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libc: Use musl's O(n) memmem and strstr

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It is O(n) in the length of the haystack (big) string, and has special
cases for short needle (little) strings, of one to four bytes, to avoid
excessive overhead.

There are a small set of nearly trivial cases where the startup overhead
of the musl implementation makes it slightly slower -- for example, a 31
byte needle that matches the beginning of the haystack.  It's faster for
non-trivial cases, and significantly so for inputs that trigger worst-
case behaviour of the previous implementation.  As an example, in my
tests a 16K needle that matches the end of a 64K haystack is nearly
2000x faster with this implementation.

Reviewed by:	bapt (earlier), ed (earlier)
Obtained from:	musl (snapshot at commit c718f9fc)
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D2601
This commit is contained in:
Ed Maste 2017-03-18 00:51:39 +00:00
parent c11bbc7dab
commit 88521634e9
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=315467
3 changed files with 335 additions and 105 deletions
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7
lib/libc/string/memmem.3
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@ -26,7 +26,7 @@
.\" .\"
.\" $FreeBSD$ .\" $FreeBSD$
.\" .\"
.Dd May 26, 2015 .Dd March 17, 2017
.Dt MEMMEM 3 .Dt MEMMEM 3
.Os .Os
.Sh NAME .Sh NAME
@ -77,8 +77,11 @@ The
.Fn memmem .Fn memmem
function first appeared in function first appeared in
.Fx 6.0 . .Fx 6.0 .
.Sh AUTHORS It was replaced with an optimized O(n) implementation from the musl libc
project in
.Fx 12.0 .
.An Pascal Gloor Aq Mt pascal.gloor@spale.com .An Pascal Gloor Aq Mt pascal.gloor@spale.com
provided this man page along with the previous implementation.
.Sh BUGS .Sh BUGS
This function was broken in Linux libc up to and including version 5.0.9 This function was broken in Linux libc up to and including version 5.0.9
and in GNU libc prior to version 2.1. and in GNU libc prior to version 2.1.

216
lib/libc/string/memmem.c
View File

@ -1,65 +1,173 @@
/*- /*-
* Copyright (c) 2005 Pascal Gloor <pascal.gloor@spale.com> * Copyright (c) 2005-2014 Rich Felker, et al.
* *
* Redistribution and use in source and binary forms, with or without * Permission is hereby granted, free of charge, to any person obtaining
* modification, are permitted provided that the following conditions * a copy of this software and associated documentation files (the
* are met: * "Software"), to deal in the Software without restriction, including
* 1. Redistributions of source code must retain the above copyright * without limitation the rights to use, copy, modify, merge, publish,
* notice, this list of conditions and the following disclaimer. * distribute, sublicense, and/or sell copies of the Software, and to
* 2. Redistributions in binary form must reproduce the above copyright * permit persons to whom the Software is furnished to do so, subject to
* notice, this list of conditions and the following disclaimer in the * the following conditions:
* documentation and/or other materials provided with the distribution.
* 3. The name of the author may not be used to endorse or promote
* products derived from this software without specific prior written
* permission.
* *
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND * The above copyright notice and this permission notice shall be
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * included in all copies or substantial portions of the Software.
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE *
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
* SUCH DAMAGE.
*/ */
#include <sys/cdefs.h> #include <sys/cdefs.h>
__FBSDID("$FreeBSD$"); __FBSDID("$FreeBSD$");
#include <string.h> #include <string.h>
#include <stdint.h>
/* static char *twobyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
* Find the first occurrence of the byte string s in byte string l.
*/
void *
memmem(const void *l, size_t l_len, const void *s, size_t s_len)
{ {
register char *cur, *last; uint16_t nw = n[0]<<8 | n[1], hw = h[0]<<8 | h[1];
const char *cl = (const char *)l; for (h++, k--; k; k--, hw = hw<<8 | *++h)
const char *cs = (const char *)s; if (hw == nw) return (char *)h-1;
return 0;
/* empty "s" matches the beginning of "l" */ }
if (s_len == 0)
return (void *)cl; static char *threebyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
{
/* "s" must be smaller or equal to "l" */ uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8;
if (l_len < s_len) uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8;
return NULL; for (h+=2, k-=2; k; k--, hw = (hw|*++h)<<8)
if (hw == nw) return (char *)h-2;
/* special case where s_len == 1 */ return 0;
if (s_len == 1) }
return memchr(l, (int)*cs, l_len);
static char *fourbyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
/* the last position where its possible to find "s" in "l" */ {
last = (char *)cl + l_len - s_len; uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3];
uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3];
for (cur = (char *)cl; cur <= last; cur++) for (h+=3, k-=3; k; k--, hw = hw<<8 | *++h)
if (cur[0] == cs[0] && memcmp(cur, cs, s_len) == 0) if (hw == nw) return (char *)h-3;
return cur; return 0;
}
return NULL;
#define MAX(a,b) ((a)>(b)?(a):(b))
#define MIN(a,b) ((a)<(b)?(a):(b))
#define BITOP(a,b,op) \
((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))
static char *twoway_memmem(const unsigned char *h, const unsigned char *z, const unsigned char *n, size_t l)
{
size_t i, ip, jp, k, p, ms, p0, mem, mem0;
size_t byteset[32 / sizeof(size_t)] = { 0 };
size_t shift[256];
/* Computing length of needle and fill shift table */
for (i=0; i<l; i++)
BITOP(byteset, n[i], |=), shift[n[i]] = i+1;
/* Compute maximal suffix */
ip = -1; jp = 0; k = p = 1;
while (jp+k<l) {
if (n[ip+k] == n[jp+k]) {
if (k == p) {
jp += p;
k = 1;
} else k++;
} else if (n[ip+k] > n[jp+k]) {
jp += k;
k = 1;
p = jp - ip;
} else {
ip = jp++;
k = p = 1;
}
}
ms = ip;
p0 = p;
/* And with the opposite comparison */
ip = -1; jp = 0; k = p = 1;
while (jp+k<l) {
if (n[ip+k] == n[jp+k]) {
if (k == p) {
jp += p;
k = 1;
} else k++;
} else if (n[ip+k] < n[jp+k]) {
jp += k;
k = 1;
p = jp - ip;
} else {
ip = jp++;
k = p = 1;
}
}
if (ip+1 > ms+1) ms = ip;
else p = p0;
/* Periodic needle? */
if (memcmp(n, n+p, ms+1)) {
mem0 = 0;
p = MAX(ms, l-ms-1) + 1;
} else mem0 = l-p;
mem = 0;
/* Search loop */
for (;;) {
/* If remainder of haystack is shorter than needle, done */
if (z-h < l) return 0;
/* Check last byte first; advance by shift on mismatch */
if (BITOP(byteset, h[l-1], &)) {
k = l-shift[h[l-1]];
if (k) {
if (mem0 && mem && k < p) k = l-p;
h += k;
mem = 0;
continue;
}
} else {
h += l;
mem = 0;
continue;
}
/* Compare right half */
for (k=MAX(ms+1,mem); k<l && n[k] == h[k]; k++);
if (k < l) {
h += k-ms;
mem = 0;
continue;
}
/* Compare left half */
for (k=ms+1; k>mem && n[k-1] == h[k-1]; k--);
if (k <= mem) return (char *)h;
h += p;
mem = mem0;
}
}
void *memmem(const void *h0, size_t k, const void *n0, size_t l)
{
const unsigned char *h = h0, *n = n0;
/* Return immediately on empty needle */
if (!l) return (void *)h;
/* Return immediately when needle is longer than haystack */
if (k<l) return 0;
/* Use faster algorithms for short needles */
h = memchr(h0, *n, k);
if (!h || l==1) return (void *)h;
k -= h - (const unsigned char *)h0;
if (k<l) return 0;
if (l==2) return twobyte_memmem(h, k, n);
if (l==3) return threebyte_memmem(h, k, n);
if (l==4) return fourbyte_memmem(h, k, n);
return twoway_memmem(h, h+k, n, l);
} }

217
lib/libc/string/strstr.c
View File

@ -1,61 +1,180 @@
/*- /*-
* Copyright (c) 1990, 1993 * Copyright (c) 2005-2014 Rich Felker, et al.
* The Regents of the University of California. All rights reserved.
* *
* This code is derived from software contributed to Berkeley by * Permission is hereby granted, free of charge, to any person obtaining
* Chris Torek. * a copy of this software and associated documentation files (the
* "Software"), to deal in the Software without restriction, including
* without limitation the rights to use, copy, modify, merge, publish,
* distribute, sublicense, and/or sell copies of the Software, and to
* permit persons to whom the Software is furnished to do so, subject to
* the following conditions:
* *
* Redistribution and use in source and binary forms, with or without * The above copyright notice and this permission notice shall be
* modification, are permitted provided that the following conditions * included in all copies or substantial portions of the Software.
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the University nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
* *
* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*/ */
#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)strstr.c 8.1 (Berkeley) 6/4/93";
#endif /* LIBC_SCCS and not lint */
#include <sys/cdefs.h> #include <sys/cdefs.h>
__FBSDID("$FreeBSD$"); __FBSDID("$FreeBSD$");
#include <string.h> #include <string.h>
#include <stdint.h>
/* static char *twobyte_strstr(const unsigned char *h, const unsigned char *n)
* Find the first occurrence of find in s.
*/
char *
strstr(const char *s, const char *find)
{ {
char c, sc; uint16_t nw = n[0]<<8 | n[1], hw = h[0]<<8 | h[1];
size_t len; for (h++; *h && hw != nw; hw = hw<<8 | *++h);
return *h ? (char *)h-1 : 0;
if ((c = *find++) != '\0') { }
len = strlen(find);
do { static char *threebyte_strstr(const unsigned char *h, const unsigned char *n)
do { {
if ((sc = *s++) == '\0') uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8;
return (NULL); uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8;
} while (sc != c); for (h+=2; *h && hw != nw; hw = (hw|*++h)<<8);
} while (strncmp(s, find, len) != 0); return *h ? (char *)h-2 : 0;
s--; }
}
return ((char *)s); static char *fourbyte_strstr(const unsigned char *h, const unsigned char *n)
{
uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3];
uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3];
for (h+=3; *h && hw != nw; hw = hw<<8 | *++h);
return *h ? (char *)h-3 : 0;
}
#define MAX(a,b) ((a)>(b)?(a):(b))
#define MIN(a,b) ((a)<(b)?(a):(b))
#define BITOP(a,b,op) \
((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))
static char *twoway_strstr(const unsigned char *h, const unsigned char *n)
{
const unsigned char *z;
size_t l, ip, jp, k, p, ms, p0, mem, mem0;
size_t byteset[32 / sizeof(size_t)] = { 0 };
size_t shift[256];
/* Computing length of needle and fill shift table */
for (l=0; n[l] && h[l]; l++)
BITOP(byteset, n[l], |=), shift[n[l]] = l+1;
if (n[l]) return 0; /* hit the end of h */
/* Compute maximal suffix */
ip = -1; jp = 0; k = p = 1;
while (jp+k<l) {
if (n[ip+k] == n[jp+k]) {
if (k == p) {
jp += p;
k = 1;
} else k++;
} else if (n[ip+k] > n[jp+k]) {
jp += k;
k = 1;
p = jp - ip;
} else {
ip = jp++;
k = p = 1;
}
}
ms = ip;
p0 = p;
/* And with the opposite comparison */
ip = -1; jp = 0; k = p = 1;
while (jp+k<l) {
if (n[ip+k] == n[jp+k]) {
if (k == p) {
jp += p;
k = 1;
} else k++;
} else if (n[ip+k] < n[jp+k]) {
jp += k;
k = 1;
p = jp - ip;
} else {
ip = jp++;
k = p = 1;
}
}
if (ip+1 > ms+1) ms = ip;
else p = p0;
/* Periodic needle? */
if (memcmp(n, n+p, ms+1)) {
mem0 = 0;
p = MAX(ms, l-ms-1) + 1;
} else mem0 = l-p;
mem = 0;
/* Initialize incremental end-of-haystack pointer */
z = h;
/* Search loop */
for (;;) {
/* Update incremental end-of-haystack pointer */
if (z-h < l) {
/* Fast estimate for MIN(l,63) */
size_t grow = l | 63;
const unsigned char *z2 = memchr(z, 0, grow);
if (z2) {
z = z2;
if (z-h < l) return 0;
} else z += grow;
}
/* Check last byte first; advance by shift on mismatch */
if (BITOP(byteset, h[l-1], &)) {
k = l-shift[h[l-1]];
//printf("adv by %zu (on %c) at [%s] (%zu;l=%zu)\n", k, h[l-1], h, shift[h[l-1]], l);
if (k) {
if (mem0 && mem && k < p) k = l-p;
h += k;
mem = 0;
continue;
}
} else {
h += l;
mem = 0;
continue;
}
/* Compare right half */
for (k=MAX(ms+1,mem); n[k] && n[k] == h[k]; k++);
if (n[k]) {
h += k-ms;
mem = 0;
continue;
}
/* Compare left half */
for (k=ms+1; k>mem && n[k-1] == h[k-1]; k--);
if (k <= mem) return (char *)h;
h += p;
mem = mem0;
}
}
char *strstr(const char *h, const char *n)
{
/* Return immediately on empty needle */
if (!n[0]) return (char *)h;
/* Use faster algorithms for short needles */
h = strchr(h, *n);
if (!h || !n[1]) return (char *)h;
if (!h[1]) return 0;
if (!n[2]) return twobyte_strstr((void *)h, (void *)n);
if (!h[2]) return 0;
if (!n[3]) return threebyte_strstr((void *)h, (void *)n);
if (!h[3]) return 0;
if (!n[4]) return fourbyte_strstr((void *)h, (void *)n);
return twoway_strstr((void *)h, (void *)n);
} }