halfFunction.h

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//
// SPDX-License-Identifier: BSD-3-Clause
// Copyright Contributors to the OpenEXR Project.
//

//---------------------------------------------------------------------------
//
//      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_

/// @cond Doxygen_Suppress

#include "half.h"

#include "ImathConfig.h"
#ifndef IMATH_HAVE_LARGE_STACK
#    include <string.h> // need this for memset
#else
#endif

#include <float.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);

#ifndef IMATH_HAVE_LARGE_STACK
    ~halfFunction () { delete[] _lut; }
    halfFunction (const halfFunction&) = delete;
    halfFunction& operator= (const halfFunction&) = delete;
    halfFunction (halfFunction&&)                 = delete;
    halfFunction& operator= (halfFunction&&) = delete;
#endif

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

    T operator() (half x) const;

private:
#ifdef IMATH_HAVE_LARGE_STACK
    T _lut[1 << 16];
#else
    T* _lut;
#endif
};

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

template <class T>
template <class Function>
halfFunction<T>::halfFunction (
    Function f,
    half     domainMin,
    half     domainMax,
    T        defaultValue,
    T        posInfValue,
    T        negInfValue,
    T        nanValue)
{
#ifndef IMATH_HAVE_LARGE_STACK
    _lut = new T[1 << 16];
#endif

    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 ()];
}

/// @endcond

#endif