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3ae725dfb6
Improve strstr performance. Strstr tends to be slow because it uses
many calls to memchr and a slow byte loop to scan for the next match.
Performance is significantly improved by using strnlen on larger blocks
and using strchr to search for the next matching character. strcasestr
can also use strnlen to scan ahead, and memmem can use memchr to check
for the next match.
On the GLIBC bench tests the performance gains on Cortex-A72 are:
strstr: +25%
strcasestr: +4.3%
memmem: +18%
On a 256KB dataset strstr performance improves by 67%, strcasestr by 47%.
Reviewd-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
83 lines
2.9 KiB
C
83 lines
2.9 KiB
C
/* Copyright (C) 1991-2018 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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/* This particular implementation was written by Eric Blake, 2008. */
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#ifndef _LIBC
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# include <config.h>
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#endif
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/* Specification of memmem. */
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#include <string.h>
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#ifndef _LIBC
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# define __builtin_expect(expr, val) (expr)
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# define __memmem memmem
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#endif
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#define RETURN_TYPE void *
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#define AVAILABLE(h, h_l, j, n_l) ((j) <= (h_l) - (n_l))
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#define FASTSEARCH(S,C,N) (void*) memchr ((void *)(S), (C), (N))
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#include "str-two-way.h"
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#undef memmem
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/* Return the first occurrence of NEEDLE in HAYSTACK. Return HAYSTACK
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if NEEDLE_LEN is 0, otherwise NULL if NEEDLE is not found in
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HAYSTACK. */
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void *
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__memmem (const void *haystack_start, size_t haystack_len,
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const void *needle_start, size_t needle_len)
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{
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/* Abstract memory is considered to be an array of 'unsigned char' values,
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not an array of 'char' values. See ISO C 99 section 6.2.6.1. */
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const unsigned char *haystack = (const unsigned char *) haystack_start;
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const unsigned char *needle = (const unsigned char *) needle_start;
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if (needle_len == 0)
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/* The first occurrence of the empty string is deemed to occur at
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the beginning of the string. */
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return (void *) haystack;
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/* Sanity check, otherwise the loop might search through the whole
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memory. */
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if (__glibc_unlikely (haystack_len < needle_len))
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return NULL;
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/* Use optimizations in memchr when possible, to reduce the search
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size of haystack using a linear algorithm with a smaller
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coefficient. However, avoid memchr for long needles, since we
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can often achieve sublinear performance. */
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if (needle_len < LONG_NEEDLE_THRESHOLD)
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{
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haystack = memchr (haystack, *needle, haystack_len);
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if (!haystack || __builtin_expect (needle_len == 1, 0))
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return (void *) haystack;
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haystack_len -= haystack - (const unsigned char *) haystack_start;
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if (haystack_len < needle_len)
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return NULL;
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return two_way_short_needle (haystack, haystack_len, needle, needle_len);
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}
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else
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return two_way_long_needle (haystack, haystack_len, needle, needle_len);
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}
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libc_hidden_def (__memmem)
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weak_alias (__memmem, memmem)
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libc_hidden_weak (memmem)
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#undef LONG_NEEDLE_THRESHOLD
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