lib/strstr.c

   1 /* Copyright (C) 1994, 1999 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 #include <sys/types.h>
  33
  34 typedef unsigned chartype;
  35
  36 char *
  37 strstr (const char *phaystack, const char *pneedle)
  38 {
  39   register const unsigned char *haystack, *needle;
  40   register chartype b, c;
  41
  42   haystack = (const unsigned char *) phaystack;
  43   needle = (const unsigned char *) pneedle;
  44
  45   b = *needle;
  46   if (b != '\0')
  47     {
  48       haystack--;                               /* possible ANSI violation */
  49       do
  50         {
  51           c = *++haystack;
  52           if (c == '\0')
  53             goto ret0;
  54         }
  55       while (c != b);
  56
  57       c = *++needle;
  58       if (c == '\0')
  59         goto foundneedle;
  60       ++needle;
  61       goto jin;
  62
  63       for (;;)
  64         {
  65           register chartype a;
  66           register const unsigned char *rhaystack, *rneedle;
  67
  68           do
  69             {
  70               a = *++haystack;
  71               if (a == '\0')
  72                 goto ret0;
  73               if (a == b)
  74                 break;
  75               a = *++haystack;
  76               if (a == '\0')
  77                 goto ret0;
  78 shloop:;    }
  79           while (a != b);
  80
  81 jin:      a = *++haystack;
  82           if (a == '\0')
  83             goto ret0;
  84
  85           if (a != c)
  86             goto shloop;
  87
  88           rhaystack = haystack-- + 1;
  89           rneedle = needle;
  90           a = *rneedle;
  91
  92           if (*rhaystack == a)
  93             do
  94               {
  95                 if (a == '\0')
  96                   goto foundneedle;
  97                 ++rhaystack;
  98                 a = *++needle;
  99                 if (*rhaystack != a)
 100                   break;
 101                 if (a == '\0')
 102                   goto foundneedle;
 103                 ++rhaystack;
 104                 a = *++needle;
 105               }
 106             while (*rhaystack == a);
 107
 108           needle = rneedle;                /* took the register-poor aproach */
 109
 110           if (a == '\0')
 111             break;
 112         }
 113     }
 114 foundneedle:
 115   return (char*) haystack;
 116 ret0:
 117   return 0;
 118 }