wcsmbs/wcsstr.c

   1 /* Copyright (C) 1995, 1996 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 Library General Public License as
   6 published by the Free Software Foundation; either version 2 of the
   7 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 Library General Public License for more details.
  13
  14 You should have received a copy of the GNU Library General Public
  15 License along with the GNU C Library; see the file COPYING.LIB.  If
  16 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  17 Cambridge, MA 02139, USA.  */
  18
  19 /*
  20  * The original strstr() file contains the following comment:
  21  *
  22  * My personal strstr() implementation that beats most other algorithms.
  23  * Until someone tells me otherwise, I assume that this is the
  24  * fastest implementation of strstr() in C.
  25  * I deliberately chose not to comment it.  You should have at least
  26  * as much fun trying to understand it, as I had to write it :-).
  27  *
  28  * Stephen R. van den Berg, berg@pool.informatik.rwth-aachen.de */
  29
  30 #include <wchar.h>
  31
  32 wchar_t *
  33 wcsstr (haystack, needle)
  34      const wchar_t *haystack;
  35      const wchar_t *needle;
  36 {
  37   register wchar_t b, c;
  38
  39   if ((b = *needle) != L'\0')
  40     {
  41       haystack--;                               /* possible ANSI violation */
  42       do
  43         if ((c = *++haystack) == L'\0')
  44           goto ret0;
  45       while (c != b);
  46
  47       if (!(c = *++needle))
  48         goto foundneedle;
  49       ++needle;
  50       goto jin;
  51
  52       for (;;)
  53         {
  54           register wchar_t a;
  55           register const wchar_t *rhaystack, *rneedle;
  56
  57           do
  58             {
  59               if (!(a = *++haystack))
  60                 goto ret0;
  61               if (a == b)
  62                 break;
  63               if ((a = *++haystack) == L'\0')
  64                 goto ret0;
  65 shloop:       ;
  66             }
  67           while (a != b);
  68
  69 jin:      if (!(a = *++haystack))
  70             goto ret0;
  71
  72           if (a != c)
  73             goto shloop;
  74
  75           if (*(rhaystack = haystack-- + 1) == (a = *(rneedle = needle)))
  76             do
  77               {
  78                 if (a == L'\0')
  79                   goto foundneedle;
  80                 if (*++rhaystack != (a = *++needle))
  81                   break;
  82                 if (a == L'\0')
  83                   goto foundneedle;
  84               }
  85             while (*++rhaystack == (a = *++needle));
  86
  87           needle = rneedle;               /* took the register-poor approach */
  88
  89           if (a == L'\0')
  90             break;
  91         }
  92     }
  93 foundneedle:
  94   return (wchar_t*) haystack;
  95 ret0:
  96   return NULL;
  97 }