[tz] Lack of "initial" transitions for some zones

Howard Hinnant howard.hinnant at gmail.com
Tue Jul 21 18:09:49 UTC 2015

On Jul 21, 2015, at 10:47 AM, Jon Skeet <skeet at pobox.com> wrote:
> I suspect this is just a matter of how the data has been specified, but it's a little odd...
> I'm looking at the output of zic for each zone, and almost all zones start with a "transition" for some timestamp in the long distant past - including fixed zones such as UTC and Etc/*.
> However, the legacy "root" zones of CET, EET, PST8PDT etc don't have this initial "transition" in the file - unless I'm misinterpreting it, which is always a possibility.
> Would it make sense to adjust either the data or zic to make all zic output (in the 8-byte-timestamp format, at least) cover all of time? I realize that this "extra" data (presumably an insertion of "standard time until the first transition") may well not be historically accurate - but I doubt that it would be any less accurate than other zones in a similar situation.

Just zeroing in on PST8PDT, it looks to me like its initial state (from the beginning of time) is unambiguously:

-08:00:00 standard PST

I get this by using:

Zone	PST8PDT		 -8:00	US	P%sT

And “falling off the beginning” of the US Rule list (by finding the first Rule with 0 save):

Rule	US	1918	1919	-	Oct	lastSun	2:00	0	S


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