gamma.h

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/******************************************************************************
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Embedded Template Library.
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Copyright(c) 2021 John Wellbelove
 
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#ifndef ETL_GAMMA_INCLUDED
#define ETL_GAMMA_INCLUDED
 
#include "platform.h"
#include "functional.h"
#include "type_traits.h"
 
#include <math.h>
#include <stdint.h>
 
namespace etl
{
  //***************************************************************************
  //***************************************************************************
  template <typename TInput>
  class gamma_encode : public etl::unary_function<TInput, TInput>
  {
  public:
 
    //*********************************
    //*********************************
    gamma_encode(double gamma_, TInput maximum_)
      : one_over_gamma(1.0 / gamma_)
      , maximum(maximum_)
    {      
    }
 
    //*********************************
    //*********************************
    TInput operator ()(TInput value) const
    {
      // Calculate intermediate result because rounding + optimization
      // lead to wrong values when returning directly (test on i386)
      const double result = maximum * pow(double(value) / maximum, one_over_gamma);
      
      return TInput(result);
    }
 
  private:
 
    const double one_over_gamma;
    const double maximum;
  };
 
  //***************************************************************************
  //***************************************************************************
  template <typename TInput>
  class gamma_decode : public etl::unary_function<TInput, TInput>
  {
  public:
 
    //*********************************
    //*********************************
    gamma_decode(double gamma_, TInput maximum_)
      : gamma(gamma_)
      , maximum(maximum_)
    {      
    }
 
    //*********************************
    //*********************************
    TInput operator ()(TInput value) const
    {
      // Calculate intermediate result because rounding + optimization
      // lead to wrong values when returning directly (test on i386)
      const double result = maximum * pow(double(value) / maximum, gamma);
      return TInput(result);
    }
 
  private:
 
    const double gamma;
    const double maximum;
  };
}
 
#endif