halfFunction.h

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//
// Copyright (c) 2002, Industrial Light & Magic, a division of Lucas
// Digital Ltd. LLC
// 
// All rights reserved.
// 
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are
// met:
// *       Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// *       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.
// *       Neither the name of Industrial Light & Magic nor the names of
// its contributors may be used to endorse or promote products derived
// from this software without specific prior written permission. 
// 
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
// "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 THE COPYRIGHT
// OWNER 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,
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
//

// Primary authors:
//     Florian Kainz <kainz@ilm.com>
//     Rod Bogart <rgb@ilm.com>


//---------------------------------------------------------------------------
//
//      halfFunction<T> -- a class for fast evaluation
//                         of half --> T functions
//
//      The constructor for a halfFunction object,
//
//          halfFunction (function,
//                        domainMin, domainMax,
//                        defaultValue,
//                        posInfValue, negInfValue,
//                        nanValue);
//
//      evaluates the function for all finite half values in the interval
//      [domainMin, domainMax], and stores the results in a lookup table.
//      For finite half values that are not in [domainMin, domainMax], the
//      constructor stores defaultValue in the table.  For positive infinity,
//      negative infinity and NANs, posInfValue, negInfValue and nanValue
//      are stored in the table.
//
//      The tabulated function can then be evaluated quickly for arbitrary
//      half values by calling the the halfFunction object's operator()
//      method.
//
//      Example:
//
//          #include <math.h>
//          #include <halfFunction.h>
//
//          halfFunction<half> hsin (sin);
//
//          halfFunction<half> hsqrt (sqrt,             // function
//                                    0, HALF_MAX,      // domain
//                                    half::qNan(),     // sqrt(x) for x < 0
//                                    half::posInf(),   // sqrt(+inf)
//                                    half::qNan(),     // sqrt(-inf)
//                                    half::qNan());    // sqrt(nan)
//
//          half x = hsin (1);
//          half y = hsqrt (3.5);
//
//---------------------------------------------------------------------------

#ifndef _HALF_FUNCTION_H_
#define _HALF_FUNCTION_H_

#include <float.h>
#include "half.h"


template <class T>
class halfFunction
{
  public:

    //------------
    // Constructor
    //------------

    template <class Function>
    halfFunction (Function f,
                  half domainMin = -HALF_MAX,
                  half domainMax =  HALF_MAX,
                  T defaultValue = 0,
                  T posInfValue  = 0,
                  T negInfValue  = 0,
                  T nanValue     = 0);

    //-----------
    // Evaluation
    //-----------

    T           operator () (half x) const;

  private:

    T           _lut[1 << 16];
};


//---------------
// Implementation
//---------------

template <class T>
template <class Function>
halfFunction<T>::halfFunction (Function f,
                               half domainMin,
                               half domainMax,
                               T defaultValue,
                               T posInfValue,
                               T negInfValue,
                               T nanValue)
{
    for (int i = 0; i < (1 << 16); i++)
    {
        half x;
        x.setBits (i);

        if (x.isNan())
            _lut[i] = nanValue;
        else if (x.isInfinity())
            _lut[i] = x.isNegative()? negInfValue: posInfValue;
        else if (x < domainMin || x > domainMax)
            _lut[i] = defaultValue;
        else
            _lut[i] = f (x);
    }
}


template <class T>
inline T
halfFunction<T>::operator () (half x) const
{
    return _lut[x.bits()];
}


#endif