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      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() (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(entry->result);
     67         double result = orignalFunction(operand);
     68         entry->operand = operand;
     69         entry->result = result;
     70         return jsDoubleNumber(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
    104