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 public:

    60     WeakRandom(unsigned seed)

    61         : m_low(seed ^ 0x49616E42)

    62         , m_high(seed)

    63     {

    64     }

    65 

    66     double get()

    67     {

    68         return advance() / (UINT_MAX + 1.0);

    69     }

    70 

    71 private:

    72     unsigned advance()

    73     {

    74         m_high = (m_high << 16) + (m_high >> 16);

    75         m_high += m_low;

    76         m_low += m_high;

    77         return m_high;

    78     }

    79 

    80     unsigned m_low;

    81     unsigned m_high;

    82 };

    83 

    84 } // namespace JSC

    85 

    86 #endif // WeakRandom_h