diff options
Diffstat (limited to 'string/strstr.c')
| -rw-r--r-- | string/strstr.c | 142 |
1 files changed, 53 insertions, 89 deletions
diff --git a/string/strstr.c b/string/strstr.c index fce1f2a756..a9dc312992 100644 --- a/string/strstr.c +++ b/string/strstr.c @@ -1,5 +1,5 @@ /* Return the offset of one string within another. - Copyright (C) 1994,1996,1997,2000,2001,2003 Free Software Foundation, Inc. + Copyright (C) 1994,1996,1997,2000,2001,2003,2008 Free Software Foundation, Inc. This file is part of the GNU C Library. The GNU C Library is free software; you can redistribute it and/or @@ -17,107 +17,71 @@ Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA. */ -/* - * My personal strstr() implementation that beats most other algorithms. - * Until someone tells me otherwise, I assume that this is the - * fastest implementation of strstr() in C. - * I deliberately chose not to comment it. You should have at least - * as much fun trying to understand it, as I had to write it :-). - * - * Stephen R. van den Berg, berg@pool.informatik.rwth-aachen.de */ +/* This particular implementation was written by Eric Blake, 2008. */ -#if HAVE_CONFIG_H +#ifndef _LIBC # include <config.h> #endif -#if defined _LIBC || defined HAVE_STRING_H -# include <string.h> +/* Specification of strstr. */ +#include <string.h> + +#include <stdbool.h> + +#ifndef _LIBC +# define __builtin_expect(expr, val) (expr) #endif -typedef unsigned chartype; +#define RETURN_TYPE char * +#define AVAILABLE(h, h_l, j, n_l) \ + (!memchr ((h) + (h_l), '\0', (j) + (n_l) - (h_l)) \ + && ((h_l) = (j) + (n_l))) +#include "str-two-way.h" #undef strstr +/* Return the first occurrence of NEEDLE in HAYSTACK. Return HAYSTACK + if NEEDLE is empty, otherwise NULL if NEEDLE is not found in + HAYSTACK. */ char * -strstr (phaystack, pneedle) - const char *phaystack; - const char *pneedle; +strstr (const char *haystack_start, const char *needle_start) { - const unsigned char *haystack, *needle; - chartype b; - const unsigned char *rneedle; - - haystack = (const unsigned char *) phaystack; + const char *haystack = haystack_start; + const char *needle = needle_start; + size_t needle_len; /* Length of NEEDLE. */ + size_t haystack_len; /* Known minimum length of HAYSTACK. */ + bool ok = true; /* True if NEEDLE is prefix of HAYSTACK. */ - if ((b = *(needle = (const unsigned char *) pneedle))) - { - chartype c; - haystack--; /* possible ANSI violation */ + /* Determine length of NEEDLE, and in the process, make sure + HAYSTACK is at least as long (no point processing all of a long + NEEDLE if HAYSTACK is too short). */ + while (*haystack && *needle) + ok &= *haystack++ == *needle++; + if (*needle) + return NULL; + if (ok) + return (char *) haystack_start; - { - chartype a; - do - if (!(a = *++haystack)) - goto ret0; - while (a != b); - } + /* Reduce the size of haystack using strchr, since it has a smaller + linear coefficient than the Two-Way algorithm. */ + needle_len = needle - needle_start; + haystack = strchr (haystack_start + 1, *needle_start); + if (!haystack || __builtin_expect (needle_len == 1, 0)) + return (char *) haystack; + needle -= needle_len; + haystack_len = (haystack > haystack_start + needle_len ? 1 + : needle_len + haystack_start - haystack); - if (!(c = *++needle)) - goto foundneedle; - ++needle; - goto jin; - - for (;;) - { - { - chartype a; - if (0) - jin:{ - if ((a = *++haystack) == c) - goto crest; - } - else - a = *++haystack; - do - { - for (; a != b; a = *++haystack) - { - if (!a) - goto ret0; - if ((a = *++haystack) == b) - break; - if (!a) - goto ret0; - } - } - while ((a = *++haystack) != c); - } - crest: - { - chartype a; - { - const unsigned char *rhaystack; - if (*(rhaystack = haystack-- + 1) == (a = *(rneedle = needle))) - do - { - if (!a) - goto foundneedle; - if (*++rhaystack != (a = *++needle)) - break; - if (!a) - goto foundneedle; - } - while (*++rhaystack == (a = *++needle)); - needle = rneedle; /* took the register-poor aproach */ - } - if (!a) - break; - } - } - } -foundneedle: - return (char *) haystack; -ret0: - return 0; + /* Perform the search. Abstract memory is considered to be an array + of 'unsigned char' values, not an array of 'char' values. See + ISO C 99 section 6.2.6.1. */ + if (needle_len < LONG_NEEDLE_THRESHOLD) + return two_way_short_needle ((const unsigned char *) haystack, + haystack_len, + (const unsigned char *) needle, needle_len); + return two_way_long_needle ((const unsigned char *) haystack, haystack_len, + (const unsigned char *) needle, needle_len); } libc_hidden_builtin_def (strstr) + +#undef LONG_NEEDLE_THRESHOLD |