X-Git-Url: http://erislabs.net/gitweb/?a=blobdiff_plain;ds=sidebyside;f=lib%2Fc-strstr.c;h=e225128802f82848bad8a80ad433cad35e4c88ef;hb=25fb29a19d9993a32075b7c3fefa959e3345ab64;hp=fe38f5321955150abbd597d85951179b3c1b9878;hpb=867ac64402c080a66aef20afb87faec26394cd43;p=gnulib.git diff --git a/lib/c-strstr.c b/lib/c-strstr.c index fe38f5321..e22512880 100644 --- a/lib/c-strstr.c +++ b/lib/c-strstr.c @@ -1,11 +1,11 @@ /* c-strstr.c -- substring search in C locale - Copyright (C) 2005-2007 Free Software Foundation, Inc. + Copyright (C) 2005-2013 Free Software Foundation, Inc. Written by Bruno Haible , 2005, 2007. - This program is free software; you can redistribute it and/or modify + This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by - the Free Software Foundation; either version 2, or (at your option) - any later version. + the Free Software Foundation; either version 3 of the License, or + (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of @@ -13,200 +13,20 @@ GNU General Public License for more details. You should have received a copy of the GNU General Public License - along with this program; if not, write to the Free Software Foundation, - Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ + along with this program. If not, see . */ #include /* Specification. */ #include "c-strstr.h" -#include -#include #include -/* Knuth-Morris-Pratt algorithm. - See http://en.wikipedia.org/wiki/Knuth-Morris-Pratt_algorithm - Return a boolean indicating success. */ -static bool -knuth_morris_pratt (const char *haystack, const char *needle, - const char **resultp) -{ - size_t m = strlen (needle); - - /* Allocate the table. */ - size_t *table = (size_t *) malloc (m * sizeof (size_t)); - if (table == NULL) - return false; - /* Fill the table. - For 0 < i < m: - 0 < table[i] <= i is defined such that - rhaystack[0..i-1] == needle[0..i-1] and rhaystack[i] != needle[i] - implies - forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1], - and table[i] is as large as possible with this property. - table[0] remains uninitialized. */ - { - size_t i, j; - - table[1] = 1; - j = 0; - for (i = 2; i < m; i++) - { - unsigned char b = (unsigned char) needle[i - 1]; - - for (;;) - { - if (b == (unsigned char) needle[j]) - { - table[i] = i - ++j; - break; - } - if (j == 0) - { - table[i] = i; - break; - } - j = j - table[j]; - } - } - } - - /* Search, using the table to accelerate the processing. */ - { - size_t j; - const char *rhaystack; - const char *phaystack; - - *resultp = NULL; - j = 0; - rhaystack = haystack; - phaystack = haystack; - /* Invariant: phaystack = rhaystack + j. */ - while (*phaystack != '\0') - if ((unsigned char) needle[j] == (unsigned char) *phaystack) - { - j++; - phaystack++; - if (j == m) - { - /* The entire needle has been found. */ - *resultp = rhaystack; - break; - } - } - else if (j > 0) - { - /* Found a match of needle[0..j-1], mismatch at needle[j]. */ - rhaystack += table[j]; - j -= table[j]; - } - else - { - /* Found a mismatch at needle[0] already. */ - rhaystack++; - phaystack++; - } - } - - free (table); - return true; -} - /* Find the first occurrence of NEEDLE in HAYSTACK. */ char * c_strstr (const char *haystack, const char *needle) { - /* Be careful not to look at the entire extent of haystack or needle - until needed. This is useful because of these two cases: - - haystack may be very long, and a match of needle found early, - - needle may be very long, and not even a short initial segment of - needle may be found in haystack. */ - if (*needle != '\0') - { - /* Minimizing the worst-case complexity: - Let n = strlen(haystack), m = strlen(needle). - The naïve algorithm is O(n*m) worst-case. - The Knuth-Morris-Pratt algorithm is O(n) worst-case but it needs a - memory allocation. - To achieve linear complexity and yet amortize the cost of the memory - allocation, we activate the Knuth-Morris-Pratt algorithm only once - the naïve algorithm has already run for some time; more precisely, - when - - the outer loop count is >= 10, - - the average number of comparisons per outer loop is >= 5, - - the total number of comparisons is >= m. - But we try it only once. If the memory allocation attempt failed, - we don't retry it. */ - bool try_kmp = true; - size_t outer_loop_count = 0; - size_t comparison_count = 0; - size_t last_ccount = 0; /* last comparison count */ - const char *needle_last_ccount = needle; /* = needle + last_ccount */ - - /* Speed up the following searches of needle by caching its first - character. */ - unsigned char b = (unsigned char) *needle; - - needle++; - for (;; haystack++) - { - if (*haystack == '\0') - /* No match. */ - return NULL; - - /* See whether it's advisable to use an asymptotically faster - algorithm. */ - if (try_kmp - && outer_loop_count >= 10 - && comparison_count >= 5 * outer_loop_count) - { - /* See if needle + comparison_count now reaches the end of - needle. */ - if (needle_last_ccount != NULL) - { - needle_last_ccount += - strnlen (needle_last_ccount, comparison_count - last_ccount); - if (*needle_last_ccount == '\0') - needle_last_ccount = NULL; - last_ccount = comparison_count; - } - if (needle_last_ccount == NULL) - { - /* Try the Knuth-Morris-Pratt algorithm. */ - const char *result; - bool success = - knuth_morris_pratt (haystack, needle - 1, &result); - if (success) - return (char *) result; - try_kmp = false; - } - } - - outer_loop_count++; - comparison_count++; - if ((unsigned char) *haystack == b) - /* The first character matches. */ - { - const char *rhaystack = haystack + 1; - const char *rneedle = needle; - - for (;; rhaystack++, rneedle++) - { - if (*rneedle == '\0') - /* Found a match. */ - return (char *) haystack; - if (*rhaystack == '\0') - /* No match. */ - return NULL; - comparison_count++; - if ((unsigned char) *rhaystack != (unsigned char) *rneedle) - /* Nothing in this round. */ - break; - } - } - } - } - else - return (char *) haystack; + /* POSIX says that strstr() interprets the strings as byte sequences, not + as character sequences in the current locale. */ + return strstr (haystack, needle); }