libc: Use musl's O(n) memmem and strstr
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
parent
c11bbc7dab
commit
88521634e9
Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=315467
@ -26,7 +26,7 @@
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.\"
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.\" $FreeBSD$
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.\"
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.Dd May 26, 2015
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.Dd March 17, 2017
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.Dt MEMMEM 3
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.Os
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.Sh NAME
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@ -77,8 +77,11 @@ The
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.Fn memmem
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function first appeared in
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.Fx 6.0 .
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.Sh AUTHORS
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It was replaced with an optimized O(n) implementation from the musl libc
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project in
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.Fx 12.0 .
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.An Pascal Gloor Aq Mt pascal.gloor@spale.com
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provided this man page along with the previous implementation.
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.Sh BUGS
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This function was broken in Linux libc up to and including version 5.0.9
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and in GNU libc prior to version 2.1.
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@ -1,65 +1,173 @@
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/*-
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* Copyright (c) 2005 Pascal Gloor <pascal.gloor@spale.com>
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* Copyright (c) 2005-2014 Rich Felker, et al.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
|
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
|
||||
* notice, this list of conditions and the following disclaimer in the
|
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* documentation and/or other materials provided with the distribution.
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* 3. The name of the author may not be used to endorse or promote
|
||||
* products derived from this software without specific prior written
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* permission.
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* Permission is hereby granted, free of charge, to any person obtaining
|
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* a copy of this software and associated documentation files (the
|
||||
* "Software"), to deal in the Software without restriction, including
|
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* without limitation the rights to use, copy, modify, merge, publish,
|
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* distribute, sublicense, and/or sell copies of the Software, and to
|
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* permit persons to whom the Software is furnished to do so, subject to
|
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* the following conditions:
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
||||
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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* The above copyright notice and this permission notice shall be
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* included in all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
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* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
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* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
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* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <string.h>
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#include <stdint.h>
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/*
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* Find the first occurrence of the byte string s in byte string l.
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*/
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void *
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memmem(const void *l, size_t l_len, const void *s, size_t s_len)
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static char *twobyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
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{
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register char *cur, *last;
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const char *cl = (const char *)l;
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const char *cs = (const char *)s;
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/* empty "s" matches the beginning of "l" */
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if (s_len == 0)
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return (void *)cl;
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/* "s" must be smaller or equal to "l" */
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if (l_len < s_len)
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return NULL;
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/* special case where s_len == 1 */
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if (s_len == 1)
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return memchr(l, (int)*cs, l_len);
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/* the last position where its possible to find "s" in "l" */
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last = (char *)cl + l_len - s_len;
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for (cur = (char *)cl; cur <= last; cur++)
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if (cur[0] == cs[0] && memcmp(cur, cs, s_len) == 0)
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return cur;
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return NULL;
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uint16_t nw = n[0]<<8 | n[1], hw = h[0]<<8 | h[1];
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for (h++, k--; k; k--, hw = hw<<8 | *++h)
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if (hw == nw) return (char *)h-1;
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return 0;
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}
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static char *threebyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
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{
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uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8;
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uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8;
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for (h+=2, k-=2; k; k--, hw = (hw|*++h)<<8)
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if (hw == nw) return (char *)h-2;
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return 0;
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}
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static char *fourbyte_memmem(const unsigned char *h, size_t k, const unsigned char *n)
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{
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uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3];
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uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3];
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for (h+=3, k-=3; k; k--, hw = hw<<8 | *++h)
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if (hw == nw) return (char *)h-3;
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return 0;
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}
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#define MAX(a,b) ((a)>(b)?(a):(b))
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#define MIN(a,b) ((a)<(b)?(a):(b))
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#define BITOP(a,b,op) \
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((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))
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static char *twoway_memmem(const unsigned char *h, const unsigned char *z, const unsigned char *n, size_t l)
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{
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size_t i, ip, jp, k, p, ms, p0, mem, mem0;
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size_t byteset[32 / sizeof(size_t)] = { 0 };
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size_t shift[256];
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/* Computing length of needle and fill shift table */
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for (i=0; i<l; i++)
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BITOP(byteset, n[i], |=), shift[n[i]] = i+1;
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/* Compute maximal suffix */
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ip = -1; jp = 0; k = p = 1;
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while (jp+k<l) {
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if (n[ip+k] == n[jp+k]) {
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if (k == p) {
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jp += p;
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k = 1;
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} else k++;
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} else if (n[ip+k] > n[jp+k]) {
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jp += k;
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k = 1;
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p = jp - ip;
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} else {
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ip = jp++;
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k = p = 1;
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}
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}
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ms = ip;
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p0 = p;
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/* And with the opposite comparison */
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ip = -1; jp = 0; k = p = 1;
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while (jp+k<l) {
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if (n[ip+k] == n[jp+k]) {
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if (k == p) {
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jp += p;
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k = 1;
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} else k++;
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} else if (n[ip+k] < n[jp+k]) {
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jp += k;
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k = 1;
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p = jp - ip;
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} else {
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ip = jp++;
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k = p = 1;
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}
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}
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if (ip+1 > ms+1) ms = ip;
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else p = p0;
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/* Periodic needle? */
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if (memcmp(n, n+p, ms+1)) {
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mem0 = 0;
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p = MAX(ms, l-ms-1) + 1;
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} else mem0 = l-p;
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mem = 0;
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/* Search loop */
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for (;;) {
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/* If remainder of haystack is shorter than needle, done */
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if (z-h < l) return 0;
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/* Check last byte first; advance by shift on mismatch */
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if (BITOP(byteset, h[l-1], &)) {
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k = l-shift[h[l-1]];
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if (k) {
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if (mem0 && mem && k < p) k = l-p;
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h += k;
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mem = 0;
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continue;
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}
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} else {
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h += l;
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mem = 0;
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continue;
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}
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/* Compare right half */
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for (k=MAX(ms+1,mem); k<l && n[k] == h[k]; k++);
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if (k < l) {
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h += k-ms;
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mem = 0;
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continue;
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}
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/* Compare left half */
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for (k=ms+1; k>mem && n[k-1] == h[k-1]; k--);
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if (k <= mem) return (char *)h;
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h += p;
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mem = mem0;
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}
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}
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void *memmem(const void *h0, size_t k, const void *n0, size_t l)
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{
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const unsigned char *h = h0, *n = n0;
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/* Return immediately on empty needle */
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if (!l) return (void *)h;
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/* Return immediately when needle is longer than haystack */
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if (k<l) return 0;
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/* Use faster algorithms for short needles */
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h = memchr(h0, *n, k);
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if (!h || l==1) return (void *)h;
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k -= h - (const unsigned char *)h0;
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if (k<l) return 0;
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if (l==2) return twobyte_memmem(h, k, n);
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if (l==3) return threebyte_memmem(h, k, n);
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if (l==4) return fourbyte_memmem(h, k, n);
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return twoway_memmem(h, h+k, n, l);
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}
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@ -1,61 +1,180 @@
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/*-
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* Copyright (c) 1990, 1993
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* The Regents of the University of California. All rights reserved.
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* Copyright (c) 2005-2014 Rich Felker, et al.
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*
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* This code is derived from software contributed to Berkeley by
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* Chris Torek.
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* Permission is hereby granted, free of charge, to any person obtaining
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* a copy of this software and associated documentation files (the
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* "Software"), to deal in the Software without restriction, including
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* without limitation the rights to use, copy, modify, merge, publish,
|
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* distribute, sublicense, and/or sell copies of the Software, and to
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* permit persons to whom the Software is furnished to do so, subject to
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* the following conditions:
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
|
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
|
||||
* notice, this list of conditions and the following disclaimer in the
|
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* documentation and/or other materials provided with the distribution.
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* 3. Neither the name of the University nor the names of its contributors
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* may be used to endorse or promote products derived from this software
|
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* without specific prior written permission.
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* The above copyright notice and this permission notice shall be
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* included in all copies or substantial portions of the Software.
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*
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* THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
|
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
|
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
|
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
|
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
|
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
|
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* SUCH DAMAGE.
|
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
|
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* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
|
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* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
|
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* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
|
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* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
|
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* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
|
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* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*/
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#if defined(LIBC_SCCS) && !defined(lint)
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static char sccsid[] = "@(#)strstr.c 8.1 (Berkeley) 6/4/93";
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#endif /* LIBC_SCCS and not lint */
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <string.h>
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#include <stdint.h>
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/*
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* Find the first occurrence of find in s.
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*/
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char *
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strstr(const char *s, const char *find)
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static char *twobyte_strstr(const unsigned char *h, const unsigned char *n)
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{
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char c, sc;
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size_t len;
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if ((c = *find++) != '\0') {
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len = strlen(find);
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do {
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do {
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if ((sc = *s++) == '\0')
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return (NULL);
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} while (sc != c);
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} while (strncmp(s, find, len) != 0);
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s--;
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}
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return ((char *)s);
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uint16_t nw = n[0]<<8 | n[1], hw = h[0]<<8 | h[1];
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for (h++; *h && hw != nw; hw = hw<<8 | *++h);
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return *h ? (char *)h-1 : 0;
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}
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static char *threebyte_strstr(const unsigned char *h, const unsigned char *n)
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{
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uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8;
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uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8;
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for (h+=2; *h && hw != nw; hw = (hw|*++h)<<8);
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return *h ? (char *)h-2 : 0;
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}
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static char *fourbyte_strstr(const unsigned char *h, const unsigned char *n)
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{
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uint32_t nw = n[0]<<24 | n[1]<<16 | n[2]<<8 | n[3];
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uint32_t hw = h[0]<<24 | h[1]<<16 | h[2]<<8 | h[3];
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for (h+=3; *h && hw != nw; hw = hw<<8 | *++h);
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return *h ? (char *)h-3 : 0;
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}
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#define MAX(a,b) ((a)>(b)?(a):(b))
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#define MIN(a,b) ((a)<(b)?(a):(b))
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#define BITOP(a,b,op) \
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((a)[(size_t)(b)/(8*sizeof *(a))] op (size_t)1<<((size_t)(b)%(8*sizeof *(a))))
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static char *twoway_strstr(const unsigned char *h, const unsigned char *n)
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{
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const unsigned char *z;
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size_t l, ip, jp, k, p, ms, p0, mem, mem0;
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size_t byteset[32 / sizeof(size_t)] = { 0 };
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size_t shift[256];
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/* Computing length of needle and fill shift table */
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for (l=0; n[l] && h[l]; l++)
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BITOP(byteset, n[l], |=), shift[n[l]] = l+1;
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if (n[l]) return 0; /* hit the end of h */
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/* Compute maximal suffix */
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ip = -1; jp = 0; k = p = 1;
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while (jp+k<l) {
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if (n[ip+k] == n[jp+k]) {
|
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if (k == p) {
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jp += p;
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k = 1;
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} else k++;
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} else if (n[ip+k] > n[jp+k]) {
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jp += k;
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k = 1;
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p = jp - ip;
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} else {
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ip = jp++;
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k = p = 1;
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}
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}
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ms = ip;
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p0 = p;
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/* And with the opposite comparison */
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ip = -1; jp = 0; k = p = 1;
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while (jp+k<l) {
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if (n[ip+k] == n[jp+k]) {
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if (k == p) {
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jp += p;
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k = 1;
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} else k++;
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} else if (n[ip+k] < n[jp+k]) {
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jp += k;
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k = 1;
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p = jp - ip;
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} else {
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ip = jp++;
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k = p = 1;
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}
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}
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if (ip+1 > ms+1) ms = ip;
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else p = p0;
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/* Periodic needle? */
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if (memcmp(n, n+p, ms+1)) {
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mem0 = 0;
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p = MAX(ms, l-ms-1) + 1;
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} else mem0 = l-p;
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mem = 0;
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/* Initialize incremental end-of-haystack pointer */
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z = h;
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/* Search loop */
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for (;;) {
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/* Update incremental end-of-haystack pointer */
|
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if (z-h < l) {
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/* Fast estimate for MIN(l,63) */
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size_t grow = l | 63;
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const unsigned char *z2 = memchr(z, 0, grow);
|
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if (z2) {
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z = z2;
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if (z-h < l) return 0;
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} else z += grow;
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}
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|
||||
/* 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);
|
||||
}
|
||||
|
||||
Loading…
Reference in New Issue
Block a user