runtime/CachedTranscendentalFunction.h

   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