sysdeps/generic/strstr.c

   1 /* Return the offset of one string within another.
   2    Copyright (C) 1994, 1996, 1997 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 Library General Public License as
   7    published by the Free Software Foundation; either version 2 of the
   8    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    Library General Public License for more details.
  14
  15    You should have received a copy of the GNU Library General Public
  16    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  17    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  18    Boston, MA 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   register const unsigned char *haystack, *needle;
  47   register chartype b, c;
  48
  49   haystack = (const unsigned char *) phaystack;
  50   needle = (const unsigned char *) pneedle;
  51
  52   b = *needle;
  53   if (b != '\0')
  54     {
  55       haystack--;                               /* possible ANSI violation */
  56       do
  57         {
  58           c = *++haystack;
  59           if (c == '\0')
  60             goto ret0;
  61         }
  62       while (c != b);
  63
  64       c = *++needle;
  65       if (c == '\0')
  66         goto foundneedle;
  67       ++needle;
  68       goto jin;
  69
  70       for (;;)
  71         {
  72           register chartype a;
  73           register const unsigned char *rhaystack, *rneedle;
  74
  75           do
  76             {
  77               a = *++haystack;
  78               if (a == '\0')
  79                 goto ret0;
  80               if (a == b)
  81                 break;
  82               a = *++haystack;
  83               if (a == '\0')
  84                 goto ret0;
  85 shloop:     }
  86           while (a != b);
  87
  88 jin:      a = *++haystack;
  89           if (a == '\0')
  90             goto ret0;
  91
  92           if (a != c)
  93             goto shloop;
  94
  95           rhaystack = haystack-- + 1;
  96           rneedle = needle;
  97           a = *rneedle;
  98
  99           if (*rhaystack == a)
 100             do
 101               {
 102                 if (a == '\0')
 103                   goto foundneedle;
 104                 ++rhaystack;
 105                 a = *++needle;
 106                 if (*rhaystack != a)
 107                   break;
 108                 if (a == '\0')
 109                   goto foundneedle;
 110                 ++rhaystack;
 111                 a = *++needle;
 112               }
 113             while (*rhaystack == a);
 114
 115           needle = rneedle;             /* took the register-poor approach */
 116
 117           if (a == '\0')
 118             break;
 119         }
 120     }
 121 foundneedle:
 122   return (char*) haystack;
 123 ret0:
 124   return 0;
 125 }