1 /* c-strcasestr.c -- case insensitive substring search in C locale
2 Copyright (C) 2005-2006 Free Software Foundation, Inc.
3 Written by Bruno Haible <bruno@clisp.org>, 2005.
4
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 2, or (at your option)
8 any later version.
9
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.
14
15 You should have received a copy of the GNU General Public License
16 along with this program; if not, write to the Free Software Foundation,
17 Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */
18
19 #include <config.h>
20
21 /* Specification. */
22 #include "c-strcasestr.h"
23
24 #include <stddef.h>
25
26 #include "c-ctype.h"
27
28 /* Find the first occurrence of NEEDLE in HAYSTACK, using case-insensitive
29 comparison.
30 Note: This function may, in multibyte locales, return success even if
31 strlen (haystack) < strlen (needle) ! */
32 char *
c_strcasestr(const char * haystack,const char * needle)33 c_strcasestr (const char *haystack, const char *needle)
34 {
35 /* Be careful not to look at the entire extent of haystack or needle
36 until needed. This is useful because of these two cases:
37 - haystack may be very long, and a match of needle found early,
38 - needle may be very long, and not even a short initial segment of
39 needle may be found in haystack. */
40 if (*needle != '\0')
41 {
42 /* Speed up the following searches of needle by caching its first
43 character. */
44 unsigned char b = c_tolower ((unsigned char) *needle);
45
46 needle++;
47 for (;; haystack++)
48 {
49 if (*haystack == '\0')
50 /* No match. */
51 return NULL;
52 if (c_tolower ((unsigned char) *haystack) == b)
53 /* The first character matches. */
54 {
55 const char *rhaystack = haystack + 1;
56 const char *rneedle = needle;
57
58 for (;; rhaystack++, rneedle++)
59 {
60 if (*rneedle == '\0')
61 /* Found a match. */
62 return (char *) haystack;
63 if (*rhaystack == '\0')
64 /* No match. */
65 return NULL;
66 if (c_tolower ((unsigned char) *rhaystack)
67 != c_tolower ((unsigned char) *rneedle))
68 /* Nothing in this round. */
69 break;
70 }
71 }
72 }
73 }
74 else
75 return (char *) haystack;
76 }
77