25 Time library [time]

25.5 Class template duration [time.duration]

25.5.9 Algorithms [time.duration.alg]

template<class Rep, class Period> constexpr duration<Rep, Period> abs(duration<Rep, Period> d);
Remarks: This function shall not participate in overload resolution unless numeric_­limits<Rep>::is_­signed is true.
Returns: If d >= d.zero(), return d, otherwise return -d.