intl/hash-string.h

   1 /* Implements a string hashing function.
   2    Copyright (C) 1995, 1997, 1998, 2000 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 Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the 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    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, write to the Free
  17    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  18    02111-1307 USA.  */
  19
  20 /* @@ end of prolog @@ */
  21
  22 #ifndef PARAMS
  23 # if __STDC__
  24 #  define PARAMS(Args) Args
  25 # else
  26 #  define PARAMS(Args) ()
  27 # endif
  28 #endif
  29
  30 /* We assume to have `unsigned long int' value with at least 32 bits.  */
  31 #define HASHWORDBITS 32
  32
  33
  34 /* Defines the so called `hashpjw' function by P.J. Weinberger
  35    [see Aho/Sethi/Ullman, COMPILERS: Principles, Techniques and Tools,
  36    1986, 1987 Bell Telephone Laboratories, Inc.]  */
  37 static unsigned long int hash_string PARAMS ((const char *__str_param));
  38
  39 static inline unsigned long int
  40 hash_string (str_param)
  41      const char *str_param;
  42 {
  43   unsigned long int hval, g;
  44   const char *str = str_param;
  45
  46   /* Compute the hash value for the given string.  */
  47   hval = 0;
  48   while (*str != '\0')
  49     {
  50       hval <<= 4;
  51       hval += (unsigned long int) *str++;
  52       g = hval & ((unsigned long int) 0xf << (HASHWORDBITS - 4));
  53       if (g != 0)
  54         {
  55           hval ^= g >> (HASHWORDBITS - 8);
  56           hval ^= g;
  57         }
  58     }
  59   return hval;
  60 }