On 11/05/18 23:32, Vlad Khorsun via Firebird-devel wrote:
12.05.2018 1:12, Lester Caine wrote:
On 11/05/18 20:37, Adriano dos Santos Fernandes wrote:
* PST is Pitcairn or Pacific, with the same offset, they are
considered different time zones
ICU data is derived from TZ data hosted by IANA
(http://site.icu-project.org/tznotice).
I really can't answer questions about specific time zones, but really
grateful if we can clarify them.
The abbreviations are not defined to be unique. Only a subset of them
can be used as identifiers, the rest are only 'defined' when
associated with a particular rule, so are only suitable for displaying.
Personally I need to see the different UK/Ireland timezone idents
giving the right offsets prior to 1970 and that depends on how the ICU
extract has been processed. It's not a case that 'the ICU data is
derived from TZ data', it also depends on how the TZ data is processed
by ICU and I'm not seeing ANY information on that. For the Irish area
we then get IST standing for Irish Summer Time prior to 1968, and
Irish Standard Time after that. Nothing is easy on any of this ... and
IST is used in a number of other rules with similar differences in
expansion. A quick scan of the ICU files would suggest 'IST' is used
by them for India Standard Time but it would be nice if there was an
easy way to confirm that? Certainly I'm not seeing data in
zoneinfo64.txt for Isle of man, Jersey, Guernsey or Belfast so I
suspect they are not valid pre-1970 :(
Probably, this answers on (some of) your questions
http://userguide.icu-project.org/datetime
http://userguide.icu-project.org/datetime/calendar
http://userguide.icu-project.org/datetime/timezone
There is no information on those pages covering just what way the base
TZ data is processed. I think it is probably safe to assume that it is
unusable for providing timezone offsets prior to 1970 which is the
current target of TZ itself, so it would be nice if there was a suitable
warning somewhere? But some way to restore the pre 1970 data would be
useful!
--
Lester Caine - G8HFL
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