[tz] zdump broken with latest Cairo changes?

[Tim Parenti]

I'm only counting four transitions per year in your output (eight lines)
and, yes, this is expected.

This year, Ramadan is approximately 5 June to 5 July. Because it moves
forward ~11 days per year, as it moves earlier in the spring in 2017
through 2019, it remains wholly within our predicted DST period from
late-April through late-October. Since Egypt has tended to suspend DST for
Ramadan in the past, this nominally requires four clock changes per year:
one to spring forward, one to suspend for Ramadan, one to return after
Ramadan, and one to fall back.

In 2020–2022, Ramadan does not overlap in this way, and so DST is simply
delayed by a few weeks until after Ramadan, then in mid-spring, ends. Our
six-month predicted DST period is then unaffected by Ramadan for several
years as it moves through the winter months, before it is impinged upon
once again. In 2036–2038, it merely advances the end date by a few weeks
while Ramadan is in mid-autumn, but as it progresses forward, beginning in
2039, it is once again wholly within the late-April to late-October period,
and four transitions once again become necessary to reflect Egypt's past
practices.

Note that, just after tzdata 2016e was released a discussion was started as
to whether Egypt will actually observe all four transitions in years such
as 2017–2019 and 2039–2051, or whether they will choose to observe it only
on one side of the holy month or the other:
http://mm.icann.org/pipermail/tz/2016-June/023801.html

We don't yet know anything for sure about how this will be handled, though…
so from historical evidence, this remains our best guess for now.

--
Tim Parenti
sent from my Android phone
On 16 Jun 2016 10:53, "Dave Rolsky" <autarch at urth.org> wrote:

> On Thu, 16 Jun 2016, Dave Rolsky wrote:
>
> Here's a snippet of "zdump -v Africa/Cairo" with the latest changes:
>>
>
> I then realized I hadn't installed the latest tzcode. However, even with
> the latest version I still see 3 changes per year in Africa/Cairo starting
> in 2039.
>
> Is that really what's intended?
>
>
> Cheers,
>
> -dave
>
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