System.Time.Clock Design Issues

Ketil Malde ketil+haskell at
Thu Feb 3 12:06:11 EST 2005

"Bayley, Alistair" <Alistair_Bayley at> writes:

>  - UTC/POSIX/CalenderTime are isomorphic, and represent some
> idealised notion of time where leap seconds don't exist i.e. a day
> always has duration 23:59:59.

I don't think this is correct.  In UTC, extra leap seconds are denoted
23:59:60 and the missing ones have :59:58 as the last second.  Posix's
seconds are thus not isomorphic to UTC.

>  - Most (all?) system clocks return UTC. They may slow down around leap
> seconds to support this - is this behaviour only seen on systems with NTP?

I think so.

>  - It's not possible to simply get the number of actual ticks since some
> epoch; the OS time function may slow down for leap seconds and we can't
> avoid this.

Unless you move the epoch, which is basically what POSIX does.

If I haven't seen further, it is by standing in the footprints of giants

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