Logo Search packages:      
Sourcecode: coreutils version File versions

strstr.c

/* Copyright (C) 1994, 1999, 2002-2003 Free Software Foundation, Inc.
This file is part of the GNU C Library.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */

/*
 * My personal strstr() implementation that beats most other algorithms.
 * Until someone tells me otherwise, I assume that this is the
 * fastest implementation of strstr() in C.
 * I deliberately chose not to comment it.  You should have at least
 * as much fun trying to understand it, as I had to write it :-).
 *
 * Stephen R. van den Berg, berg@pool.informatik.rwth-aachen.de   */

#if HAVE_CONFIG_H
# include <config.h>
#endif

#include <string.h>

typedef unsigned chartype;

#undef strstr

char *
strstr (const char *phaystack, const char *pneedle)
{
  register const unsigned char *haystack, *needle;
  register chartype b, c;

  haystack = (const unsigned char *) phaystack;
  needle = (const unsigned char *) pneedle;

  b = *needle;
  if (b != '\0')
    {
      haystack--;                   /* possible ANSI violation */
      do
      {
        c = *++haystack;
        if (c == '\0')
          goto ret0;
      }
      while (c != b);

      c = *++needle;
      if (c == '\0')
      goto foundneedle;
      ++needle;
      goto jin;

      for (;;)
        {
          register chartype a;
        register const unsigned char *rhaystack, *rneedle;

        do
          {
            a = *++haystack;
            if (a == '\0')
            goto ret0;
            if (a == b)
            break;
            a = *++haystack;
            if (a == '\0')
            goto ret0;
shloop:;    }
          while (a != b);

jin:    a = *++haystack;
        if (a == '\0')
          goto ret0;

        if (a != c)
          goto shloop;

        rhaystack = haystack-- + 1;
        rneedle = needle;
        a = *rneedle;

        if (*rhaystack == a)
          do
            {
            if (a == '\0')
              goto foundneedle;
            ++rhaystack;
            a = *++needle;
            if (*rhaystack != a)
              break;
            if (a == '\0')
              goto foundneedle;
            ++rhaystack;
            a = *++needle;
            }
          while (*rhaystack == a);

        needle = rneedle;              /* took the register-poor approach */

        if (a == '\0')
          break;
        }
    }
foundneedle:
  return (char*) haystack;
ret0:
  return 0;
}

Generated by  Doxygen 1.6.0   Back to index