tzdata isstd question
All, Given the following zone: Zone America/Atikokan -6:06:28 - LMT 1895 -6:00 Canada C%sT 1940 Sep 29 -6:00 1:00 CDT 1942 Feb 9 2:00s -6:00 Canada C%sT 1945 Sep 30 2:00 -5:00 - EST I'm wondering why the transition on Feb 9, 1942 isn't flagged as being observed at standard time in the compiled tzfile. Does the time suffix in UNTIL not get applied to the following transition? -- Kenneth Murchison Principal Systems Software Engineer Carnegie Mellon University
On 10/29/2015 12:53 PM, Ken Murchison wrote:
Zone America/Atikokan -6:06:28 - LMT 1895 -6:00 Canada C%sT 1940 Sep 29 -6:00 1:00 CDT 1942 Feb 9 2:00s -6:00 Canada C%sT 1945 Sep 30 2:00 -5:00 - EST
I'm wondering why the transition on Feb 9, 1942 isn't flagged as being observed at standard time in the compiled tzfile.
Sorry, I must be missing something, but I am not following the question. For that absolute transition, there's no difference between 02:00 standard time, 03:00 local time, and 08:00 UTC; they're all the same thing, and the "s" in "2:00s" is purely for convenience in the source data.
On Thu, Oct 29, 2015, at 16:14, Paul Eggert wrote:
Sorry, I must be missing something, but I am not following the question. For that absolute transition, there's no difference between 02:00 standard time, 03:00 local time, and 08:00 UTC; they're all the same thing, and the "s" in "2:00s" is purely for convenience in the source data.
The binary data does include information about the difference for the purpose of determining how the transition should be treated if the timezone is transposed to a different offset due to being used as the basis for interpreting POSIX rules. This data is in the sections which tzh_ttisgmtcnt/tzh_ttisstdcnt determines the size of.
My message disappeared. I've determined this was because I changed my primary email address and wasn't recognized as subscribed to the list, but it would have been nice to have received a notification of this as I have for other lists. On Thu, Oct 29, 2015, at 16:14, Paul Eggert wrote:
Sorry, I must be missing something, but I am not following the question. For that absolute transition, there's no difference between 02:00 standard time, 03:00 local time, and 08:00 UTC; they're all the same thing, and the "s" in "2:00s" is purely for convenience in the source data.
The binary data does include information about the difference for the purpose of determining how the transition should be treated if the timezone is transposed to a different offset due to being used as the basis for interpreting POSIX rules. This data is in the sections which tzh_ttisgmtcnt/tzh_ttisstdcnt determines the size of.
On 10/30/2015 01:42 PM, Random832 wrote:
My message disappeared. I've determined this was because I changed my primary email address and wasn't recognized as subscribed to the list, but it would have been nice to have received a notification of this as I have for other lists.
On Thu, Oct 29, 2015, at 16:14, Paul Eggert wrote:
Sorry, I must be missing something, but I am not following the question. For that absolute transition, there's no difference between 02:00 standard time, 03:00 local time, and 08:00 UTC; they're all the same thing, and the "s" in "2:00s" is purely for convenience in the source data. The binary data does include information about the difference for the purpose of determining how the transition should be treated if the timezone is transposed to a different offset due to being used as the basis for interpreting POSIX rules.
This data is in the sections which tzh_ttisgmtcnt/tzh_ttisstdcnt determines the size of.
Right. Is this info actually used in practice? If not, then I probably don't care. Anyhow, back to my original question, I still don't understand why zic doesn't flag the Feb 9, 1942 transition as being observed at standard time. Zone America/Atikokan -6:06:28 - LMT 1895 -6:00 Canada C%sT 1940 Sep 29 -6:00 1:00 CDT 1942 Feb 9 2:00s -6:00 Canada C%sT 1945 Sep 30 2:00 -5:00 - EST As part of my tzdist server, I've written code to translate iCalendar VTIMEZONE data back into tzfile format, and the only place that my files differ from files compiled with zic are those indicators in which an UNTIL time has a non-wall time suffix. All my transition times and other indicators match. For the zone above I have the ttisstd bit set in my data for the Feb 9, 1942 transition. zic (2015g) does not set this bit. -- Kenneth Murchison Principal Systems Software Engineer Carnegie Mellon University
On 2015-10-30 11:52, Ken Murchison wrote:
On 10/30/2015 01:42 PM, Random832 wrote:
My message disappeared. I've determined this was because I changed my primary email address and wasn't recognized as subscribed to the list, but it would have been nice to have received a notification of this as I have for other lists.
On Thu, Oct 29, 2015, at 16:14, Paul Eggert wrote:
Sorry, I must be missing something, but I am not following the question. For that absolute transition, there's no difference between 02:00 standard time, 03:00 local time, and 08:00 UTC; they're all the same thing, and the "s" in "2:00s" is purely for convenience in the source data. The binary data does include information about the difference for the purpose of determining how the transition should be treated if the timezone is transposed to a different offset due to being used as the basis for interpreting POSIX rules.
This data is in the sections which tzh_ttisgmtcnt/tzh_ttisstdcnt determines the size of.
Right. Is this info actually used in practice? If not, then I probably don't care.
Anyhow, back to my original question, I still don't understand why zic doesn't flag the Feb 9, 1942 transition as being observed at standard time.
Zone America/Atikokan -6:06:28 - LMT 1895 -6:00 Canada C%sT 1940 Sep 29 -6:00 1:00 CDT 1942 Feb 9 2:00s -6:00 Canada C%sT 1945 Sep 30 2:00 -5:00 - EST
As part of my tzdist server, I've written code to translate iCalendar VTIMEZONE data back into tzfile format, and the only place that my files differ from files compiled with zic are those indicators in which an UNTIL time has a non-wall time suffix. All my transition times and other indicators match.
For the zone above I have the ttisstd bit set in my data for the Feb 9, 1942 transition. zic (2015g) does not set this bit.
Reformatting lightly and adding headings and emphasis, we can see that in 1942, that zone and rule both say that time zone observed saving time: War time == DST - standard time was not resumed until Sep 1945. # Zone NAME GMTOFF RULES/SAVE FORMAT [UNTIL] Zone America/Atikokan -6:06:28 - LMT 1895 -6:00 Canada C%sT 1940 Sep 29 -6:00 *1:00* CDT 1942 Feb 9 2:00s -6:00 Canada C%sT 1945 Sep 30 2:00 -5:00 - EST # Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S ... Rule Canada 1942 only - Feb 9 2:00 *1:00* W # War Rule Canada 1945 only - Aug 14 23:00u 1:00 P # Peace Rule Canada 1945 only - Sep 30 2:00 0 S ... The US rules say the same as above, although practice may have varied depending on whether the zones normally observed DST. The UK rules (GB-Eire) are similar, but summer time was observed from Feb 1940, and double summer time during the normal DST periods, only returning to GMT in Oct 1945. Similar practices may have been observed in other allied countries while unoccupied during WWII. -- Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada
participants (4)
-
Brian Inglis -
Ken Murchison -
Paul Eggert -
Random832