lib/c-strcasestr.c

   1 /* c-strcasestr.c -- case insensitive substring search in C locale
   2    Copyright (C) 2005-2020 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 3 of the License, or
   8    (at your option) 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 "c-strcasestr.h"
  22
  23 #include <stdbool.h>
  24 #include <string.h>
  25
  26 #include "c-ctype.h"
  27 #include "c-strcase.h"
  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
  35 #define CMP_FUNC(p1, p2, l)                             \
  36   c_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 case-insensitive
  40    comparison from the C locale, regardless of the current locale.  */
  41 char *
  42 c_strcasestr (const char *haystack_start, const char *needle_start)
  43 {
  44   const char *haystack = haystack_start;
  45   const char *needle = needle_start;
  46   size_t needle_len; /* Length of NEEDLE.  */
  47   size_t haystack_len; /* Known minimum length of HAYSTACK.  */
  48   bool ok = true; /* True if NEEDLE is prefix of HAYSTACK.  */
  49
  50   /* Determine length of NEEDLE, and in the process, make sure
  51      HAYSTACK is at least as long (no point processing all of a long
  52      NEEDLE if HAYSTACK is too short).  */
  53   while (*haystack && *needle)
  54     ok &= (c_tolower ((unsigned char) *haystack++)
  55            == c_tolower ((unsigned char) *needle++));
  56   if (*needle)
  57     return NULL;
  58   if (ok)
  59     return (char *) haystack_start;
  60   needle_len = needle - needle_start;
  61   haystack = haystack_start + 1;
  62   haystack_len = needle_len - 1;
  63
  64   /* Perform the search.  Abstract memory is considered to be an array
  65      of 'unsigned char' values, not an array of 'char' values.  See
  66      ISO C 99 section 6.2.6.1.  */
  67   if (needle_len < LONG_NEEDLE_THRESHOLD)
  68     return two_way_short_needle ((const unsigned char *) haystack,
  69                                  haystack_len,
  70                                  (const unsigned char *) needle_start,
  71                                  needle_len);
  72   return two_way_long_needle ((const unsigned char *) haystack, haystack_len,
  73                               (const unsigned char *) needle_start,
  74                               needle_len);
  75 }
  76
  77 #undef LONG_NEEDLE_THRESHOLD