hash-string.h Source File

00001 /* Description of GNU message catalog format: string hashing function.
00002    Copyright (C) 1995, 1997, 1998, 2000, 2001 Free Software Foundation, Inc.
00003 
00004    This program is free software; you can redistribute it and/or modify
00005    it under the terms of the GNU General Public License as published by
00006    the Free Software Foundation; either version 2, or (at your option)
00007    any later version.
00008 
00009    This program is distributed in the hope that it will be useful,
00010    but WITHOUT ANY WARRANTY; without even the implied warranty of
00011    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00012    GNU General Public License for more details.
00013 
00014    You should have received a copy of the GNU General Public License
00015    along with this program; if not, write to the Free Software Foundation,
00016    Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */
00017 
00018 /* @@ end of prolog @@ */
00019 
00020 #ifndef PARAMS
00021 # if __STDC__
00022 #  define PARAMS(Args) Args
00023 # else
00024 #  define PARAMS(Args) ()
00025 # endif
00026 #endif
00027 
00028 /* We assume to have `unsigned long int' value with at least 32 bits.  */
00029 #define HASHWORDBITS 32
00030 
00031 
00032 /* Defines the so called `hashpjw' function by P.J. Weinberger
00033    [see Aho/Sethi/Ullman, COMPILERS: Principles, Techniques and Tools,
00034    1986, 1987 Bell Telephone Laboratories, Inc.]  */
00035 static unsigned long int hash_string PARAMS ((const char *__str_param));
00036 
00037 static inline unsigned long int
00038 hash_string (str_param)
00039      const char *str_param;
00040 {
00041   unsigned long int hval, g;
00042   const char *str = str_param;
00043 
00044   /* Compute the hash value for the given string.  */
00045   hval = 0;
00046   while (*str != '\0')
00047     {
00048       hval <<= 4;
00049       hval += (unsigned long int) *str++;
00050       g = hval & ((unsigned long int) 0xf << (HASHWORDBITS - 4));
00051       if (g != 0)
00052         {
00053           hval ^= g >> (HASHWORDBITS - 8);
00054           hval ^= g;
00055         }
00056     }
00057   return hval;
00058 }