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[bison.git] / intl / hash-string.h

/* Description of GNU message catalog format: string hashing function.
   Copyright (C) 1995, 1997, 1998, 2000, 2001 Free Software Foundation, Inc.

   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.  */

/* @@ end of prolog @@ */

#ifndef PARAMS
# if __STDC__
#  define PARAMS(Args) Args
# else
#  define PARAMS(Args) ()
# endif
#endif

/* We assume to have `unsigned long int' value with at least 32 bits.  */
#define HASHWORDBITS 32


/* Defines the so called `hashpjw' function by P.J. Weinberger
   [see Aho/Sethi/Ullman, COMPILERS: Principles, Techniques and Tools,
   1986, 1987 Bell Telephone Laboratories, Inc.]  */
static unsigned long int hash_string PARAMS ((const char *__str_param));

static inline unsigned long int
hash_string (str_param)
     const char *str_param;
{
  unsigned long int hval, g;
  const char *str = str_param;

  /* Compute the hash value for the given string.  */
  hval = 0;
  while (*str != '\0')
    {
      hval <<= 4;
      hval += (unsigned long int) *str++;
      g = hval & ((unsigned long int) 0xf << (HASHWORDBITS - 4));
      if (g != 0)
	{
	  hval ^= g >> (HASHWORDBITS - 8);
	  hval ^= g;
	}
    }
  return hval;
}