Re: [Tzdist] Fun with tzdata and non-Gregorian DST rules

Tim Parenti <tim@timtimeonline.com> Fri, 13 November 2015 19:07 UTC

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Date: Fri, 13 Nov 2015 14:06:56 -0500
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From: Tim Parenti <tim@timtimeonline.com>
To: Ken Murchison <murch@andrew.cmu.edu>
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Subject: Re: [Tzdist] Fun with tzdata and non-Gregorian DST rules
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On 13 November 2015 at 13:50, Ken Murchison <murch@andrew.cmu.edu>; wrote:

> I found this interesting/amusing so I thought I'd share it.
>

Cool!

I briefly looked for other zones based on lunisolar calendars and didn't
> come up with any.  The Brazilian rules are essentially based around Easter
> and there is no way that I have found to represent Easter as a recurrence
> rule in iCalendar.
>
> All of this is just for fun at this point because I don't believe that any
> calendaring clients have support for RSCALE yet.
>

I've been thinking on similar things for a while... currently tz only
bothers with transitions within the 32-bit POSIX timestamp range, even
though it's technically 64-bit capable.  When it comes time for tz to start
caring about transitions beyond 2038 (which I'd argue is sooner than
later!), we may need to take a hard look at natively supporting other
calendaring systems like RSCALE, in order to be able to compactly represent
transitions N years in the future for any reasonable N.

The toughest parts will be dealing with places where the rules are based on
a mixture of calendaring systems, such as Africa/Cairo.

--
Tim Parenti