[MaL] Implement KahanSum algorithm

MathLib/KahanSum.h

+/**
+ * \file
+ * \copyright
+ * Copyright (c) 2012-2024, OpenGeoSys Community (http://www.opengeosys.org)
+ *            Distributed under a Modified BSD License.
+ *              See accompanying file LICENSE.txt or
+ *              http://www.opengeosys.org/project/license
+ */
+
+#pragma once
+
+#include <iomanip>
+#include <ostream>
+
+namespace MathLib
+{
+
+class KahanSum
+{
+public:
+    explicit constexpr KahanSum(double const value = 0) : value_(value) {}
+
+    constexpr KahanSum& operator+=(double const increment)
+    {
+        double const y = increment - correction_;
+        double const t = value_ + y;
+        correction_ = (t - value_) - y;
+        value_ = t;
+        return *this;
+    }
+
+    constexpr double value() const { return value_; }
+    constexpr double operator()() const { return value_; }
+
+    friend inline std::ostream& operator<<(std::ostream& os, KahanSum const& x)
+    {
+        auto const precision = os.precision();
+        return os << std::setprecision(
+                         std::numeric_limits<double>::max_digits10)
+                  << x.value() << " (± " << x.correction_ << ')'
+                  << std::setprecision(precision);
+    }
+
+private:
+    double value_;
+    double correction_ = 0.;
+};
+
+}  // namespace MathLib