contrib/tar/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 #if defined _LIBC || defined HAVE_STRING_H
  32 # include <string.h>
  33 #endif
  34 #include <sys/types.h>
  35
  36 typedef unsigned chartype;
  37
  38 #undef strstr
  39
  40 char *
  41 strstr (const char *phaystack, const char *pneedle)
  42 {
  43   register const unsigned char *haystack, *needle;
  44   register chartype b, c;
  45
  46   haystack = (const unsigned char *) phaystack;
  47   needle = (const unsigned char *) pneedle;
  48
  49   b = *needle;
  50   if (b != '\0')
  51     {
  52       haystack--;                               /* possible ANSI violation */
  53       do
  54         {
  55           c = *++haystack;
  56           if (c == '\0')
  57             goto ret0;
  58         }
  59       while (c != b);
  60
  61       c = *++needle;
  62       if (c == '\0')
  63         goto foundneedle;
  64       ++needle;
  65       goto jin;
  66
  67       for (;;)
  68         {
  69           register chartype a;
  70           register const unsigned char *rhaystack, *rneedle;
  71
  72           do
  73             {
  74               a = *++haystack;
  75               if (a == '\0')
  76                 goto ret0;
  77               if (a == b)
  78                 break;
  79               a = *++haystack;
  80               if (a == '\0')
  81                 goto ret0;
  82 shloop:;    }
  83           while (a != b);
  84
  85 jin:      a = *++haystack;
  86           if (a == '\0')
  87             goto ret0;
  88
  89           if (a != c)
  90             goto shloop;
  91
  92           rhaystack = haystack-- + 1;
  93           rneedle = needle;
  94           a = *rneedle;
  95
  96           if (*rhaystack == a)
  97             do
  98               {
  99                 if (a == '\0')
 100                   goto foundneedle;
 101                 ++rhaystack;
 102                 a = *++needle;
 103                 if (*rhaystack != a)
 104                   break;
 105                 if (a == '\0')
 106                   goto foundneedle;
 107                 ++rhaystack;
 108                 a = *++needle;
 109               }
 110             while (*rhaystack == a);
 111
 112           needle = rneedle;                /* took the register-poor approach */
 113
 114           if (a == '\0')
 115             break;
 116         }
 117     }
 118 foundneedle:
 119   return (char*) haystack;
 120 ret0:
 121   return 0;
 122 }