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halfFunction.h

///////////////////////////////////////////////////////////////////////////
//
// 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,
// 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.
//
///////////////////////////////////////////////////////////////////////////

// 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

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