[tz] tzfiles contain Unix epoch for the first transition time

[Paul Eggert]

Eric Erhardt wrote:
> I've hit a snag with the latest tzdata 2015f.  (I'm not sure when this change started, but the problem doesn't occur with the tzfiles that are shipped with an Ubuntu 14.04 distribution.)
> The problem is that the 2015f version of the tzdata contains an initial "Transition Time" that is out of order. The beginning of the America/Chicago tzfile looks like the following:
> Transition Time
>
> Transition Offset
>
> 01/01/1970 00:00:00
>
> -05:50:36
>
> 11/18/1883 18:00:00
>
> -06:00:00

That's not what I'm seeing.  I assume you're talking about the 64-bit part of 
the file, since the 1883 time stamp does not fit in 32 bits.  The first 
transition I see, at offset 1348 of the America/Chicago file, is for 
-576460752303423488 (0xf800000000000000), which is the BIG_BANG time (see 
zic.c).  The second, at file offset 1356, is for -2717650800 
(0xffffffff5e03f090), which is 1883-11-18 17:00:00 UTC.  Neither of these 
transition times agree with the times you're showing.

> the problem doesn't occur with the tzfiles that are shipped with an Ubuntu 14.04 distribution.)

For what it's worth, the America/Chicago file that I generate by typing 'make 
install' with the tz distribution is byte-for-byte identical to 
/usr/share/zoneinfo/America/Chicago on my 64-bit Ubuntu 15.04 host.

If I had to guess, my guess is that your software is mishandling the BIG_BANG 
time because the time stamp is so far in the past.  Perhaps Ubuntu 14.04 didn't 
do the Big Bang?