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 typedef double (*TranscendentalFunctionPtr)(double);
  34
  35 // CachedTranscendentalFunction provides a generic mechanism to cache results
  36 // for pure functions with the signature "double func(double)", and where NaN
  37 // maps to NaN.
  38 template<TranscendentalFunctionPtr orignalFunction>
  39 class CachedTranscendentalFunction {
  40     struct CacheEntry {
  41         double operand;
  42         double result;
  43     };
  44
  45 public:
  46     CachedTranscendentalFunction()
  47         : m_cache(0)
  48     {
  49     }
  50
  51     ~CachedTranscendentalFunction()
  52     {
  53         if (m_cache)
  54             fastFree(m_cache);
  55     }
  56
  57     JSValue operator() (double operand)
  58     {
  59         if (UNLIKELY(!m_cache))
  60             initialize();
  61         CacheEntry* entry = &m_cache[hash(operand)];
  62
  63         if (entry->operand == operand)
  64             return jsDoubleNumber(entry->result);
  65         double result = orignalFunction(operand);
  66         entry->operand = operand;
  67         entry->result = result;
  68         return jsDoubleNumber(result);
  69     }
  70
  71 private:
  72     void initialize()
  73     {
  74         // Lazily allocate the table, populate with NaN->NaN mapping.
  75         m_cache = static_cast<CacheEntry*>(fastMalloc(s_cacheSize * sizeof(CacheEntry)));
  76         for (unsigned x = 0; x < s_cacheSize; ++x) {
  77             m_cache[x].operand = std::numeric_limits<double>::quiet_NaN();
  78             m_cache[x].result = std::numeric_limits<double>::quiet_NaN();
  79         }
  80     }
  81
  82     static unsigned hash(double d)
  83     {
  84         union doubleAndUInt64 {
  85             double d;
  86             uint32_t is[2];
  87         } u;
  88         u.d = d;
  89
  90         unsigned x = u.is[0] ^ u.is[1];
  91         x = (x >> 20) ^ (x >> 8);
  92         return x & (s_cacheSize - 1);
  93     }
  94
  95     static const unsigned s_cacheSize = 0x1000;
  96     CacheEntry* m_cache;
  97 };
  98
  99 }
 100
 101 #endif // CachedTranscendentalFunction_h