FW: Definition of time_t changed from signed to unsigned...
Clive D.W. Feather
clive at demon.net
Fri Aug 20 08:10:13 UTC 2004
John Cowan said:
>>> A count of UTC seconds since the Epoch is the same as a count of TAI
>>> seconds
>> Only if you are talking about broken-down labels for time. But I was
>> talking about time expressed as a count of seconds. For example, the
>> two adjacent real-time seconds with broken-down labels 1998-12-31
>> 23:59:60 and 1999-01-01 00:00:00 UTC have the same count-of-seconds
>> since the epoch.
> No, I don't believe so. The two adjacent seconds you mention have the
> same _Posix_ time, but the number of elapsed UTC seconds = TAI seconds =
> SI seconds since the Epoch is not the same;
On the other hand, Paul is right to talk about UTC-TAI changing.
Perhaps a way to think about it is that UTC has two kinds of seconds:
normal and leap.
number of TAI seconds = number of UTC normal seconds + leap seconds
number of POSIX seconds = number of UTC normal seconds
TAI broken down time is based on number of TAI seconds
POSIX broken down time is based on number of POSIX seconds
UTC broken down time is based on number of UTC normal seconds
It's not really useful to talk about the number of UTC seconds elapsed,
since the whole point of UTC is its broken-down form. The only useful thing
is the number of normal seconds elapsed.
So I suppose I'm with Paul, here.
--
Clive D.W. Feather | Work: <clive at demon.net> | Tel: +44 20 8495 6138
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