EUAsia rule glitch?

[Jesper Norgaard Welen]

I have found an application of the rule EUAsia for Azerbaijan, which
results in DST for Azerbaijan since 01-Jan-1996 which doesn't seem
logical, and does not follow common sense. I don't have a version of
zdump here, but use JodaTime, a package that uses tz database directly
to produce the tz transitions. Jodatime reports the following
transitions for Baku for 1996:

UTC: 1995-12-31T19:59:59.000Z, Asia/Baku: 1995-12-31T23:59:59.000+04:00
UTC: 1995-12-31T20:00:00.000Z, Asia/Baku: 1996-01-01T01:00:00.000+05:00
UTC: 1996-10-27T00:59:59.000Z, Asia/Baku: 1996-10-27T05:59:59.000+05:00
UTC: 1996-10-27T01:00:00.000Z, Asia/Baku: 1996-10-27T05:00:00.000+04:00

This is based on the following tz database definition:

Zone	Asia/Baku	3:19:24 -	LMT	1924 May  2
			3:00	-	BAKT	1957 Mar    # Baku Time
			4:00 RussiaAsia BAK%sT	1991 Mar 31 2:00s
			3:00	1:00	BAKST	1991 Aug 30 #
independence
			3:00 RussiaAsia	AZ%sT	1992 Sep lastSat 23:00
			4:00	-	AZT	1996 # Azerbaijan time
			4:00	EUAsia	AZ%sT	1997
			4:00	Azer	AZ%sT

The EUAsia rule looks like this:

# These rules are stolen from the `europe' file.
# Rule	NAME	FROM	TO	TYPE	IN	ON	AT	SAVE
LETTER/S
Rule	EUAsia	1981	max	-	Mar	lastSun	 1:00u	1:00
S
Rule	EUAsia	1996	max	-	Oct	lastSun	 1:00u	0
-

As you can see above, the intention was simply to copy EU rules to the
'asia' file so as to use the same logic (because the asia file can't see
the europe file). However, the above implementation is a cut-down
version of EU rule, where the logic is presumably that we only need
rules for 1996 and beyond. This has the side effect that DST in the
EUAsia rule is applied Last Sunday of March 1981 and maintained
unaltered until Last Sunday of October 1996. The error is that DST was
(probably) not observed from 01-Jan-1996 to Last Sunday of March 1996,
although I don't have authoritative information about this.

I therefore suggest the following change:

# These rules are stolen from the `europe' file.
# Rule	NAME	FROM	TO	TYPE	IN	ON	AT	SAVE
LETTER/S
Rule	EUAsia	1981	max	-	Mar	lastSun	 1:00u	1:00
S
+Rule	EUAsia	1979	1995	-	Sep	lastSun	 1:00u	0
-
Rule	EUAsia	1996	max	-	Oct	lastSun	 1:00u	0
-

This will give EUAsia rule the expected behavior right from 1981, with
DST transitions equivalent to the EU rule.

Regards, Jesper

Jesper Nørgaard Welen
Email: jnorgard at Prodigy.Net.mx	
Project Leader (Líder de Proyecto) Software
CIMMYT  -  Centro Internacional de Mejoramiento de Maíz y Trigo
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