chrono helper(boost & std chrono inter-convertion)

chrono_helper.cpp

#include <boost/chrono.hpp>
#include <chrono>

// from https://github.com/boostorg/chrono/issues/41#issuecomment-538932927
namespace sc = ::std::chrono;
namespace bc = ::boost::chrono;
namespace chrono_helper {

    // std::is_same_v<to_std_ratio_t<boost::ratio<N,D>>, std::ratio<N,D>>
    // if and only if N, D are coprime and D is positive
    template<typename Ratio>
    using to_std_ratio_t = std::ratio<Ratio::num, Ratio::den>;

    // std::is_same_v<to_boost_ratio_t<std::ratio<N,D>>, boost::ratio<N,D>>
    // if and only if N, D are coprime and D is positive
    template<typename Ratio>
    using to_boost_ratio_t = boost::ratio<Ratio::num, Ratio::den>;

    template<typename Rep, typename Period> inline constexpr
    sc::duration<Rep, to_std_ratio_t<Period>>
    to_std_chrono(const bc::duration<Rep, Period> &d)
    {
        return sc::duration<Rep, to_std_ratio_t<Period>>
                (d.count());
    }

    template<typename Rep, typename Period> inline constexpr
    sc::time_point<sc::system_clock,
                   sc::duration<Rep, to_std_ratio_t<Period>>>
    to_std_chrono(const bc::time_point<bc::system_clock,
                                       bc::duration<Rep, Period>> &t)
    {
        // Assuming same epoch
        return sc::time_point<sc::system_clock,
                              sc::duration<Rep, to_std_ratio_t<Period>>>
                (to_std_chrono(t.time_since_epoch()));
    }

    template<typename Rep, typename Period> inline constexpr
    bc::duration<Rep, to_boost_ratio_t<Period>>
    to_boost_chrono(const sc::duration<Rep, Period> &d)
    {
        return bc::duration<Rep, to_boost_ratio_t<Period>>
                (d.count());
    }

    template<typename Rep, typename Period> static constexpr
    bc::time_point<bc::system_clock,
                   bc::duration<Rep, to_boost_ratio_t<Period>>>
    to_boost_chrono(const sc::time_point<sc::system_clock,
                                         sc::duration<Rep, Period>> &t)
    {
        // Assuming same epoch
        return bc::time_point<bc::system_clock,
                              bc::duration<Rep, to_boost_ratio_t<Period>>>
                (to_boost_chrono(t.time_since_epoch()));
    }
}