lib/strcasestr.c

   1 /* Case-insensitive searching in a string.
   2    Copyright (C) 2005-2021 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, 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 <stdbool.h>
  25 #include <strings.h>
  26
  27 #define TOLOWER(Ch) (isupper (Ch) ? tolower (Ch) : (Ch))
  28
  29 /* Two-Way algorithm.  */
  30 #define RETURN_TYPE char *
  31 #define AVAILABLE(h, h_l, j, n_l)                       \
  32   (!memchr ((h) + (h_l), '\0', (j) + (n_l) - (h_l))     \
  33    && ((h_l) = (j) + (n_l)))
  34 #define CANON_ELEMENT(c) TOLOWER (c)
  35 #define CMP_FUNC(p1, p2, l)                             \
  36   strncasecmp ((const char *) (p1), (const char *) (p2), l)
  37 #include "str-two-way.h"
  38
  39 /* Find the first occurrence of NEEDLE in HAYSTACK, using
  40    case-insensitive comparison.  This function gives unspecified
  41    results in multibyte locales.  */
  42 char *
  43 strcasestr (const char *haystack_start, const char *needle_start)
  44 {
  45   const char *haystack = haystack_start;
  46   const char *needle = needle_start;
  47   size_t needle_len; /* Length of NEEDLE.  */
  48   size_t haystack_len; /* Known minimum length of HAYSTACK.  */
  49   bool ok = true; /* True if NEEDLE is prefix of HAYSTACK.  */
  50
  51   /* Determine length of NEEDLE, and in the process, make sure
  52      HAYSTACK is at least as long (no point processing all of a long
  53      NEEDLE if HAYSTACK is too short).  */
  54   while (*haystack && *needle)
  55     {
  56       ok &= (TOLOWER ((unsigned char) *haystack)
  57              == TOLOWER ((unsigned char) *needle));
  58       haystack++;
  59       needle++;
  60     }
  61   if (*needle)
  62     return NULL;
  63   if (ok)
  64     return (char *) haystack_start;
  65   needle_len = needle - needle_start;
  66   haystack = haystack_start + 1;
  67   haystack_len = needle_len - 1;
  68
  69   /* Perform the search.  Abstract memory is considered to be an array
  70      of 'unsigned char' values, not an array of 'char' values.  See
  71      ISO C 99 section 6.2.6.1.  */
  72   if (needle_len < LONG_NEEDLE_THRESHOLD)
  73     return two_way_short_needle ((const unsigned char *) haystack,
  74                                  haystack_len,
  75                                  (const unsigned char *) needle_start,
  76                                  needle_len);
  77   return two_way_long_needle ((const unsigned char *) haystack, haystack_len,
  78                               (const unsigned char *) needle_start,
  79                               needle_len);
  80 }
  81
  82 #undef LONG_NEEDLE_THRESHOLD