lib/wcsstr.c

   1 /* Locate a substring in a wide string.
   2    Copyright (C) 2011-2024 Free Software Foundation, Inc.
   3    Written by Bruno Haible <bruno@clisp.org>, 2011.
   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 /* Written by Bruno Haible, 1999.  */
  19
  20 #include <config.h>
  21
  22 /* Specification.  */
  23 #include <wchar.h>
  24
  25 #if NEED_LINEAR_WCSSTR
  26
  27 /* Use Two-Way algorithm, worst-case O(n+m).  */
  28
  29 # define FUNC wcsstr
  30 # define UNIT wchar_t
  31 # define RETURN_TYPE wchar_t *
  32 # define MEMCHR0(s, n) wmemchr (s, 0, n)
  33 # define STRCHR wcschr
  34 # include "wcsstr-impl.h"
  35
  36 #else
  37
  38 /* Use simple implementation, worst-case O(nm).  */
  39
  40 wchar_t *
  41 wcsstr (const wchar_t *haystack, const wchar_t *needle)
  42 {
  43   wchar_t n = needle[0];
  44
  45   /* Is needle empty?  */
  46   if (n == (wchar_t)'\0')
  47     return (wchar_t *) haystack;
  48
  49   /* Is needle nearly empty?  */
  50   if (needle[1] == (wchar_t)'\0')
  51     return wcschr (haystack, n);
  52
  53   /* Search for needle's first character.  */
  54   for (; *haystack != (wchar_t)'\0'; haystack++)
  55     {
  56       if (*haystack == n)
  57         {
  58           /* Compare with needle's remaining characters.  */
  59           const wchar_t *hptr = haystack + 1;
  60           const wchar_t *nptr = needle + 1;
  61           for (;;)
  62             {
  63               if (*hptr != *nptr)
  64                 break;
  65               hptr++; nptr++;
  66               if (*nptr == (wchar_t)'\0')
  67                 return (wchar_t *) haystack;
  68             }
  69         }
  70     }
  71
  72   return NULL;
  73 }
  74
  75 #endif