspn.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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)

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