Markus Kuhn <Markus.Kuhn@cl.cam.ac.uk> wrote:
If you have a TAI timestamp and what to print it as a TAI timestamp, then you just pass to strfxtime the TAI timestamp and specify NULL as the time zone. NULL means that the output shall be a "UTC time", but since the relationship between xtime and broken-down time is identical for both TAI and UTC, you will get the correct TAI output as well with NULL. Therefore, strfxtime can also be passed TAI timestamps with a NULL timezone_t in order to print correct TAI timestamps and strftime() does not even have to know about that this is a TAI timestamp.
I'm sorry, I still fail to follow this. 1972-01-01 00:00:00 UTC has a TIME_UTC xtime of {86400*365*2,0} and TIME_TAI has an xtime of {8600*365*2+10,0}, and TIME_UTC counts non-leapseconds while TIME_TAI counts all seconds, including leapseconds. So the xtime values for the same instant in time on these two clocks will always differ by (TAI-UTC) seconds, and values on these two clocks will differ for the same broken-down time representation (except perhaps for the brief period of history when TAI==UT1 held, if you want to speculate on the pre-1972 relationship between TAI and "UTC"). --Ken Pizzini