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1def6a34ae
Looking at the benchtests, both strstr and strcasestr spend a lot of time
in a slow initialization loop handling one character per iteration.
This can be simplified and use the much faster strlen/strnlen/strchr/memcmp.
Read ahead a few cachelines to reduce the number of strnlen calls, which
improves performance by ~3-4%. This patch improves the time taken for the
full strstr benchtest by >40%.
* string/strcasestr.c (STRCASESTR): Simplify and speedup first match.
* string/strstr.c (AVAILABLE): Likewise.
(cherry picked from commit 284f42bc77)
97 lines
3.2 KiB
C
97 lines
3.2 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)) \
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|| ((h_l) += __strnlen ((void*)((h) + (h_l)), (n_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, const char *needle)
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{
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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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/* Handle empty NEEDLE special case. */
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if (needle[0] == '\0')
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return (char *) haystack;
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/* Ensure HAYSTACK length is at least as long as NEEDLE length.
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Since a match may occur early on in a huge HAYSTACK, use strnlen
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and read ahead a few cachelines for improved performance. */
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needle_len = strlen (needle);
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haystack_len = __strnlen (haystack, needle_len + 256);
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if (haystack_len < needle_len)
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return NULL;
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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,
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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,
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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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