sysdeps/generic/strstr.c

   1 /* Copyright (C) 1994, 1996 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Library General Public License as
   6    published by the Free Software Foundation; either version 2 of the
   7    License, or (at your option) any later version.
   8
   9    The GNU C Library 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 GNU
  12    Library General Public License for more details.
  13
  14    You should have received a copy of the GNU Library General Public
  15    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  16    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  17    Boston, MA 02111-1307, USA.  */
  18
  19 /*
  20  * My personal strstr() implementation that beats most other algorithms.
  21  * Until someone tells me otherwise, I assume that this is the
  22  * fastest implementation of strstr() in C.
  23  * I deliberately chose not to comment it.  You should have at least
  24  * as much fun trying to understand it, as I had to write it :-).
  25  *
  26  * Stephen R. van den Berg, berg@pool.informatik.rwth-aachen.de */
  27
  28 #include <string.h>
  29 #include <sys/types.h>
  30
  31 typedef unsigned chartype;
  32
  33 char *
  34 strstr (phaystack, pneedle)
  35      const char *phaystack;
  36      const char *pneedle;
  37 {
  38   register const unsigned char *haystack, *needle;
  39   register chartype b, c;
  40
  41   haystack = (const unsigned char *) phaystack;
  42   needle = (const unsigned char *) pneedle;
  43
  44   b = *needle;
  45   if (b != '\0')
  46     {
  47       haystack--;                               /* possible ANSI violation */
  48       do
  49         {
  50           c = *++haystack;
  51           if (c == '\0')
  52             goto ret0;
  53         }
  54       while (c != b);
  55
  56       c = *++needle;
  57       if (c == '\0')
  58         goto foundneedle;
  59       ++needle;
  60       goto jin;
  61
  62       for (;;)
  63         {
  64           register chartype a;
  65           register const unsigned char *rhaystack, *rneedle;
  66
  67           do
  68             {
  69               a = *++haystack;
  70               if (a == '\0')
  71                 goto ret0;
  72               if (a == b)
  73                 break;
  74               a = *++haystack;
  75               if (a == '\0')
  76                 goto ret0;
  77 shloop:     }
  78           while (a != b);
  79
  80 jin:      a = *++haystack;
  81           if (a == '\0')
  82             goto ret0;
  83
  84           if (a != c)
  85             goto shloop;
  86
  87           rhaystack = haystack-- + 1;
  88           rneedle = needle;
  89           a = *rneedle;
  90
  91           if (*rhaystack == a)
  92             do
  93               {
  94                 if (a == '\0')
  95                   goto foundneedle;
  96                 ++rhaystack;
  97                 a = *++needle;
  98                 if (*rhaystack != a)
  99                   break;
 100                 if (a == '\0')
 101                   goto foundneedle;
 102                 ++rhaystack;
 103                 a = *++needle;
 104               }
 105             while (*rhaystack == a);
 106
 107           needle = rneedle;             /* took the register-poor approach */
 108
 109           if (a == '\0')
 110             break;
 111         }
 112     }
 113 foundneedle:
 114   return (char*) haystack;
 115 ret0:
 116   return 0;
 117 }