lib/wcsstr-impl.h

   1 /* Locate a substring in a wide string.
   2    Copyright (C) 1999, 2011-2025 Free Software Foundation, Inc.
   3
   4    This file is free software: you can redistribute it and/or modify
   5    it under the terms of the GNU Lesser General Public License as
   6    published by the Free Software Foundation; either version 2.1 of the
   7    License, or (at your option) any later version.
   8
   9    This file is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12    GNU Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public License
  15    along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
  16
  17 /* Written by Eric Blake, 2008.  */
  18
  19 #define AVAILABLE(h, h_l, j, n_l)                       \
  20   (!MEMCHR0 ((h) + (h_l), (j) + (n_l) - (h_l))          \
  21    && ((h_l) = (j) + (n_l)))
  22 #include "wcs-two-way.h"
  23
  24 RETURN_TYPE
  25 FUNC (const UNIT *haystack_start, const UNIT *needle_start)
  26 {
  27   const UNIT *haystack = haystack_start;
  28   const UNIT *needle = needle_start;
  29   size_t needle_len; /* Length of NEEDLE.  */
  30   size_t haystack_len; /* Known minimum length of HAYSTACK.  */
  31   bool ok = true; /* True if NEEDLE is prefix of HAYSTACK.  */
  32
  33   /* Determine length of NEEDLE, and in the process, make sure
  34      HAYSTACK is at least as long (no point processing all of a long
  35      NEEDLE if HAYSTACK is too short).  */
  36   while (*haystack && *needle)
  37     ok &= *haystack++ == *needle++;
  38   if (*needle)
  39     return NULL;
  40   if (ok)
  41     return (RETURN_TYPE) haystack_start;
  42
  43   /* Reduce the size of haystack using STRCHR, since it has a smaller
  44      linear coefficient than the Two-Way algorithm.  */
  45   needle_len = needle - needle_start;
  46   haystack = STRCHR (haystack_start + 1, *needle_start);
  47   if (!haystack || __builtin_expect (needle_len == 1, 0))
  48     return (RETURN_TYPE) haystack;
  49   needle -= needle_len;
  50   haystack_len = (haystack > haystack_start + needle_len ? 1
  51                   : needle_len + haystack_start - haystack);
  52
  53   /* Perform the search.  */
  54   return two_way_short_needle (haystack, haystack_len,
  55                                needle, needle_len);
  56 }