1 /*

     2  * Copyright (C) 2010 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 #ifndef CachedTranscendentalFunction_h

    27 #define CachedTranscendentalFunction_h

    28 

    29 #include "JSValue.h"

    30 

    31 namespace JSC {

    32 

    33 extern const double NaN;

    34 

    35 typedef double (*TranscendentalFunctionPtr)(double);

    36 

    37 // CachedTranscendentalFunction provides a generic mechanism to cache results

    38 // for pure functions with the signature "double func(double)", and where NaN

    39 // maps to NaN.

    40 template<TranscendentalFunctionPtr orignalFunction>

    41 class CachedTranscendentalFunction {

    42     struct CacheEntry {

    43         double operand;

    44         double result;

    45     };

    46 

    47 public:

    48     CachedTranscendentalFunction()

    49         : m_cache(0)

    50     {

    51     }

    52 

    53     ~CachedTranscendentalFunction()

    54     {

    55         if (m_cache)

    56             fastFree(m_cache);

    57     }

    58 

    59     JSValue operator() (ExecState* exec, double operand)

    60     {

    61         if (UNLIKELY(!m_cache))

    62             initialize();

    63         CacheEntry* entry = &m_cache[hash(operand)];

    64 

    65         if (entry->operand == operand)

    66             return jsDoubleNumber(exec, entry->result);

    67         double result = orignalFunction(operand);

    68         entry->operand = operand;

    69         entry->result = result;

    70         return jsDoubleNumber(exec, result);

    71     }

    72 

    73 private:

    74     void initialize()

    75     {

    76         // Lazily allocate the table, populate with NaN->NaN mapping.

    77         m_cache = static_cast<CacheEntry*>(fastMalloc(s_cacheSize * sizeof(CacheEntry)));

    78         for (unsigned x = 0; x < s_cacheSize; ++x) {

    79             m_cache[x].operand = NaN;

    80             m_cache[x].result = NaN;

    81         }

    82     }

    83 

    84     static unsigned hash(double d)

    85     {

    86         union doubleAndUInt64 {

    87             double d;

    88             uint32_t is[2];

    89         } u;

    90         u.d = d;

    91 

    92         unsigned x = u.is[0] ^ u.is[1];

    93         x = (x >> 20) ^ (x >> 8);

    94         return x & (s_cacheSize - 1);

    95     }

    96 

    97     static const unsigned s_cacheSize = 0x1000;

    98     CacheEntry* m_cache;

    99 };

   100 

   101 }

   102 

   103 #endif // CachedTranscendentalFunction_h