gnu/dist/gettext/gettext-tools/lib/strstr.c

   1 /* Copyright (C) 1994, 1999, 2002-2003 Free Software Foundation, Inc.
   2 This file is part of the GNU C Library.
   3
   4 This program is free software; you can redistribute it and/or modify
   5 it under the terms of the GNU General Public License as published by
   6 the Free Software Foundation; either version 2, or (at your option)
   7 any later version.
   8
   9 This program 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 General Public License for more details.
  13
  14 You should have received a copy of the GNU General Public License
  15 along with this program; if not, write to the Free Software
  16 Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
  17
  18 /*
  19  * My personal strstr() implementation that beats most other algorithms.
  20  * Until someone tells me otherwise, I assume that this is the
  21  * fastest implementation of strstr() in C.
  22  * I deliberately chose not to comment it.  You should have at least
  23  * as much fun trying to understand it, as I had to write it :-).
  24  *
  25  * Stephen R. van den Berg, berg@pool.informatik.rwth-aachen.de */
  26
  27 #if HAVE_CONFIG_H
  28 # include <config.h>
  29 #endif
  30
  31 #include <string.h>
  32
  33 typedef unsigned chartype;
  34
  35 #undef strstr
  36
  37 char *
  38 strstr (const char *phaystack, const char *pneedle)
  39 {
  40   register const unsigned char *haystack, *needle;
  41   register chartype b, c;
  42
  43   haystack = (const unsigned char *) phaystack;
  44   needle = (const unsigned char *) pneedle;
  45
  46   b = *needle;
  47   if (b != '\0')
  48     {
  49       haystack--;                               /* possible ANSI violation */
  50       do
  51         {
  52           c = *++haystack;
  53           if (c == '\0')
  54             goto ret0;
  55         }
  56       while (c != b);
  57
  58       c = *++needle;
  59       if (c == '\0')
  60         goto foundneedle;
  61       ++needle;
  62       goto jin;
  63
  64       for (;;)
  65         {
  66           register chartype a;
  67           register const unsigned char *rhaystack, *rneedle;
  68
  69           do
  70             {
  71               a = *++haystack;
  72               if (a == '\0')
  73                 goto ret0;
  74               if (a == b)
  75                 break;
  76               a = *++haystack;
  77               if (a == '\0')
  78                 goto ret0;
  79 shloop:;    }
  80           while (a != b);
  81
  82 jin:      a = *++haystack;
  83           if (a == '\0')
  84             goto ret0;
  85
  86           if (a != c)
  87             goto shloop;
  88
  89           rhaystack = haystack-- + 1;
  90           rneedle = needle;
  91           a = *rneedle;
  92
  93           if (*rhaystack == a)
  94             do
  95               {
  96                 if (a == '\0')
  97                   goto foundneedle;
  98                 ++rhaystack;
  99                 a = *++needle;
 100                 if (*rhaystack != a)
 101                   break;
 102                 if (a == '\0')
 103                   goto foundneedle;
 104                 ++rhaystack;
 105                 a = *++needle;
 106               }
 107             while (*rhaystack == a);
 108
 109           needle = rneedle;                /* took the register-poor approach */
 110
 111           if (a == '\0')
 112             break;
 113         }
 114     }
 115 foundneedle:
 116   return (char*) haystack;
 117 ret0:
 118   return 0;
 119 }