string/strstr.c

   1 /* Return the offset of one string within another.
   2    Copyright (C) 1994,1996,1997,2000,2001,2003 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  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 #if HAVE_CONFIG_H
  30 # include <config.h>
  31 #endif
  32
  33 #if defined _LIBC || defined HAVE_STRING_H
  34 # include <string.h>
  35 #endif
  36
  37 typedef unsigned chartype;
  38
  39 #undef strstr
  40
  41 char *
  42 strstr (phaystack, pneedle)
  43      const char *phaystack;
  44      const char *pneedle;
  45 {
  46   const unsigned char *haystack, *needle;
  47   chartype b;
  48   const unsigned char *rneedle;
  49
  50   haystack = (const unsigned char *) phaystack;
  51
  52   if ((b = *(needle = (const unsigned char *) pneedle)))
  53     {
  54       chartype c;
  55       haystack--;               /* possible ANSI violation */
  56
  57       {
  58         chartype a;
  59         do
  60           if (!(a = *++haystack))
  61             goto ret0;
  62         while (a != b);
  63       }
  64
  65       if (!(c = *++needle))
  66         goto foundneedle;
  67       ++needle;
  68       goto jin;
  69
  70       for (;;)
  71         {
  72           {
  73             chartype a;
  74             if (0)
  75             jin:{
  76                 if ((a = *++haystack) == c)
  77                   goto crest;
  78               }
  79             else
  80               a = *++haystack;
  81             do
  82               {
  83                 for (; a != b; a = *++haystack)
  84                   {
  85                     if (!a)
  86                       goto ret0;
  87                     if ((a = *++haystack) == b)
  88                       break;
  89                     if (!a)
  90                       goto ret0;
  91                   }
  92               }
  93             while ((a = *++haystack) != c);
  94           }
  95         crest:
  96           {
  97             chartype a;
  98             {
  99               const unsigned char *rhaystack;
 100               if (*(rhaystack = haystack-- + 1) == (a = *(rneedle = needle)))
 101                 do
 102                   {
 103                     if (!a)
 104                       goto foundneedle;
 105                     if (*++rhaystack != (a = *++needle))
 106                       break;
 107                     if (!a)
 108                       goto foundneedle;
 109                   }
 110                 while (*++rhaystack == (a = *++needle));
 111               needle = rneedle; /* took the register-poor aproach */
 112             }
 113             if (!a)
 114               break;
 115           }
 116         }
 117     }
 118 foundneedle:
 119   return (char *) haystack;
 120 ret0:
 121   return 0;
 122 }
 123 libc_hidden_builtin_def (strstr)