lib/strcasestr.c

   1 /* Case-insensitive searching in a string.
   2    Copyright (C) 2005-2024 Free Software Foundation, Inc.
   3    Written by Bruno Haible <bruno@clisp.org>, 2005.
   4
   5    This file is free software: you can redistribute it and/or modify
   6    it under the terms of the GNU Lesser General Public License as
   7    published by the Free Software Foundation; either version 2.1 of the
   8    License, or (at your option) any later version.
   9
  10    This file 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 Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public License
  16    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  17
  18 #include <config.h>
  19
  20 /* Specification.  */
  21 #include <string.h>
  22
  23 #include <ctype.h>
  24 #include <strings.h>
  25
  26 /* Two-Way algorithm.  */
  27 #define RETURN_TYPE char *
  28 #define AVAILABLE(h, h_l, j, n_l)                       \
  29   (!memchr ((h) + (h_l), '\0', (j) + (n_l) - (h_l))     \
  30    && ((h_l) = (j) + (n_l)))
  31 #define CANON_ELEMENT(c) tolower (c)
  32 #define CMP_FUNC(p1, p2, l)                             \
  33   strncasecmp ((const char *) (p1), (const char *) (p2), l)
  34 #include "str-two-way.h"
  35
  36 /* Find the first occurrence of NEEDLE in HAYSTACK, using
  37    case-insensitive comparison.  This function gives unspecified
  38    results in multibyte locales.  */
  39 char *
  40 strcasestr (const char *haystack_start, const char *needle_start)
  41 {
  42   const char *haystack = haystack_start;
  43   const char *needle = needle_start;
  44   size_t needle_len; /* Length of NEEDLE.  */
  45   size_t haystack_len; /* Known minimum length of HAYSTACK.  */
  46   bool ok = true; /* True if NEEDLE is prefix of HAYSTACK.  */
  47
  48   /* Determine length of NEEDLE, and in the process, make sure
  49      HAYSTACK is at least as long (no point processing all of a long
  50      NEEDLE if HAYSTACK is too short).  */
  51   while (*haystack && *needle)
  52     {
  53       ok &= (tolower ((unsigned char) *haystack)
  54              == tolower ((unsigned char) *needle));
  55       haystack++;
  56       needle++;
  57     }
  58   if (*needle)
  59     return NULL;
  60   if (ok)
  61     return (char *) haystack_start;
  62   needle_len = needle - needle_start;
  63   haystack = haystack_start + 1;
  64   haystack_len = needle_len - 1;
  65
  66   /* Perform the search.  Abstract memory is considered to be an array
  67      of 'unsigned char' values, not an array of 'char' values.  See
  68      ISO C 99 section 6.2.6.1.  */
  69   if (needle_len < LONG_NEEDLE_THRESHOLD)
  70     return two_way_short_needle ((const unsigned char *) haystack,
  71                                  haystack_len,
  72                                  (const unsigned char *) needle_start,
  73                                  needle_len);
  74   return two_way_long_needle ((const unsigned char *) haystack, haystack_len,
  75                               (const unsigned char *) needle_start,
  76                               needle_len);
  77 }
  78
  79 #undef LONG_NEEDLE_THRESHOLD