gnu/dist/grep/intl/hash-string.h

   1 /*      $NetBSD$        */
   2
   3 /* Description of GNU message catalog format: string hashing function.
   4    Copyright (C) 1995, 1997, 1998, 2000, 2001 Free Software Foundation, Inc.
   5
   6    This program is free software; you can redistribute it and/or modify it
   7    under the terms of the GNU Library General Public License as published
   8    by the Free Software Foundation; either version 2, or (at your option)
   9    any later version.
  10
  11    This program is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Library General Public License for more details.
  15
  16    You should have received a copy of the GNU Library General Public
  17    License along with this program; if not, write to the Free Software
  18    Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307,
  19    USA.  */
  20
  21 /* @@ end of prolog @@ */
  22
  23 #ifndef PARAMS
  24 # if __STDC__ || defined __GNUC__ || defined __SUNPRO_C || defined __cplusplus || __PROTOTYPES
  25 #  define PARAMS(Args) Args
  26 # else
  27 #  define PARAMS(Args) ()
  28 # endif
  29 #endif
  30
  31 /* We assume to have `unsigned long int' value with at least 32 bits.  */
  32 #define HASHWORDBITS 32
  33
  34
  35 /* Defines the so called `hashpjw' function by P.J. Weinberger
  36    [see Aho/Sethi/Ullman, COMPILERS: Principles, Techniques and Tools,
  37    1986, 1987 Bell Telephone Laboratories, Inc.]  */
  38 static unsigned long int hash_string PARAMS ((const char *__str_param));
  39
  40 static inline unsigned long int
  41 hash_string (str_param)
  42      const char *str_param;
  43 {
  44   unsigned long int hval, g;
  45   const char *str = str_param;
  46
  47   /* Compute the hash value for the given string.  */
  48   hval = 0;
  49   while (*str != '\0')
  50     {
  51       hval <<= 4;
  52       hval += (unsigned long int) *str++;
  53       g = hval & ((unsigned long int) 0xf << (HASHWORDBITS - 4));
  54       if (g != 0)
  55         {
  56           hval ^= g >> (HASHWORDBITS - 8);
  57           hval ^= g;
  58         }
  59     }
  60   return hval;
  61 }