FreeBSD handles leapsecond correctly

Peter Jeremy PeterJeremy at
Mon Jan 2 22:18:10 PST 2006

On Mon, 2006-Jan-02 22:10:46 -0700, M. Warner Losh wrote:
>The biggest problem with compiling leap seconds into this is that you
>can only be sure that leap seconds are right for at most 6 months.
>Sure, you can make statistical statements about how likely a leap
>second is or isn't going to be, but this non-determinism is a big
>problem.  There's no way you can deploy a system and have a sane leap
>second table without a connection to the outside world...

The Islamic calendar is based on lunar _sightings_: If it's cloudy,
the calendar shifts a day.  This wreaks even more havoc than the
odd leap-second and many Islamic countries have therefore switched
to using almanac based dates.

Actually, I'd suggest that you can't build a system that keeps any
sort of accurate time without a connection to the outside world or a
quite substantial budget.  If you assume a leap second every 5 years
then the difference between UTC and TAI is about 6e-9 - being able
to tell the difference requires an atomic clock - which isn't common
in embedded systems.

>Leap seconds are hard and I hate them.

Which of the competing alternatives would you prefer?

Peter Jeremy

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