[tz] Adding verified historic details

Guy Harris guy at alum.mit.edu
Wed Sep 4 21:27:51 UTC 2013

On Sep 4, 2013, at 2:15 PM, Lester Caine <lester at lsces.co.uk> wrote:

> If you want a 1970+ only database then it should be advertised as that,

As far as I know, he wants the ability for packagers of the database to create, from the tzdb, 1970+-only databases if they deem pre-1970 data not worth keeping, not to permanently expunge pre-1970 differences from the tzdb itself.  

> and we can create a second one which has all of time

If we're not going to be adding new tzids by splitting zones that differ only pre-1970, and there are currently tzids that cover a single region that has different pre-1970 behavior in different parts of the region, we're not going to have "a second one that has all of time" accurately.

> any distribution and API should be using the full range, just as their calendar should be accurate for historic dates.

Any distribution and API has the option to use whatever they choose; some particular UN*X might well themselves choose to merge tzids that differ only pre-1970.  That's not for us to dictate.  (Heck, as somebody noted, QNX has an *unsigned* seconds-since-the-Epoch time_t, so it's literally *impossible* to specify a pre-January 1, 1970, 00:00:00 UTC date as a time_t in QNX, so anything in QNX that use the tzdb to convert time_t's will never look at the pre-1970 data in the tzdb.)

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