fsfw/contrib/fsfw_contrib/etl-20.39.4/include/etl/variance.h

///\file

/******************************************************************************
The MIT License(MIT)

Embedded Template Library.
https://github.com/ETLCPP/etl
https://www.etlcpp.com

Copyright(c) 2021 John Wellbelove

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******************************************************************************/

#ifndef ETL_VARIANCE_INCLUDED
#define ETL_VARIANCE_INCLUDED

#include "platform.h"
#include "functional.h"
#include "type_traits.h"

//#include <math.h>
#include <stdint.h>

namespace etl
{
  namespace private_variance
  {
    //***************************************************************************
    /// Types for generic variance.
    //***************************************************************************
    template <typename TInput, typename TCalc>
    struct variance_traits
    {
      typedef TCalc calc_t;
    };

    //***************************************************************************
    /// Types for float variance.
    //***************************************************************************
    template <typename TCalc>
    struct variance_traits<float, TCalc>
    {
      typedef float calc_t;
    };

    //***************************************************************************
    /// Types for double variance.
    //***************************************************************************
    template <typename TCalc>
    struct variance_traits<double, TCalc>
    {
      typedef double calc_t;
    };
  }

  //***************************************************************************
  /// Variance Type.
  //***************************************************************************
  namespace private_variance
  {
    template<typename T = void>
    struct variance_type_helper
    {
      static ETL_CONSTANT bool Sample = false;
      static ETL_CONSTANT bool Population = true;
    };

    template <typename T>
    ETL_CONSTANT bool variance_type_helper<T>::Sample;

    template <typename T>
    ETL_CONSTANT bool variance_type_helper<T>::Population;
  }

  struct variance_type : public private_variance::variance_type_helper<>
  {
  };

  //***************************************************************************
  /// Variance.
  //***************************************************************************
  template <bool Variance_Type, typename TInput, typename TCalc = TInput>
  class variance 
    : public private_variance::variance_traits<TInput, TCalc>
    , public etl::binary_function<TInput, TInput, void>
  {
  private:

    static ETL_CONSTANT int Adjustment = (Variance_Type == variance_type::Population) ? 0 : 1;

    typedef typename private_variance::variance_traits<TInput, TCalc>::calc_t calc_t;

  public:

    //*********************************
    /// Constructor.
    //*********************************
    variance()
    {
      clear();
    }

    //*********************************
    /// Constructor.
    //*********************************
    template <typename TIterator>
    variance(TIterator first, TIterator last)
    {
      clear();
      add(first, last);
    }

    //*********************************
    /// Add a pair of values.
    //*********************************
    void add(TInput value)
    {
      sum_of_squares += TCalc(value * value);
      sum            += TCalc(value);
      ++counter;
      recalculate = true;
    }

    //*********************************
    /// Add a range.
    //*********************************
    template <typename TIterator>
    void add(TIterator first, TIterator last)
    {
      while (first != last)
      {
        add(*first);
        ++first;
      }
    }

    //*********************************
    /// operator ()
    /// Add a pair of values.
    //*********************************
    void operator ()(TInput value)
    {
      add(value);
    }

    //*********************************
    /// operator ()
    /// Add a range.
    //*********************************
    template <typename TIterator>
    void operator ()(TIterator first, TIterator last)
    {
      add(first, last);
    }

    //*********************************
    /// Get the variance.
    //*********************************
    double get_variance() const
    {
      if (recalculate)
      {
        variance_value = 0.0;

        if (counter != 0)
        {
          double n = double(counter);
          double adjustment = 1.0 / (n * (n - Adjustment)) ;

          double square_of_sum = sum * sum;

          variance_value = (n * sum_of_squares - square_of_sum) * adjustment;
        }

        recalculate = false;
      }

      return variance_value;
    }

    //*********************************
    /// Get the variance.
    //*********************************
    operator double() const
    {
      return get_variance();
    }

    //*********************************
    /// Get the total number added entries.
    //*********************************
    size_t count() const
    {
      return size_t(counter);
    }

    //*********************************
    /// Clear the variance.
    //*********************************
    void clear()
    {
      sum_of_squares = calc_t(0);
      sum            = calc_t(0);
      counter        = 0U;
      variance_value = 0.0;
      recalculate    = true;
    }

  private:
  
    calc_t   sum_of_squares;
    calc_t   sum;
    uint32_t counter;
    mutable double variance_value;
    mutable bool   recalculate;
  };
}

#endif