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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>
105 lines
3.4 KiB
C
105 lines
3.4 KiB
C
/* Return the offset of one string within another.
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Copyright (C) 1994-2018 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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/*
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* My personal strstr() implementation that beats most other algorithms.
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* Until someone tells me otherwise, I assume that this is the
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* fastest implementation of strstr() in C.
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* I deliberately chose not to comment it. You should have at least
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* as much fun trying to understand it, as I had to write it :-).
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*
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* Stephen R. van den Berg, berg@pool.informatik.rwth-aachen.de */
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/* Specification. */
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#include <string.h>
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#include <ctype.h>
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#include <stdbool.h>
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#include <strings.h>
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#define TOLOWER(Ch) tolower (Ch)
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/* Two-Way algorithm. */
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#define RETURN_TYPE char *
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#define AVAILABLE(h, h_l, j, n_l) \
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(((j) + (n_l) <= (h_l)) || ((h_l) += __strnlen ((void*)((h) + (h_l)), 512), \
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(j) + (n_l) <= (h_l)))
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#define CHECK_EOL (1)
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#define RET0_IF_0(a) if (!a) goto ret0
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#define CANON_ELEMENT(c) TOLOWER (c)
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#define CMP_FUNC(p1, p2, l) \
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__strncasecmp ((const char *) (p1), (const char *) (p2), l)
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#include "str-two-way.h"
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#undef strcasestr
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#undef __strcasestr
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#ifndef STRCASESTR
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#define STRCASESTR __strcasestr
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#endif
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/* Find the first occurrence of NEEDLE in HAYSTACK, using
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case-insensitive comparison. This function gives unspecified
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results in multibyte locales. */
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char *
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STRCASESTR (const char *haystack_start, const char *needle_start)
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{
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const char *haystack = haystack_start;
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const char *needle = needle_start;
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size_t needle_len; /* Length of NEEDLE. */
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size_t haystack_len; /* Known minimum length of HAYSTACK. */
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bool ok = true; /* True if NEEDLE is prefix of HAYSTACK. */
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/* Determine length of NEEDLE, and in the process, make sure
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HAYSTACK is at least as long (no point processing all of a long
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NEEDLE if HAYSTACK is too short). */
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while (*haystack && *needle)
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{
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ok &= (TOLOWER ((unsigned char) *haystack)
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== TOLOWER ((unsigned char) *needle));
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haystack++;
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needle++;
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}
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if (*needle)
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return NULL;
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if (ok)
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return (char *) haystack_start;
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needle_len = needle - needle_start;
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haystack = haystack_start + 1;
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haystack_len = needle_len - 1;
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/* Perform the search. Abstract memory is considered to be an array
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of 'unsigned char' values, not an array of 'char' values. See
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ISO C 99 section 6.2.6.1. */
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if (needle_len < LONG_NEEDLE_THRESHOLD)
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return two_way_short_needle ((const unsigned char *) haystack,
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haystack_len,
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(const unsigned char *) needle_start,
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needle_len);
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return two_way_long_needle ((const unsigned char *) haystack, haystack_len,
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(const unsigned char *) needle_start,
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needle_len);
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}
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#undef LONG_NEEDLE_THRESHOLD
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#ifndef NO_ALIAS
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weak_alias (__strcasestr, strcasestr)
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#endif
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