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Re: FW: timelocal() discrepancy vs DateTime->epoch

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From:
Bill Ricker
Date:
March 16, 2017 11:47
Subject:
Re: FW: timelocal() discrepancy vs DateTime->epoch
Message ID:
CAAbKA3URhVqfeWSFhDRDiiR+6J6ufKOx-MPqSWKfF5tPpn_WnQ@mail.gmail.com
> I'm pretty sure timelocal() is wrong here, though I'm not sure why. There
> was no DST transition in that zone in 1910. In fact, there wasn't really a
> time zone until 1918. The pre-1918 zone file in the Olson database is just
> using local solar time, but it's not very meaningful. If you really care
> about local times in the early 1900s you probably need to calculate the
> solar noon for the given lat/long.

This is likely to be a Y2K/19100 window wrap issue.

The little dst.pl script that I use to check Olson DB -- used in 2007
to diagnose which servers needed Olson/TZ DB update -- also reports
DST transitions for 2010 when asked for 1910.
[ i think i grabbed it from blogs.perl.org and enhanced it ? no
authorship is noted ]

$ dst.pl -y 1910
Sun Mar 14 01:59:59 EST 2010 --> Sun Mar 14 03:00:00 EDT 2010
Sun Nov 07 01:59:59 EDT 2010 --> Sun Nov 07 01:00:00 EST 2010

(That script uses localtime(), Time::Local and POSIX qw(strftime), but
not DateTime.)

Supporting evidence -- Early November DST transition was novel in 2007.
(Giving the little trick-or-treaters the extra hour of daylight at
Hallowe'en was obviously desirable for decades, but it took until 2007
to get it done.)

I predict Lu's script will report DST transitions morning of Apr 2
and Oct 29 in 1906, since those were the dates in 2006.

-- 
Bill Ricker
bill.n1vux@gmail.com
https://www.linkedin.com/in/n1vux

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