Adding upstream version 4:7.4.7.upstream/4%7.4.7upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 240 insertions, 0 deletions

diff --git a/sc/inc/kahan.hxx b/sc/inc/kahan.hxx
new file mode 100644
index 000000000..6c84f6eee
--- /dev/null
+++ b/sc/inc/kahan.hxx
@@ -0,0 +1,240 @@
+/* -*- 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 <rtl/math.hxx>
+#include <cmath>
+
+/**
+  * 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.
+  *
+  * Additionally queue and remember the last recent non-zero value and add it
+  * similar to approxAdd() when obtaining the final result to further eliminate
+  * accuracy errors. (e.g. for the dreaded 0.1 + 0.2 - 0.3 != 0.0)
+  */
+
+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 KahanSum& fSum) = default;
+
+public:
+    /**
+      * Adds a value to the sum using Kahan summation.
+      * @param x_i
+      */
+    void add(double x_i)
+    {
+        if (x_i == 0.0)
+            return;
+
+        if (!m_fMem)
+        {
+            m_fMem = x_i;
+            return;
+        }
+
+        double t = m_fSum + m_fMem;
+        if (std::abs(m_fSum) >= std::abs(m_fMem))
+            m_fError += (m_fSum - t) + m_fMem;
+        else
+            m_fError += (m_fMem - t) + m_fSum;
+        m_fSum = t;
+        m_fMem = x_i;
+    }
+
+    /**
+      * 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);
+        add(fSum.m_fMem);
+    }
+
+    /**
+      * 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);
+        add(-fSum.m_fMem);
+    }
+
+public:
+    constexpr KahanSum operator-() const
+    {
+        KahanSum fKahanSum;
+        fKahanSum.m_fSum = -m_fSum;
+        fKahanSum.m_fError = -m_fError;
+        fKahanSum.m_fMem = -m_fMem;
+        return fKahanSum;
+    }
+
+    constexpr KahanSum& operator=(double fSum)
+    {
+        m_fSum = fSum;
+        m_fError = 0;
+        m_fMem = 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)
+    {
+        if (m_fMem)
+        {
+            m_fSum = get() * fTimes;
+            m_fMem = 0.0;
+        }
+        else
+        {
+            m_fSum = (m_fSum + m_fError) * fTimes;
+        }
+        m_fError = 0.0;
+    }
+
+    constexpr void operator/=(double fDivides)
+    {
+        if (m_fMem)
+        {
+            m_fSum = get() / fDivides;
+            m_fMem = 0.0;
+        }
+        else
+        {
+            m_fSum = (m_fSum + m_fError) / fDivides;
+        }
+        m_fError = 0.0;
+    }
+
+    inline KahanSum operator*(const KahanSum& fTimes) const { return get() * fTimes.get(); }
+
+    inline KahanSum operator*(double fTimes) const { return get() * fTimes; }
+
+    inline KahanSum operator/(const KahanSum& fDivides) const { return get() / fDivides.get(); }
+
+    inline KahanSum operator/(double fDivides) const { return get() / fDivides; }
+
+    inline bool operator<(const KahanSum& fSum) const { return get() < fSum.get(); }
+
+    inline bool operator<(double fSum) const { return get() < fSum; }
+
+    inline bool operator>(const KahanSum& fSum) const { return get() > fSum.get(); }
+
+    inline bool operator>(double fSum) const { return get() > fSum; }
+
+    inline bool operator<=(const KahanSum& fSum) const { return get() <= fSum.get(); }
+
+    inline bool operator<=(double fSum) const { return get() <= fSum; }
+
+    inline bool operator>=(const KahanSum& fSum) const { return get() >= fSum.get(); }
+
+    inline bool operator>=(double fSum) const { return get() >= fSum; }
+
+    inline bool operator==(const KahanSum& fSum) const { return get() == fSum.get(); }
+
+    inline bool operator!=(const KahanSum& fSum) const { return get() != fSum.get(); }
+
+public:
+    /**
+      * Returns the final sum.
+      * @return final sum
+      */
+    double get() const
+    {
+        const double fTotal = m_fSum + m_fError;
+        if (!m_fMem)
+            return fTotal;
+
+        // Check the same condition as rtl::math::approxAdd() and if true
+        // return 0.0, if false use another Kahan summation adding m_fMem.
+        if (((m_fMem < 0.0 && fTotal > 0.0) || (fTotal < 0.0 && m_fMem > 0.0))
+            && rtl::math::approxEqual(m_fMem, -fTotal))
+        {
+            /* TODO: should we reset all values to zero here for further
+             * summation, or is it better to keep them as they are? */
+            return 0.0;
+        }
+
+        // The actual argument passed to add() here does not matter as long as
+        // it is not 0, m_fMem is not 0 and will be added anyway, see add().
+        const_cast<KahanSum*>(this)->add(m_fMem);
+        const_cast<KahanSum*>(this)->m_fMem = 0.0;
+        return m_fSum + m_fError;
+    }
+
+private:
+    double m_fSum = 0;
+    double m_fError = 0;
+    double m_fMem = 0;
+};
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */