1/*
2 * Copyright (C) 2009 Apple Inc. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 * 1. Redistributions of source code must retain the above copyright
8 *    notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 *    notice, this list of conditions and the following disclaimer in the
11 *    documentation and/or other materials provided with the distribution.
12 *
13 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
14 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
15 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
16 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
17 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
18 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
19 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
20 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
21 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
22 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
23 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
24 *
25 *
26 * Copyright (c) 2009 Ian C. Bullard
27 *
28 * Permission is hereby granted, free of charge, to any person
29 * obtaining a copy of this software and associated documentation
30 * files (the "Software"), to deal in the Software without
31 * restriction, including without limitation the rights to use,
32 * copy, modify, merge, publish, distribute, sublicense, and/or sell
33 * copies of the Software, and to permit persons to whom the
34 * Software is furnished to do so, subject to the following
35 * conditions:
36 *
37 * The above copyright notice and this permission notice shall be
38 * included in all copies or substantial portions of the Software.
39 *
40 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
41 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
42 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
43 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
44 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
45 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
46 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
47 * OTHER DEALINGS IN THE SOFTWARE.
48 */
49
50#ifndef WeakRandom_h
51#define WeakRandom_h
52
53#include <limits.h>
54#include <wtf/StdLibExtras.h>
55
56namespace JSC {
57
58class WeakRandom {
59friend class JSGlobalObject; // For access to initializeSeed() during replay.
60public:
61    WeakRandom(unsigned seed)
62    {
63        initializeSeed(seed);
64    }
65
66    // Returns the seed provided that you've never called get() or getUint32().
67    unsigned seedUnsafe() const { return m_high; }
68
69    double get()
70    {
71        return advance() / (UINT_MAX + 1.0);
72    }
73
74    unsigned getUint32()
75    {
76        return advance();
77    }
78
79private:
80    unsigned advance()
81    {
82        m_high = (m_high << 16) + (m_high >> 16);
83        m_high += m_low;
84        m_low += m_high;
85        return m_high;
86    }
87
88    void initializeSeed(unsigned seed)
89    {
90        m_low = seed ^ 0x49616E42;
91        m_high = seed;
92    }
93
94    unsigned m_low;
95    unsigned m_high;
96};
97
98} // namespace JSC
99
100#endif // WeakRandom_h
101