[tz] zic bug: Wall-clock ordering of transition times

Brian Park brian at xparks.net
Thu Dec 31 19:22:18 UTC 2020

Got it, thanks for the clarification, it helps to have more context about
what you were thinking. I was focused on Grand_Turk, so probably simplified
my exposition too much. I think the better explanation is that the 2:00 in
the UNTIL field precisely matches the 2:00 in the AT in the US Rule, so
there is only one transition, instead of 2 transitions. Same thing seems to
happen with the 2:00s in the UNTIL for Kaliningrad, which matches the 2:00s
in the AT for the Russia Rule.

The thing that I was wondering was whether the semantics of the zone info
text files actually mandated a transition from 2:00 to 1:00 for Grand_Turk,
if the Zone entry was set to 2:00, instead of its current 3:00 value. Or
whether the special case in the zic compiler was an additional rule on top
of the normal semantics of the zone info text files, in order to parse the
Grand_Turk case properly. I managed to convince myself that the normal
rules of the text files were sufficient for Grand_Turk. And my parsing code
seems to implement those normal rules properly.

On Tue, Dec 29, 2020 at 4:11 PM Michael H Deckers <
michael.h.deckers at googlemail.com> wrote:

>      On 2020-12-29 22:45, Brian Park wrote:
> > Then I wish you had said exactly that, instead of having me go off on a
> > tangent.
>     So do I. I am sorry to have lead you astray.
> > Maybe I am misinterpreting something, but I don't understand why
> > you are being confrontational about this. I am presenting results from 2
> > different TZ parsers, using algorithms developed independently. I thought
> > this would be interesting and relevant to this topic.
>     I do not want to sound confrontational but I do
>     want to be short. My comment on your original post
>     concerned only one sentence, and I did in no way
>     comment on the rest of that post.
> >   I don't understand
> > the point that you are trying to make.
>     The complete sentence I commented about is:
>        The core of why it "just works" seems be in the interpretation
>        of the "2:00 transition to US Rule", and the fact that "2:00"
>        is Wall-time, not S-time or U-time:
>     I understand this to imply that a time of day value with
>     a postfix "s" or "u" in the UNTIL column would preclude
>     that it "just works".
>     Now there are cases where two transitions (an increase
>     in SAVE value after a decrease in STDOFF) are colaesced,
>     and where the corresponding UNTIL column has a time of
>     day value with a postfixed "s"; one example is for
>     Kaliningrad.
>     My comment asks how your code deals with such cases,
>     given that it would not "just work".
>     I hope this makes my point clear(er).
>     Michael Deckers.
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