runtime/WeakRandom.h

   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
  56 namespace JSC {
  57
  58 class WeakRandom {
  59 friend class JSGlobalObject; // For access to initializeSeed() during replay.
  60 public:
  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
  79 private:
  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