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Okay, now I have done my own investigations and found following
answer:<br>
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If the switch (expressed as UNTIL-time in a ZONE-line) is before any
dst-rule valid for given UNTIL-related year then we have to apply
the previous daylight saving offset valid at that time (previous
means before the switch). The southern hemisphere matters here, see
America/Argentina/Jujuy in 1992. However, there is one exception. If
there are no dst-rules at all in given year then we have to apply
zero-offset (consistent with Asia/Gaza for the 1967 switch). I
wished these tricky details were documented anywhere and I hope it
helps for anyone else.<br>
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<th align="RIGHT" nowrap="nowrap" valign="BASELINE">Betreff:
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<td>Re: [english 83%] Re: [tz] historic Oslo times</td>
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<th align="RIGHT" nowrap="nowrap" valign="BASELINE">Datum: </th>
<td>Sat, 07 Mar 2015 01:49:07 +0100</td>
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<th align="RIGHT" nowrap="nowrap" valign="BASELINE">Von: </th>
<td>Meno Hochschild <a class="moz-txt-link-rfc2396E" href="mailto:mhochschild@gmx.de"><mhochschild@gmx.de></a></td>
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<th align="RIGHT" nowrap="nowrap" valign="BASELINE">An: </th>
<td>Paul Eggert <a class="moz-txt-link-rfc2396E" href="mailto:eggert@cs.ucla.edu"><eggert@cs.ucla.edu></a></td>
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<pre>Thank you very much for clarification. Is this rule/algorithm/procedure
documented anywhere? So for Oslo we have a rule BEFORE the switch which
gives us the dst-offset of +01:00 to be applied.
And what will happen if the rule in question taking effect happens AFTER
the time of switch (as expressed in UNTIL-term) meaning: for given year
there is no rule before switch? Is it okay to assume daylight-savings
zero in this edge case? ls this assumption also valid for southern
hemisphere?
Am 06.03.2015 um 22:29 schrieb Paul Eggert:
> Meno Hochschild wrote:
>> The rule for 1940 cannot be applied because 1st of Apr is clearly
>> before the
>> UNTIL-date of zone line in question when changing from Norway-rule to
>> C-Eur-rule.
>
> When a zone switches from one set of rules to another, the rule in
> effect at the time of the switch is the rule that governs, even if
> this rule first took effect before the switch. So the rule you
> mention can be applied, and the data for Europe/Oslo should be OK.
> You can verify this by running the command "zdump -v Europe/Oslo" and
> verifying that all the transitions are as expected. Here are the
> war-year transitions that I observed that way:
>
> Sat Aug 10 21:59:59 1940 UT = Sat Aug 10 22:59:59 1940 CET isdst=0
> gmtoff=3600
> Sat Aug 10 22:00:00 1940 UT = Sun Aug 11 00:00:00 1940 CEST isdst=1
> gmtoff=7200
> Mon Nov 2 00:59:59 1942 UT = Mon Nov 2 02:59:59 1942 CEST isdst=1
> gmtoff=7200
> Mon Nov 2 01:00:00 1942 UT = Mon Nov 2 02:00:00 1942 CET isdst=0
> gmtoff=3600
> Mon Mar 29 00:59:59 1943 UT = Mon Mar 29 01:59:59 1943 CET isdst=0
> gmtoff=3600
> Mon Mar 29 01:00:00 1943 UT = Mon Mar 29 03:00:00 1943 CEST isdst=1
> gmtoff=7200
> Mon Oct 4 00:59:59 1943 UT = Mon Oct 4 02:59:59 1943 CEST isdst=1
> gmtoff=7200
> Mon Oct 4 01:00:00 1943 UT = Mon Oct 4 02:00:00 1943 CET isdst=0
> gmtoff=3600
> Mon Apr 3 00:59:59 1944 UT = Mon Apr 3 01:59:59 1944 CET isdst=0
> gmtoff=3600
> Mon Apr 3 01:00:00 1944 UT = Mon Apr 3 03:00:00 1944 CEST isdst=1
> gmtoff=7200
> Mon Oct 2 00:59:59 1944 UT = Mon Oct 2 02:59:59 1944 CEST isdst=1
> gmtoff=7200
> Mon Oct 2 01:00:00 1944 UT = Mon Oct 2 02:00:00 1944 CET isdst=0
> gmtoff=3600
> Mon Apr 2 00:59:59 1945 UT = Mon Apr 2 01:59:59 1945 CET isdst=0
> gmtoff=3600
> Mon Apr 2 01:00:00 1945 UT = Mon Apr 2 03:00:00 1945 CEST isdst=1
> gmtoff=7200
> Mon Oct 1 00:59:59 1945 UT = Mon Oct 1 02:59:59 1945 CEST isdst=1
> gmtoff=7200
> Mon Oct 1 01:00:00 1945 UT = Mon Oct 1 02:00:00 1945 CET isdst=0
> gmtoff=3600
>
>
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