Bug or feature?

Jesper Norgaard Welen jnorgard at prodigy.net.mx
Sun Jan 22 04:52:26 UTC 2006


This is truely mindboggling. I am just as baffled as Deborah Goldsmith.
only way I can explain this behavior of the software is if the rule of
second line is applied on the time of the first line, at the moment of
UNTIL for the first line, determining that isdst=1 and only then
GMT offset -6 of the second line. That is not very logical when reading
these 2 lines, and there is no documentation of this in e.g. zdump.8.txt
more relevant in zic.8.txt. However, if all the tz zone lines have been
with this "feature" then to change it to the more logical interpretation
of Deborah and me is not an easy task. But at least the documentation
be updated to clearly specify what happens in the process of a zone line

I would thus like to know what happens with the following similar

			-5:00	-	EST	2006 Apr  2 2:01
			-6:00	US	C%sT

Since the UNTIL time/date and the DST application in the US rule don't
coincide, I assume this would be the result:

1:59:59 EST
2:00:00 EST
2:00:59 EST
1:01:00 CST
1:59:59 CST
3:00:00 CDT

or is there another inheritance scheme taking place?

Jesper Nørgaard Welen

-----Original Message-----
From: Deborah Goldsmith [mailto:goldsmit at apple.com] 
Sent: Saturday, January 21, 2006 11:03
To: tz at lecserver.nci.nih.gov
Subject: Re: proposed tz patches for Indiana, New Brunswick, Gaza, etc.

On Jan 20, 2006, at 9:14 PM, Paul Eggert wrote:
> But my proposed rules do that.  "zdump -v America/Indiana/Knox" 
> outputs this for me:
>    ...
>    America/Indiana/Knox  Sun Apr  2 06:59:59 2006 UTC = Sun Apr  2
> 01:59:59 2006 EST isdst=0
>    America/Indiana/Knox  Sun Apr  2 07:00:00 2006 UTC = Sun Apr  2  
> 02:00:00 2006 CDT isdst=1
>    ...
> Are you getting different output from zdump?

I believe you, I just don't understand why -- it's my brain that's  
giving different output. :-) If 07:00:00 UTC is 01:00:00 CST in  
America/Chicago, why is it 02:00:00 CDT in America/Indiana/Knox, when  
America/Chicago has:

                         -6:00   US      C%sT

and America/Indiana/Knox also has:

                         -6:00   US      C%sT

Why is the same information interpreted differently in these two  
cases? Does the interpretation depend on the prior line? If so, is  
this an ambiguity in the specification?

I haven't tried this in ICU yet; I suspect it may interpret the rules  
differently than zdump. I'll check on Monday.


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