chrono.h

 
#if __cplusplus < 201703L
 
#include <chrono>       // std::chrono
#include <type_traits>  // std::enable_if_t
 
namespace std {
namespace chrono {
 
template<class T> struct is_duration : std::false_type {};
template<class Rep, class Period> struct is_duration<std::chrono::duration<Rep, Period>>
    : std::true_type {};
 
template<class To, class Rep, class Period, class = std::enable_if_t<is_duration<To>{}>>
constexpr To floor(const duration<Rep, Period>& d) {
    To t = std::chrono::duration_cast<To>(d);
    if (t > d) return t - To{1};
    return t;
}
 
template<class To, class Clock, class FromDuration, class = std::enable_if_t<is_duration<To>{}>>
constexpr std::chrono::time_point<Clock, To>
floor(const std::chrono::time_point<Clock, FromDuration>& tp) {
    return std::chrono::time_point<Clock, To>{ std::chrono::floor<To>(tp.time_since_epoch()) };
}
 
}  // namespace chrono
}  // namespace std
 
#endif  // __cplusplus