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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. | |
5 | ||
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. | |
10 | ||
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. | |
15 | ||
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. */ | |
20 | ||
21 | unsigned long | |
22 | compute_hashval (key, keylen) | |
23 | const void *key; | |
24 | size_t keylen; | |
25 | { | |
26 | size_t cnt; | |
27 | unsigned long int hval; | |
28 | ||
29 | /* Compute the hash value for the given string. The algorithm | |
30 | is taken from [Aho,Sethi,Ullman], modified to reduce the number of | |
31 | collisions for short strings with very varied bit patterns. | |
32 | See http://www.clisp.org/haible/hashfunc.html. */ | |
33 | cnt = 0; | |
34 | hval = keylen; | |
35 | while (cnt < keylen) | |
36 | { | |
37 | hval = (hval << 9) | (hval >> (LONGBITS - 9)); | |
38 | hval += (unsigned long int) *(((char *) key) + cnt++); | |
39 | } | |
40 | return hval != 0 ? hval : ~((unsigned long) 0); | |
41 | } |