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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
/*
* This file is part of the LibreOffice project.
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*/
#pragma once
#include <cmath>
#include "arraysumfunctorinternal.hxx"
/**
* This class provides LO with Kahan summation algorithm
* About this algorithm: https://en.wikipedia.org/wiki/Kahan_summation_algorithm
* For general purpose software we assume first order error is enough.
* This class could be made constexpr if needed.
*/
class KahanSum
{
public:
constexpr KahanSum() = default;
constexpr KahanSum(double x_0)
: m_fSum(x_0)
{
}
constexpr KahanSum(double x_0, double err_0)
: m_fSum(x_0)
, m_fError(err_0)
{
}
constexpr KahanSum(const sc::op::KahanSumSimple& sum)
: m_fSum(sum.m_fSum)
, m_fError(sum.m_fError)
{
}
constexpr KahanSum(const KahanSum& fSum) = default;
public:
/**
* Adds a value to the sum using Kahan summation.
* @param x_i
*/
void add(double x_i)
{
double t = m_fSum + x_i;
if (std::abs(m_fSum) >= std::abs(x_i))
m_fError += (m_fSum - t) + x_i;
else
m_fError += (x_i - t) + m_fSum;
m_fSum = t;
}
/**
* Adds a value to the sum using Kahan summation.
* @param fSum
*/
inline void add(const KahanSum& fSum)
{
add(fSum.m_fSum);
add(fSum.m_fError);
}
/**
* Substracts a value to the sum using Kahan summation.
* @param fSum
*/
inline void subtract(const KahanSum& fSum)
{
add(-fSum.m_fSum);
add(-fSum.m_fError);
}
public:
constexpr KahanSum operator-() const
{
KahanSum fKahanSum;
fKahanSum.m_fSum = -m_fSum;
fKahanSum.m_fError = -m_fError;
return fKahanSum;
}
constexpr KahanSum& operator=(double fSum)
{
m_fSum = fSum;
m_fError = 0;
return *this;
}
constexpr KahanSum& operator=(const KahanSum& fSum) = default;
inline void operator+=(const KahanSum& fSum) { add(fSum); }
inline void operator+=(double fSum) { add(fSum); }
inline void operator-=(const KahanSum& fSum) { subtract(fSum); }
inline void operator-=(double fSum) { add(-fSum); }
inline KahanSum operator+(double fSum) const
{
KahanSum fNSum(*this);
fNSum.add(fSum);
return fNSum;
}
inline KahanSum operator+(const KahanSum& fSum) const
{
KahanSum fNSum(*this);
fNSum += fSum;
return fNSum;
}
inline KahanSum operator-(double fSum) const
{
KahanSum fNSum(*this);
fNSum.add(-fSum);
return fNSum;
}
inline KahanSum operator-(const KahanSum& fSum) const
{
KahanSum fNSum(*this);
fNSum -= fSum;
return fNSum;
}
/**
* In some parts of the code of interpr_.cxx this may be used for
* product instead of sum. This operator shall be used for that task.
*/
constexpr void operator*=(double fTimes)
{
m_fSum *= fTimes;
m_fError *= fTimes;
}
constexpr void operator/=(double fDivides)
{
m_fSum /= fDivides;
m_fError /= fDivides;
}
inline KahanSum operator*(const KahanSum& fTimes) const
{
return *this * fTimes.m_fSum + *this * fTimes.m_fError;
}
constexpr KahanSum operator*(double fTimes) const
{
KahanSum fSum(*this);
fSum *= fTimes;
return fSum;
}
inline KahanSum operator/(const KahanSum& fDivides) const { return *this / fDivides.get(); }
constexpr KahanSum operator/(double fTimes) const
{
KahanSum fSum(*this);
fSum /= fTimes;
return fSum;
}
constexpr bool operator<(const KahanSum& fSum) const { return get() < fSum.get(); }
constexpr bool operator<(double fSum) const { return get() < fSum; }
constexpr bool operator>(const KahanSum& fSum) const { return get() > fSum.get(); }
constexpr bool operator>(double fSum) const { return get() > fSum; }
constexpr bool operator<=(const KahanSum& fSum) const { return get() <= fSum.get(); }
constexpr bool operator<=(double fSum) const { return get() <= fSum; }
constexpr bool operator>=(const KahanSum& fSum) const { return get() >= fSum.get(); }
constexpr bool operator>=(double fSum) const { return get() >= fSum; }
constexpr bool operator==(const KahanSum& fSum) const
{
return fSum.m_fSum == m_fSum && fSum.m_fError == m_fError;
}
constexpr bool operator!=(const KahanSum& fSum) const
{
return fSum.m_fSum != m_fSum || fSum.m_fError != m_fError;
}
constexpr double* getSum() { return &m_fSum; }
constexpr double* getError() { return &m_fError; }
public:
/**
* Returns the final sum.
* @return final sum
*/
constexpr double get() const { return m_fSum + m_fError; }
private:
double m_fSum = 0;
double m_fError = 0;
};
/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */
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