1 /* c-strcasestr.c -- case insensitive substring search in C locale
2 Copyright (C) 2005-2007 Free Software Foundation, Inc.
3 Written by Bruno Haible <bruno@clisp.org>, 2005.
5 This program is free software: you can redistribute it and/or modify
6 it under the terms of the GNU General Public License as published by
7 the Free Software Foundation; either version 3 of the License, or
8 (at your option) any later version.
10 This program is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 GNU General Public License for more details.
15 You should have received a copy of the GNU General Public License
16 along with this program. If not, see <http://www.gnu.org/licenses/>. */
21 #include "c-strcasestr.h"
30 /* Knuth-Morris-Pratt algorithm.
31 See http://en.wikipedia.org/wiki/Knuth-Morris-Pratt_algorithm
32 Return a boolean indicating success. */
34 knuth_morris_pratt (const char *haystack, const char *needle,
37 size_t m = strlen (needle);
39 /* Allocate the table. */
40 size_t *table = (size_t *) malloca (m * sizeof (size_t));
45 0 < table[i] <= i is defined such that
46 rhaystack[0..i-1] == needle[0..i-1] and rhaystack[i] != needle[i]
48 forall 0 <= x < table[i]: rhaystack[x..x+m-1] != needle[0..m-1],
49 and table[i] is as large as possible with this property.
50 table[0] remains uninitialized. */
56 for (i = 2; i < m; i++)
58 unsigned char b = c_tolower ((unsigned char) needle[i - 1]);
62 if (b == c_tolower ((unsigned char) needle[j]))
77 /* Search, using the table to accelerate the processing. */
80 const char *rhaystack;
81 const char *phaystack;
87 /* Invariant: phaystack = rhaystack + j. */
88 while (*phaystack != '\0')
89 if (c_tolower ((unsigned char) needle[j])
90 == c_tolower ((unsigned char) *phaystack))
96 /* The entire needle has been found. */
103 /* Found a match of needle[0..j-1], mismatch at needle[j]. */
104 rhaystack += table[j];
109 /* Found a mismatch at needle[0] already. */
119 /* Find the first occurrence of NEEDLE in HAYSTACK, using case-insensitive
121 Note: This function may, in multibyte locales, return success even if
122 strlen (haystack) < strlen (needle) ! */
124 c_strcasestr (const char *haystack, const char *needle)
126 /* Be careful not to look at the entire extent of haystack or needle
127 until needed. This is useful because of these two cases:
128 - haystack may be very long, and a match of needle found early,
129 - needle may be very long, and not even a short initial segment of
130 needle may be found in haystack. */
133 /* Minimizing the worst-case complexity:
134 Let n = strlen(haystack), m = strlen(needle).
135 The naïve algorithm is O(n*m) worst-case.
136 The Knuth-Morris-Pratt algorithm is O(n) worst-case but it needs a
138 To achieve linear complexity and yet amortize the cost of the memory
139 allocation, we activate the Knuth-Morris-Pratt algorithm only once
140 the naïve algorithm has already run for some time; more precisely,
142 - the outer loop count is >= 10,
143 - the average number of comparisons per outer loop is >= 5,
144 - the total number of comparisons is >= m.
145 But we try it only once. If the memory allocation attempt failed,
146 we don't retry it. */
148 size_t outer_loop_count = 0;
149 size_t comparison_count = 0;
150 size_t last_ccount = 0; /* last comparison count */
151 const char *needle_last_ccount = needle; /* = needle + last_ccount */
153 /* Speed up the following searches of needle by caching its first
155 unsigned char b = c_tolower ((unsigned char) *needle);
160 if (*haystack == '\0')
164 /* See whether it's advisable to use an asymptotically faster
167 && outer_loop_count >= 10
168 && comparison_count >= 5 * outer_loop_count)
170 /* See if needle + comparison_count now reaches the end of
172 if (needle_last_ccount != NULL)
174 needle_last_ccount +=
175 strnlen (needle_last_ccount, comparison_count - last_ccount);
176 if (*needle_last_ccount == '\0')
177 needle_last_ccount = NULL;
178 last_ccount = comparison_count;
180 if (needle_last_ccount == NULL)
182 /* Try the Knuth-Morris-Pratt algorithm. */
185 knuth_morris_pratt (haystack, needle - 1, &result);
187 return (char *) result;
194 if (c_tolower ((unsigned char) *haystack) == b)
195 /* The first character matches. */
197 const char *rhaystack = haystack + 1;
198 const char *rneedle = needle;
200 for (;; rhaystack++, rneedle++)
202 if (*rneedle == '\0')
204 return (char *) haystack;
205 if (*rhaystack == '\0')
209 if (c_tolower ((unsigned char) *rhaystack)
210 != c_tolower ((unsigned char) *rneedle))
211 /* Nothing in this round. */
218 return (char *) haystack;