lib/strstr.c

   1 /* Copyright (C) 1994 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 #include <string.h>
  28 #include <sys/types.h>
  29
  30 typedef unsigned chartype;
  31
  32 char *
  33 strstr (const char *phaystack, const char *pneedle)
  34 {
  35   register const unsigned char *haystack, *needle;
  36   register chartype b, c;
  37
  38   haystack = (const unsigned char *) phaystack;
  39   needle = (const unsigned char *) pneedle;
  40
  41   b = *needle;
  42   if (b != '\0')
  43     {
  44       haystack--;                               /* possible ANSI violation */
  45       do
  46         {
  47           c = *++haystack;
  48           if (c == '\0')
  49             goto ret0;
  50         }
  51       while (c != b);
  52
  53       c = *++needle;
  54       if (c == '\0')
  55         goto foundneedle;
  56       ++needle;
  57       goto jin;
  58
  59       for (;;)
  60         {
  61           register chartype a;
  62           register const unsigned char *rhaystack, *rneedle;
  63
  64           do
  65             {
  66               a = *++haystack;
  67               if (a == '\0')
  68                 goto ret0;
  69               if (a == b)
  70                 break;
  71               a = *++haystack;
  72               if (a == '\0')
  73                 goto ret0;
  74 shloop:     }
  75           while (a != b);
  76
  77 jin:      a = *++haystack;
  78           if (a == '\0')
  79             goto ret0;
  80
  81           if (a != c)
  82             goto shloop;
  83
  84           rhaystack = haystack-- + 1;
  85           rneedle = needle;
  86           a = *rneedle;
  87
  88           if (*rhaystack == a)
  89             do
  90               {
  91                 if (a == '\0')
  92                   goto foundneedle;
  93                 ++rhaystack;
  94                 a = *++needle;
  95                 if (*rhaystack != a)
  96                   break;
  97                 if (a == '\0')
  98                   goto foundneedle;
  99                 ++rhaystack;
 100                 a = *++needle;
 101               }
 102             while (*rhaystack == a);
 103
 104           needle = rneedle;                /* took the register-poor aproach */
 105
 106           if (a == '\0')
 107             break;
 108         }
 109     }
 110 foundneedle:
 111   return (char*) haystack;
 112 ret0:
 113   return 0;
 114 }