FW: Definition of time_t changed from signed to unsigned...

John Cowan jcowan at reutershealth.com
Thu Aug 19 20:38:37 UTC 2004

Paul Eggert scripsit:

> When you're talking about time as a count of seconds since an epoch,
> POSIX time omits completed leap seconds.  UTC is normally thought of
> as a broken-down time like "1998-12-31 23:59:60" (the last leap
> second), but if you want to think of it as a count of seconds, then
> it's equivalent to POSIX time.  

How can that be?  A count of UTC seconds since the Epoch is the same
as a count of TAI seconds, since 1 UTC second always equals 1 TAI
second of elapsed time.  It's only when we convert from a count of seconds
to broken-out time that we see a difference between TAI and UTC.

> This announcement makes it clear that UTC-TAI was -31 seconds through
> the last leap second, and -32 seconds thereafter, and this is exactly
> how POSIX time behaves.

POSIX time counts the number of non-leap seconds since the Epoch, but
the seconds themselves are 1 TAI second = 1 UTC second = 1 SI second
in length.

One Word to write them all,             John Cowan <jcowan at reutershealth.com>
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