blob: f1b75ae6a94a985f8ca8c285d94eb42867ad196b (
plain) (
blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
|
/* Implement simple hashing table with string based keys.
Copyright (C) 1994-2019 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Written by Ulrich Drepper <drepper@gnu.ai.mit.edu>, October 1994.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<http://www.gnu.org/licenses/>. */
#ifndef hashval_t
# define hashval_t unsigned long int
#endif
#include <limits.h> /* For CHAR_BIT. */
hashval_t
compute_hashval (const void *key, size_t keylen)
{
size_t cnt;
hashval_t hval;
/* Compute the hash value for the given string. The algorithm
is taken from [Aho,Sethi,Ullman], modified to reduce the number of
collisions for short strings with very varied bit patterns.
See http://www.clisp.org/haible/hashfunc.html. */
cnt = 0;
hval = keylen;
while (cnt < keylen)
{
hval = (hval << 9) | (hval >> (sizeof hval * CHAR_BIT - 9));
hval += (hashval_t) ((const unsigned char *) key)[cnt++];
}
return hval != 0 ? hval : ~((hashval_t) 0);
}
|
