wcsmbs/wcsstr.c

   1 /* Copyright (C) 1995-2021 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library 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 GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 /*
  19  * The original strstr() file contains the following comment:
  20  *
  21  * My personal strstr() implementation that beats most other algorithms.
  22  * Until someone tells me otherwise, I assume that this is the
  23  * fastest implementation of strstr() in C.
  24  * I deliberately chose not to comment it.  You should have at least
  25  * as much fun trying to understand it, as I had to write it :-).
  26  *
  27  * Stephen R. van den Berg, berg@pool.informatik.rwth-aachen.de */
  28
  29 #include <wchar.h>
  30
  31 wchar_t *
  32 wcsstr (const wchar_t *haystack, const wchar_t *needle)
  33 {
  34   wchar_t b, c;
  35
  36   if ((b = *needle) != L'\0')
  37     {
  38       haystack--;                               /* possible ANSI violation */
  39       do
  40         if ((c = *++haystack) == L'\0')
  41           goto ret0;
  42       while (c != b);
  43
  44       if (!(c = *++needle))
  45         goto foundneedle;
  46       ++needle;
  47       goto jin;
  48
  49       for (;;)
  50         {
  51           wchar_t a;
  52           const wchar_t *rhaystack, *rneedle;
  53
  54           do
  55             {
  56               if (!(a = *++haystack))
  57                 goto ret0;
  58               if (a == b)
  59                 break;
  60               if ((a = *++haystack) == L'\0')
  61                 goto ret0;
  62 shloop:       ;
  63             }
  64           while (a != b);
  65
  66 jin:      if (!(a = *++haystack))
  67             goto ret0;
  68
  69           if (a != c)
  70             goto shloop;
  71
  72           if (*(rhaystack = haystack-- + 1) == (a = *(rneedle = needle)))
  73             do
  74               {
  75                 if (a == L'\0')
  76                   goto foundneedle;
  77                 if (*++rhaystack != (a = *++needle))
  78                   break;
  79                 if (a == L'\0')
  80                   goto foundneedle;
  81               }
  82             while (*++rhaystack == (a = *++needle));
  83
  84           needle = rneedle;               /* took the register-poor approach */
  85
  86           if (a == L'\0')
  87             break;
  88         }
  89     }
  90 foundneedle:
  91   return (wchar_t*) haystack;
  92 ret0:
  93   return NULL;
  94 }
  95 /* This alias is for backward compatibility with drafts of the ISO C
  96    standard.  Unfortunately the Unix(TM) standard requires this name.  */
  97 weak_alias (wcsstr, wcswcs)