[tz] Error in Scandinavian tz data

Stephen Colebourne scolebourne at joda.org
Tue Jun 27 08:35:20 UTC 2023

On Tue, 27 Jun 2023 at 08:20, Magnus Fromreide via tz <tz at iana.org> wrote:
> On Sat, Jun 17, 2023 at 08:20:53PM +0200, Anders Rosendahl via tz wrote:
> Other people have, just like you, said that this is a bad move and this have
> lead to a fork of the project but I do not remember where that is located,
> this fork is used in at least some of the BSDs.


I don't want to maintain the fork, but I have no choice given the
current situation at IANA tzdb is simply broken as the OP notes.

> My personal opinion is that the default IANA build should say nothing about
> dates before 1970-01-01 - it should, in particular, not claim that changes
> for some random place (like Berlin) applies to some other place (like
> Copenhagen).

Indeed, this would be an acceptable and equitable outcome. It isn't
ideal, as TZDB actually holds the data for pre-1970, but at least the
pre-1970 data would be equally wrong everywhere, rather than favouring
some places over others (which is my primary objection).

On Tue, 27 Jun 2023 at 08:31, Guy Harris via tz <tz at iana.org> wrote:
> (At this point, I wish we could get away with doing as Microsoft do, and just return -1 for all attempts to call localtime() for dates prior to the UNIX Epoch.)

The simplest approach would be to determine a rule, eg.
 - take the standard offset that applied on most days (modal average)
for the 5 years from 1970 to 1975 - and use that pre-1970.
- or, take the LMT of the city and round to the nearest hour
So long as the answer is reasonable for most cases, it would be fine.


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