wcsmbs/wcsstr.c

   1 /* Copyright (C) 1995-2015 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    <http://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 (haystack, needle)
  33      const wchar_t *haystack;
  34      const wchar_t *needle;
  35 {
  36   wchar_t b, c;
  37
  38   if ((b = *needle) != L'\0')
  39     {
  40       haystack--;                               /* possible ANSI violation */
  41       do
  42         if ((c = *++haystack) == L'\0')
  43           goto ret0;
  44       while (c != b);
  45
  46       if (!(c = *++needle))
  47         goto foundneedle;
  48       ++needle;
  49       goto jin;
  50
  51       for (;;)
  52         {
  53           wchar_t a;
  54           const wchar_t *rhaystack, *rneedle;
  55
  56           do
  57             {
  58               if (!(a = *++haystack))
  59                 goto ret0;
  60               if (a == b)
  61                 break;
  62               if ((a = *++haystack) == L'\0')
  63                 goto ret0;
  64 shloop:       ;
  65             }
  66           while (a != b);
  67
  68 jin:      if (!(a = *++haystack))
  69             goto ret0;
  70
  71           if (a != c)
  72             goto shloop;
  73
  74           if (*(rhaystack = haystack-- + 1) == (a = *(rneedle = needle)))
  75             do
  76               {
  77                 if (a == L'\0')
  78                   goto foundneedle;
  79                 if (*++rhaystack != (a = *++needle))
  80                   break;
  81                 if (a == L'\0')
  82                   goto foundneedle;
  83               }
  84             while (*++rhaystack == (a = *++needle));
  85
  86           needle = rneedle;               /* took the register-poor approach */
  87
  88           if (a == L'\0')
  89             break;
  90         }
  91     }
  92 foundneedle:
  93   return (wchar_t*) haystack;
  94 ret0:
  95   return NULL;
  96 }
  97 /* This alias is for backward compatibility with drafts of the ISO C
  98    standard.  Unfortunately the Unix(TM) standard requires this name.  */
  99 weak_alias (wcsstr, wcswcs)