Update.
[glibc.git] / locale / hashval.h
blob52ef8b5da9672bd8b32ff3ab6e9a04c356a29fc4
1 /* Implement simple hashing table with string based keys.
2 Copyright (C) 1994-1997, 2000, 2001, 2002 Free Software Foundation, Inc.
3 This file is part of the GNU C Library.
4 Written by Ulrich Drepper <drepper@gnu.ai.mit.edu>, October 1994.
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public
8 License as published by the Free Software Foundation; either
9 version 2.1 of the License, or (at your option) any later version.
11 The GNU C Library 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 Lesser General Public License for more details.
16 You should have received a copy of the GNU Lesser General Public
17 License along with the GNU C Library; if not, write to the Free
18 Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
19 02111-1307 USA. */
21 #ifndef hashval_t
22 # define hashval_t unsigned long int
23 #endif
24 #include <limits.h> /* For CHAR_BIT. */
26 hashval_t
27 compute_hashval (const void *key, size_t keylen)
29 size_t cnt;
30 hashval_t hval;
32 /* Compute the hash value for the given string. The algorithm
33 is taken from [Aho,Sethi,Ullman], modified to reduce the number of
34 collisions for short strings with very varied bit patterns.
35 See http://www.clisp.org/haible/hashfunc.html. */
36 cnt = 0;
37 hval = keylen;
38 while (cnt < keylen)
40 hval = (hval << 9) | (hval >> (sizeof hval * CHAR_BIT - 9));
41 hval += (hashval_t) *(((char *) key) + cnt++);
43 return hval != 0 ? hval : ~((hashval_t) 0);