what on earth is firefox up to?

[Roberto Ragusa]

On 07/01/2012 04:20 PM, Tim wrote:

> On that note, I've often wondered how systems that look at a file's GMT
> datestamp and tell you that time translated into your local time, cope
> with datestamps from a long way away, when timezone rules keep on
> changing.  We could maintain a table of rules so that the computer can
> correctly give you the times during summer of 1976, but how far back is
> the table maintained?  Sure, you won't have to read back a timestamp
> from the year 1827, but there could be a reason to calculate something
> from a known date and time, that's not to do with a computer file.  And
> there's the converse function.  If you had to calculate a date and time
> in 2023, would you know what rules would be applied during that year to
> do it correctly?

We *do* have a table of rules, it is in the tzdata package.
You will be surprised by how much information is there.
For future dates, of course, there can be inaccuracies, as rules are
often changed. That is the reason tzdata.rpm is often updated.

Try
  "zdump Europe/Rome"
I see rules covering since 1866 up to 2500. Not bad (Italy was forged on 1861).

Maintaining the tzdata rules is quite a job.
Recently the maintainer retired and IANA had to prepare a "transition plan"
to handle the emergency:
  http://tech.slashdot.org/story/11/03/03/2143249/timezone-maintainer-retiring

Then there were guys claiming that the info is copyrighted:
  http://yro.slashdot.org/story/11/10/06/1743226/civil-suit-filed-involving-the-time-zone-database

(they then realized they were wrong).

Handling time is really complex, but some smart guys work on that.

-- 
   Roberto Ragusa    mail at robertoragusa.it