wcsmbs/wcsstr.c

   1 /* Copyright (C) 1995-2024 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 #ifndef WCSSTR
  32 # define WCSSTR wcsstr
  33 #endif
  34
  35 wchar_t *
  36 WCSSTR (const wchar_t *haystack, const wchar_t *needle)
  37 {
  38   wchar_t b, c;
  39
  40   if ((b = *needle) != L'\0')
  41     {
  42       haystack--;                               /* possible ANSI violation */
  43       do
  44         if ((c = *++haystack) == L'\0')
  45           goto ret0;
  46       while (c != b);
  47
  48       if (!(c = *++needle))
  49         goto foundneedle;
  50       ++needle;
  51       goto jin;
  52
  53       for (;;)
  54         {
  55           wchar_t a;
  56           const wchar_t *rhaystack, *rneedle;
  57
  58           do
  59             {
  60               if (!(a = *++haystack))
  61                 goto ret0;
  62               if (a == b)
  63                 break;
  64               if ((a = *++haystack) == L'\0')
  65                 goto ret0;
  66 shloop:       ;
  67             }
  68           while (a != b);
  69
  70 jin:      if (!(a = *++haystack))
  71             goto ret0;
  72
  73           if (a != c)
  74             goto shloop;
  75
  76           if (*(rhaystack = haystack-- + 1) == (a = *(rneedle = needle)))
  77             do
  78               {
  79                 if (a == L'\0')
  80                   goto foundneedle;
  81                 if (*++rhaystack != (a = *++needle))
  82                   break;
  83                 if (a == L'\0')
  84                   goto foundneedle;
  85               }
  86             while (*++rhaystack == (a = *++needle));
  87
  88           needle = rneedle;               /* took the register-poor approach */
  89
  90           if (a == L'\0')
  91             break;
  92         }
  93     }
  94 foundneedle:
  95   return (wchar_t*) haystack;
  96 ret0:
  97   return NULL;
  98 }
  99 /* This alias is for backward compatibility with drafts of the ISO C
 100    standard.  Unfortunately the Unix(TM) standard requires this name.  */
 101 weak_alias (wcsstr, wcswcs)