namespace std::chrono { class tai_clock { public: using rep = a signed arithmetic type; using period = ratio<unspecified, unspecified>; using duration = chrono::duration<rep, period>; using time_point = chrono::time_point<tai_clock>; static constexpr bool is_steady = unspecified; static time_point now(); template<class Duration> static utc_time<common_type_t<Duration, seconds>> to_utc(const tai_time<Duration>&) noexcept; template<class Duration> static tai_time<common_type_t<Duration, seconds>> from_utc(const utc_time<Duration>&) noexcept; }; }

The clock tai_clock measures seconds since 1958-01-01 00:00:00
and is offset 10s ahead of UTC at this date.

That is, 1958-01-01 00:00:00 TAI is equivalent to 1957-12-31 23:59:50 UTC.

Leap seconds are not inserted into TAI.

Therefore every time a leap second is inserted into UTC,
UTC falls another second behind TAI.

For example by 2000-01-01 there had been 22 leap seconds inserted
so 2000-01-01 00:00:00 UTC is equivalent to 2000-01-01 00:00:32 TAI
(22s plus the initial 10s offset).