My confusion with Asia/Aqtau

[Dave Rolsky]

I'm trying to implement a parse/code generator based on the Olson DB
_text_ files (not binary).

I think I've got it mostly working, but there's some strange edge cases.
One of them involves Asia/Aqtau, and I'm trying to figure out if I'm
_really_ understanding what the file indicates.

The observances for this zone include the following:

 			5:00 RussiaAsia	AQT%sT	1995 Sep lastSun # Aqtau Time
 			4:00 RussiaAsia	AQT%sT

The RussiaAsia rules include the following rules which apply to those
observances:

 Rule RussiaAsia	1993	max	-	Mar	lastSun	 2:00s	1:00	S
 Rule RussiaAsia	1993	1995	-	Sep	lastSun	 2:00s	0	-
 Rule RussiaAsia	1996	max	-	Oct	lastSun	 2:00s	0	-

By my reading, this indicates the following transitions:

* On Sep 24, 1995 at 00:00:00 _local_ time, the offset from UTC changes
from 05:00 to 04:00.  However, the DST rule is still in effect, so the
total offset goes from 06:00 to 05:00.

* On Sep 24, 1995 at 01:00:00 local time (2:00s == 1:00 wall when DST is
in effect), the rule changes so that DST is no longer in effect, and the
cumulative offset goes from 05:00 to 04:00.


Is this _really_ correct?  It seems awfully strange to have an observance
change so close to a DST change.  And if cases like these are possible,
it's really going to complicate my code.  But if it is correct, I do want
to get it right in my code.

OTOH, if it's wrong, and such things don't happen, I'd be just as happy to
leave me code as is ;)


-dave

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