/* c-strstr.c -- substring search in C locale
- Copyright (C) 2005-2007 Free Software Foundation, Inc.
+ Copyright (C) 2005-2014 Free Software Foundation, Inc.
Written by Bruno Haible <bruno@clisp.org>, 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
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 <http://www.gnu.org/licenses/>. */
#include <config.h>
/* Specification. */
#include "c-strstr.h"
-#include <stdbool.h>
-#include <stdlib.h>
#include <string.h>
-/* 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);
}
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