[tz] UTC calculation for March 12, 3001 [IANA #1143241], [PR 9419866]

[Paul Goyette]

On Tue, 21 May 2019, Lasher, Beth wrote:

> In the year 3001, Daylight Savings time is applied on Sunday March 9, 
> 3001 as expected.  (Eastern Standard time).  BUT on the following 
> Thursday, March 12, 3001 at 3 am, it seems that another Daylight 
> Savings Time change is applied.  After March 12, 3001, the UTC time 
> zone offset for Eastern Daylight Savings Time is 3 hours (not 4) and 
> remains that way until the year 9999.  Is this correct?  What is the 
> cause of this second time offset change?

Hmmm.  On my system, in the year 3001, March 8th is a Sunday, not March 
9th!

And with zdump I see no extra DST changes for either America/Los_Angeles 
or EST5EDT:

# zdump -vc 2999,3002 EST5EDT
EST5EDT  -9223372036854775808 = NULL
EST5EDT  -9223372036854689408 = NULL
EST5EDT  Sun Mar 10 06:59:59 2999 UT = Sun Mar 10 01:59:59 2999 EST isdst=0 gmtoff=-18000
EST5EDT  Sun Mar 10 07:00:00 2999 UT = Sun Mar 10 03:00:00 2999 EDT isdst=1 gmtoff=-14400
EST5EDT  Sun Nov  3 05:59:59 2999 UT = Sun Nov  3 01:59:59 2999 EDT isdst=1 gmtoff=-14400
EST5EDT  Sun Nov  3 06:00:00 2999 UT = Sun Nov  3 01:00:00 2999 EST isdst=0 gmtoff=-18000
EST5EDT  Sun Mar  9 06:59:59 3000 UT = Sun Mar  9 01:59:59 3000 EST isdst=0 gmtoff=-18000
EST5EDT  Sun Mar  9 07:00:00 3000 UT = Sun Mar  9 03:00:00 3000 EDT isdst=1 gmtoff=-14400
EST5EDT  Sun Nov  2 05:59:59 3000 UT = Sun Nov  2 01:59:59 3000 EDT isdst=1 gmtoff=-14400
EST5EDT  Sun Nov  2 06:00:00 3000 UT = Sun Nov  2 01:00:00 3000 EST isdst=0 gmtoff=-18000
EST5EDT  Sun Mar  8 06:59:59 3001 UT = Sun Mar  8 01:59:59 3001 EST isdst=0 gmtoff=-18000
EST5EDT  Sun Mar  8 07:00:00 3001 UT = Sun Mar  8 03:00:00 3001 EDT isdst=1 gmtoff=-14400
EST5EDT  Sun Nov  1 05:59:59 3001 UT = Sun Nov  1 01:59:59 3001 EDT isdst=1 gmtoff=-14400
EST5EDT  Sun Nov  1 06:00:00 3001 UT = Sun Nov  1 01:00:00 3001 EST isdst=0 gmtoff=-18000
EST5EDT  9223372036854689407 = NULL
EST5EDT  9223372036854775807 = NULL



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| Paul Goyette       | PGP Key fingerprint:     | E-mail addresses:     |
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