modules/up/src/Core/gnu/hash.cc
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FUNCTIONS
This source file includes following functions.
- hashpjw
- multiplicativehash
- foldhash
1 /*
2 Copyright (C) 1990 Free Software Foundation
3 written by Doug Lea (dl@rocky.oswego.edu)
4
5 This file is part of the GNU C++ Library. This library is free
6 software; you can redistribute it and/or modify it under the terms of
7 the GNU Library General Public License as published by the Free
8 Software Foundation; either version 2 of the License, or (at your
9 option) any later version. This library is distributed in the hope
10 that it will be useful, but WITHOUT ANY WARRANTY; without even the
11 implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
12 PURPOSE. See the GNU Library General Public License for more details.
13 You should have received a copy of the GNU Library General Public
14 License along with this library; if not, write to the Free Software
15 Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
16 */
17
18 #ifdef __GNUG__
19 #pragma implementation
20 #endif
21
22 /*
23 some useful hash functions
24 */
25
26 unsigned int hashpjw(const char* x) // From Dragon book, p436
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27 {
28 unsigned int h = 0;
29 unsigned int g;
30
31 while (*x != 0)
32 {
33 h = (h << 4) + *x++;
34 if ((g = h & 0xf0000000) != 0)
35 h = (h ^ (g >> 24)) ^ g;
36 }
37 return h;
38 }
39
40 unsigned int multiplicativehash(int x)
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41 {
42 // uses a const close to golden ratio * pow(2,32)
43 return ((unsigned)x) * 2654435767u;
44 }
45
46
47 unsigned int foldhash(double x)
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48 {
49 union { unsigned int i[2]; double d; } u;
50 u.d = x;
51 unsigned int u0 = u.i[0];
52 unsigned int u1 = u.i[1];
53 return u0 ^ u1;
54 }
55