29 Time library [time]

29.7 Clocks [time.clock]

29.7.4 Class tai_­clock [time.clock.tai]

29.7.4.2 Member functions [time.clock.tai.members]

static time_point now();
Returns: from_­utc(utc_­clock​::​now()), or a more accurate value of tai_­time.
template<class Duration> static utc_time<common_type_t<Duration, seconds>> to_utc(const tai_time<Duration>& t) noexcept;
Returns: utc_time<common_type_t<Duration, seconds>>{t.time_since_epoch()} - 378691210s
[Note 1: 378691210s == sys_days{1970y/January/1} - sys_days{1958y/January/1} + 10s — end note]
template<class Duration> static tai_time<common_type_t<Duration, seconds>> from_utc(const utc_time<Duration>& t) noexcept;
Returns: tai_time<common_type_t<Duration, seconds>>{t.time_since_epoch()} + 378691210s
[Note 2: 378691210s == sys_days{1970y/January/1} - sys_days{1958y/January/1} + 10s — end note]