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* string/Makefile (distribute): Add str-two-way.h.
2008-03-29 Eric Blake <ebb9@byu.net> Rewrite string searches to O(n) rather than O(n^2). * string/str-two-way.h: New file. For linear fixed-allocation string searching. * string/memmem.c: New implementation. * string/strstr.c: New implementation. * string/strcasestr.c: New implementation. * sysdeps/posix/getaddrinfo.c (getaddrinfo): Call _res_hconf_init
This commit is contained in:
Ulrich Drepper
142
string/strstr.c
142
string/strstr.c
@ -1,5 +1,5 @@
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/* Return the offset of one string within another.
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Copyright (C) 1994,1996,1997,2000,2001,2003 Free Software Foundation, Inc.
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Copyright (C) 1994,1996,1997,2000,2001,2003,2008 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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@ -17,107 +17,71 @@
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Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
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02111-1307 USA. */
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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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/* This particular implementation was written by Eric Blake, 2008. */
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#if HAVE_CONFIG_H
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#ifndef _LIBC
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# include <config.h>
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#endif
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#if defined _LIBC || defined HAVE_STRING_H
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# include <string.h>
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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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typedef unsigned chartype;
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#define RETURN_TYPE char *
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#define AVAILABLE(h, h_l, j, n_l) \
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(!memchr ((h) + (h_l), '\0', (j) + (n_l) - (h_l)) \
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&& ((h_l) = (j) + (n_l)))
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#include "str-two-way.h"
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#undef strstr
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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 (phaystack, pneedle)
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const char *phaystack;
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const char *pneedle;
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strstr (const char *haystack_start, const char *needle_start)
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{
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const unsigned char *haystack, *needle;
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chartype b;
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const unsigned char *rneedle;
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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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haystack = (const unsigned char *) phaystack;
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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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if ((b = *(needle = (const unsigned char *) pneedle)))
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{
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chartype c;
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haystack--; /* possible ANSI violation */
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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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{
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chartype a;
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do
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if (!(a = *++haystack))
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goto ret0;
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while (a != b);
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}
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if (!(c = *++needle))
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goto foundneedle;
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++needle;
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goto jin;
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for (;;)
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{
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{
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chartype a;
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if (0)
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jin:{
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if ((a = *++haystack) == c)
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goto crest;
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}
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else
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a = *++haystack;
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do
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{
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for (; a != b; a = *++haystack)
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{
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if (!a)
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goto ret0;
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if ((a = *++haystack) == b)
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break;
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if (!a)
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goto ret0;
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}
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}
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while ((a = *++haystack) != c);
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}
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crest:
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{
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chartype a;
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{
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const unsigned char *rhaystack;
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if (*(rhaystack = haystack-- + 1) == (a = *(rneedle = needle)))
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do
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{
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if (!a)
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goto foundneedle;
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if (*++rhaystack != (a = *++needle))
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break;
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if (!a)
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goto foundneedle;
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}
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while (*++rhaystack == (a = *++needle));
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needle = rneedle; /* took the register-poor aproach */
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}
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if (!a)
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break;
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}
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}
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}
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foundneedle:
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return (char *) haystack;
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ret0:
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return 0;
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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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