Time zone confusion and implementation hints

Bill Seymour stdbill.h at pobox.com
Tue Jul 6 08:58:42 UTC 2010

On Mon, Jul 5, 2010 at 9:06 PM, Robert Elz <kre at munnari.oz.au> wrote:
> The other representation is the zic output - that's simple, and in a format
> that is essentially never going to change in any incompatible way, as that's
> the format that software everywhere is reading to actually convert times
> between UTC and local time (both directions) - and because its format already
> allows for everything (being so simple).

Almost, but not quite.  There are two things that I think are wrong with
the zic output:

- There's just a boolean indicating /whether/ we're observing some
   kind of advanced time (usually, but not necessarily, summer time,
   a.k.a., daylight saving time).  There's no way to recover the standard
   offset from UTC from a single entry.  You have to backtrack to the
   most recent entry for standard time and hope that it hasn't changed
   since then.

- Multi-byte integers are aligned on arbitrary byte boundaries.
   This can be a hassle on systems that require stricter alignment.
   (This isn't a fundamental loss of data like the DST switch is,
   just a pain in the rear.)

--Bill Seymour

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