/*

 * Copyright (C) 2010 Apple Inc. All rights reserved.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 * 1. Redistributions of source code must retain the above copyright

 *    notice, this list of conditions and the following disclaimer.

 * 2. Redistributions in binary form must reproduce the above copyright

 *    notice, this list of conditions and the following disclaimer in the

 *    documentation and/or other materials provided with the distribution.

 *

 * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY

 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR

 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR

 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,

 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,

 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR

 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY

 * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE

 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 

 */

#ifndef CachedTranscendentalFunction_h

#define CachedTranscendentalFunction_h

#include "JSValue.h"

namespace JSC {

extern const double NaN;

typedef double (*TranscendentalFunctionPtr)(double);

// CachedTranscendentalFunction provides a generic mechanism to cache results

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

// maps to NaN.

template<TranscendentalFunctionPtr orignalFunction>

class CachedTranscendentalFunction {

    struct CacheEntry {

        double operand;

        double result;

    };

public:

    CachedTranscendentalFunction()

        : m_cache(0)

    {

    }

    ~CachedTranscendentalFunction()

    {

        if (m_cache)

            fastFree(m_cache);

    }

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

    {

        if (UNLIKELY(!m_cache))

            initialize();

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

        if (entry->operand == operand)

            return jsDoubleNumber(exec, entry->result);

        double result = orignalFunction(operand);

        entry->operand = operand;

        entry->result = result;

        return jsDoubleNumber(exec, result);

    }

private:

    void initialize()

    {

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

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

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

            m_cache[x].operand = NaN;

            m_cache[x].result = NaN;

        }

    }

    static unsigned hash(double d)

    {

        union doubleAndUInt64 {

            double d;

            uint32_t is[2];

        } u;

        u.d = d;

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

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

        return x & (s_cacheSize - 1);

    }

    static const unsigned s_cacheSize = 0x1000;

    CacheEntry* m_cache;

};

}

#endif // CachedTranscendentalFunction_h