Time.h

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#pragma once
 
#include <algorithm>
#include <cmath>
#include <compare>
#include <limits>
 
#include "MathLib/KahanSum.h"
 
namespace NumLib
{
struct Time;
}
 
template <>
struct fmt::formatter<NumLib::Time> : fmt::ostream_formatter
{
};
 
namespace NumLib
{
struct Time
{
    constexpr explicit Time(double const time) : value_{time} {}
 
    constexpr double operator()() const { return value_(); }
 
    constexpr Time& operator+=(double const increment)
    {
        value_ += increment;
        return *this;
    }
 
    constexpr Time operator+(double const increment) const
    {
        Time result = *this;
        result += increment;
        return result;
    }
 
    constexpr Time& operator-=(double const decrement)
    {
        value_ -= decrement;
        return *this;
    }
 
    constexpr Time operator-(double const decrement) const
    {
        Time result = *this;
        result -= decrement;
        return result;
    }
 
    constexpr inline std::weak_ordering operator<=>(Time const& b) const
    {
        Time const& a = *this;
        double const diff = b() - a();
 
        double const eps = 10 * std::numeric_limits<double>::epsilon() *
                           std::max(1., (std::abs(a()) + std::abs(b())) / 2);
 
        // Keep for debugging
        // DBUG("Compare {} to {}. x is {} and y is {}. Eps {}, diff {}", a, b,
        //      x, y, eps, diff);
 
        if (diff < -eps)
        {
            return std::weak_ordering::greater;
        }
        if (diff > eps)
        {
            return std::weak_ordering::less;
        }
        return std::weak_ordering::equivalent;
    }
 
    constexpr inline bool operator==(Time const& x) const
    {
        return (*this <=> x) == std::weak_ordering::equivalent;
    }
 
    friend inline std::ostream& operator<<(std::ostream& os, Time const& t)
    {
        auto const precision = os.precision();
        return os << std::setprecision(
                         std::numeric_limits<double>::max_digits10)
                  << t() << std::setprecision(precision);
    }
 
private:
    MathLib::KahanSum value_;
};
 
}  // namespace NumLib