blob: 8baa2dba059d25fd44a26080c358b48ea2d1e7bb (
plain)
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
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
|
/****************************************************************************
**
** Copyright (C) 1993-2009 NVIDIA Corporation.
** Copyright (C) 2017 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of Qt 3D Studio.
**
** $QT_BEGIN_LICENSE:GPL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see https://www.qt.io/terms-conditions. For further
** information use the contact form at https://www.qt.io/contact-us.
**
** GNU General Public License Usage
** Alternatively, this file may be used under the terms of the GNU
** General Public License version 3 or (at your option) any later version
** approved by the KDE Free Qt Foundation. The licenses are as published by
** the Free Software Foundation and appearing in the file LICENSE.GPL3
** included in the packaging of this file. Please review the following
** information to ensure the GNU General Public License requirements will
** be met: https://www.gnu.org/licenses/gpl-3.0.html.
**
** $QT_END_LICENSE$
**
****************************************************************************/
#pragma once
#include "Qt3DSConfig.h"
//==============================================================================
// Namespace
//==============================================================================
namespace Q3DStudio {
//==============================================================================
/**
* Utility class transforming a string into a hash value.
*/
class CHash
{
//==============================================================================
// Methods
//==============================================================================
public: // Static utility
//==============================================================================
/**
* We use the hashing algorithm called "sdbm".
*
* This algorithm was created from sdbm (a public-domain reimplementation
* of ndbm) database library. It was found to do well in scrambling bits,
* causing better distribution of the keys and fewer splits. it also happens
* to be a good general hashing function with good distribution. the actual
* function is hash(i) = hash(i - 1) * 65599 + str[i]; what is included below
* is the faster version used in gawk. [there is even a faster, duff-device
* version] the magic constant 65599 was picked out of thin air while
* experimenting with different constants, and turns out to be a prime. this
* is one of the algorithms used in berkeley db (see sleepycat) and elsewhere.
*
* @param inString the string to hash
* @return the hash value
*/
static TStringHash HashString(const CHAR *inString)
{
TStringHash theHash = 0;
INT32 theChar = *inString;
INT32 theCount = 0;
while (theChar && (theCount < HASH_LIMIT)) {
theChar = *inString++;
theHash = theChar + (theHash << 6) + (theHash << 16) - theHash;
++theCount;
}
return theHash;
}
//==============================================================================
/**
* 31-bit hash with MSB set to 0
*
* @param inString the string to hash
* @return the 31-bit hash value
*/
static TEventCommandHash HashEventCommand(const CHAR *inString)
{
return HashString(inString) & 0x7fffffff;
}
//==============================================================================
/**
* 26-bit hash with MSBs all set to 0
*
* @param inString the string to hash
* @return the 26-bit hash value
*/
static TAttributeHash HashAttribute(const CHAR *inString)
{
return HashString(inString) & 0x03ffffff;
}
};
} // namespace Q3DStudio
|
