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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>
94 lines
3.2 KiB
C
94 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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/* 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 strstr. */
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#include <string.h>
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#include <stdbool.h>
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#ifndef _LIBC
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# define __builtin_expect(expr, val) (expr)
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#endif
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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 FASTSEARCH(S,C,N) (void*) strchr ((void*)(S), (C))
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#include "str-two-way.h"
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#undef strstr
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#ifndef STRSTR
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#define STRSTR strstr
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#endif
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/* Return the first occurrence of NEEDLE in HAYSTACK. Return HAYSTACK
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if NEEDLE is empty, otherwise NULL if NEEDLE is not found in
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HAYSTACK. */
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char *
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STRSTR (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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ok &= *haystack++ == *needle++;
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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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/* Reduce the size of haystack using strchr, since it has a smaller
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linear coefficient than the Two-Way algorithm. */
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needle_len = needle - needle_start;
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haystack = strchr (haystack_start + 1, *needle_start);
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if (!haystack || __builtin_expect (needle_len == 1, 0))
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return (char *) haystack;
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needle -= needle_len;
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haystack_len = (haystack > haystack_start + needle_len ? 1
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: needle_len + haystack_start - haystack);
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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, 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, needle_len);
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}
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libc_hidden_builtin_def (strstr)
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#undef LONG_NEEDLE_THRESHOLD
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