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Date: Fri, 6 Dec 2013 01:29:08 -0500
From: Rich Felker <>
Subject: Re: [PATCHv2] Add support for leap seconds in zoneinfo files

On Fri, Dec 06, 2013 at 01:15:52AM +0000, Laurent Bercot wrote:
> >Regarding the unfortunate coupling of timezone and leapsecond data
> >into a single file, do the zoneinfo files with leapseconds have their
> >timezone transition times stored in POSIX time or TAI?
>  TAI-10 (the 10 seconds offset is so it's the same as POSIX time
> before 1972). As I said, it's the only behaviour that makes sense:
> we're counting a number of seconds and we want it to be unambiguous.
> POSIX time would create an ambiguity for the very moment when a leap
> second happens, which defeats the purpose.

The reason I asked is that it means, if you're using TAI-10, you have
to have matching zoneinfo files for the daylight time transitions to
work correctly. This really complicates the matter of having POSIX/TAI
and TZ be separate...

> >At the very least they would have some overhead determining that
> >leapseconds aren't in use.
>  Indeed, one test at executable start. :)

At first use. Definitely not at executable start.

>  Do you have any idea what form this test would take, if we're opting
> away from TZ ?

No, I don't know.


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