kahan_sum.hpp

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#pragma once


namespace waveblocks {
    namespace math {
        template<class T>
        class KahanSum
        {
        private:
            T sum_;

            T c_;

            T y_;
            T t_;

        public:
            KahanSum() = default;

            KahanSum(const T &zero)
                : sum_(zero)
                , c_(zero)
            { }

            KahanSum(const KahanSum<T> &that) = default;

            KahanSum &operator=(const KahanSum<T> &that) = default;

            KahanSum &operator+=(const T &summand)
            {
                y_ = summand - c_;
                t_ = sum_ + y_;
                c_ = (t_ - sum_) - y_;
                sum_ = t_;
                return *this;
            }

            const T &operator()() const
            {
                return sum_;
            }
        };
    }
}