[tz] [tz-announce] 2018i release of tz code and data available

Tim Parenti tim at timtimeonline.com
Fri Jan 4 20:33:00 UTC 2019


On Fri, 4 Jan 2019 at 14:43, Deborah Goldsmith via tz <tz at iana.org> wrote:

> Here’s the (partial) diff of transitions that results from 2018i vs. 2018g
> (both generated from rearguard tarballs):
>
>  Africa/Casablanca  Sun Jun 17 01:59:59 2018 UTC = Sun Jun 17 01:59:59
> 2018 +00 isdst=0
>  Africa/Casablanca  Sun Jun 17 02:00:00 2018 UTC = Sun Jun 17 03:00:00
> 2018 +01 isdst=1
> -Africa/Casablanca  Fri Oct 26 22:59:59 2018 UTC = Fri Oct 26 23:59:59
> 2018 +01 isdst=1
> -Africa/Casablanca  Fri Oct 26 23:00:00 2018 UTC = Sat Oct 27 00:00:00
> 2018 +01 isdst=0
> -Africa/Casablanca  Mon Jan 18 03:14:07 2038 UTC = Mon Jan 18 04:14:07
> 2038 +01 isdst=0
> -Africa/Casablanca  Tue Jan 19 03:14:07 2038 UTC = Tue Jan 19 04:14:07
> 2038 +01 isdst=0
> +Africa/Casablanca  Sun May  5 01:59:59 2019 UTC = Sun May  5 02:59:59
> 2019 +01 isdst=1
> +Africa/Casablanca  Sun May  5 02:00:00 2019 UTC = Sun May  5 02:00:00
> 2019 +00 isdst=0
>
> Debbie


The issue seems to have been introduced in ziguard.awk at
https://github.com/eggert/tz/blob/8539a448ebc8897e40d62f16dc4d0ada3f07b3ca/ziguard.awk#L93-L96
in 8539a44
<https://github.com/eggert/tz/commit/8539a448ebc8897e40d62f16dc4d0ada3f07b3ca>,
which is causing the substitution.

Though I will admit it was not straightforward deriving the intent of that
substitution from the comments, it is there because the 2018-10-26
transition was NOT a transition in UT offset.  In a rearguard sense, 2018g
predicted that the new timezone of +01 would be permanent and thus switched
to +01 with rearguard isdst=0 on 2018-10-26.  As it is now expected that
Morocco will "fall back" to +00 each Ramadan, 2018h and 2018i consider
rearguard isdst to have instead remained 1 on 2018-10-26 (since there was
no clock change), and that the flag will become rearguard isdst=0 when the
clocks fall back each Ramadan.

(The vanguard format, by contrast, considers +01 the new "standard" time
effective 2018-10-26, which would show up as a transition from +01, isdst=1
to +01, isdst=0; and Ramadan is considered to have negative DST.)

So the diff you're seeing here, best I can tell, reflects expected behavior
and accurate data for Morocco in 2018h and 2018i.

--
Tim Parenti
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