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Asia/Ishigaki?
by Hideyuki Suzuki Nov. 9, 1998

Nov. 9, 1998

In tzdata1998i.tar.gz, I found that two timezones are defined for Japan. This is somewhat strange to me, because only JST (+0900) is used everywhere in Japan including Ishigaki island. I want to suggest that Asia/Ishigaki (CST, +0800) zone should be removed. However, you may wonder why it was added to the database, and in tzarchive I found the following comment: Date: Tue, 3 Sep 1996 17:14:22 -0700 From: Paul Eggert <eggert(a)twinsun.com> Subject: proposed patch for selecting TZ, MET->CST, Sri Lanka, Antarctica,... > Asia/Ishigaki - uncomment it, since it seems to be right I don't know whether the zone was added at this time, but I suspect that it was added because of an ambiguous reason. So, I believe that it should be removed. I'm not on the tz list, so please leave my address in Cc: line when you reply. Thanks. -- hideyuki

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BUG: Solaris mktime with multiple timezones
by Scott Harrington Nov. 6, 1998

Nov. 6, 1998

I have posted the attached message to comp.unix.solaris, so replies should probably be posted there. I wanted to notify this mailing list since the bug affects those who use multiple time zones in their programs. -------- Original Message -------- Subject: BUG: Solaris mktime with multiple timezones Date: Fri, 06 Nov 1998 18:09:17 +0000 From: Scott Harrington <seh4(a)ix.netcom.com> Newsgroups: comp.unix.solaris I have uncovered a bug in the mktime() routine found in libc.so.1 and libc.a on my SunOS 5.5.1 Generic_103640-12 sun4u sparc SUNW,Ultra-2 machine: -rw-r--r-- 1 bin bin 1155756 Jun 23 1997 /usr/lib/libc.a -rwxr-xr-x 1 bin bin 664760 Jun 23 1997 /usr/lib/libc.so.1 The error is that mktime() returns WRONG values when you're switching between multiple time zones in a single program. I have attached a small program which should determine if your system has the bug or not. I make a mktime call in GB timezone, and then in GMT timezone. The second lookup returns incorrect values. If you have the bug, your output will be: TZ=GB 892162800 0 0 0 10 3 98 5 99 1 should be TZ=GB 892162800 0 0 0 10 3 98 5 99 1 TZ=GMT 892162800 0 0 23 9 3 98 4 98 0 should be TZ=GMT 892166400 0 0 0 10 3 98 5 99 0 On systems which implement mktime correctly, the output will be: TZ=GB 892162800 0 0 0 10 3 98 5 99 1 should be TZ=GB 892162800 0 0 0 10 3 98 5 99 1 TZ=GMT 892166400 0 0 0 10 3 98 5 99 0 should be TZ=GMT 892166400 0 0 0 10 3 98 5 99 0 I am curious to find out on which systems this bug exists. (2.6? /opt/SUNWspro/lib/libc.so.1?) The public Sunsolve patch list apropos 'libc' only led me to patch 103612-46 (I already had 103612-30) and applying this patch did not fix the problem. I have a crude LD_PRELOAD workaround (using the implementation of mktime from GNU glibc-2.0.7) for existing executables, if anyone is interested let me know and I will mail it or post it to this newsgroup. #include <time.h> #include <stdio.h> #include <stdlib.h> int main(int argc, char **argv) { time_t t; { struct tm tmBuf = {0, 0, 0, 10, 3, 98, 0, 0, -1}; putenv("TZ=GB"); t = mktime(&tmBuf); printf("TZ=GB %ld %d %d %d %d %d %d %d %d %d", t, tmBuf.tm_sec, tmBuf.tm_min, tmBuf.tm_hour, tmBuf.tm_mday, tmBuf.tm_mon, tmBuf.tm_year, tmBuf.tm_wday, tmBuf.tm_yday, tmBuf.tm_isdst); printf(" should be\n"); printf("TZ=GB 892162800 0 0 0 10 3 98 5 99 1\n"); } printf("\n"); { struct tm tmBuf = {0, 0, 0, 10, 3, 98, 0, 0, -1}; putenv("TZ=GMT"); t = mktime(&tmBuf); printf("TZ=GMT %ld %d %d %d %d %d %d %d %d %d", t, tmBuf.tm_sec, tmBuf.tm_min, tmBuf.tm_hour, tmBuf.tm_mday, tmBuf.tm_mon, tmBuf.tm_year, tmBuf.tm_wday, tmBuf.tm_yday, tmBuf.tm_isdst); printf(" should be\n"); printf("TZ=GMT 892166400 0 0 0 10 3 98 5 99 0\n"); } exit(0); }

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Re: new time conversion interface
by Nathan Myers Nov. 5, 1998

Nov. 5, 1998

Paul Hill wrote: > Nathan Myers wrote: > > > We're dealing with _humans_, here. It's a reasonable goal to try to > > increase the reliability of time entries by noting likely errors. > > ... > > A note that the time changed recently is *extremely* helpful when > > getting confirmation of a time entry, but most programmers are not > > equipped or inclined to root about in a transition database, > > Why would a programmer want to? To minimize mistakes. Any relevant information the system has that the user doesn't is a lost opportunity. People are not (uniformly) stupid, and can respond usefully to a notification that an entered time is dubious. Likewise, a logged timestamp annotated with reasons to doubt it may be more useful than a bare timestamp. The conversion function has discovered the information, the calling program is equipped to decide if it's useful. > The programmer asked to please > convert the fields into a timestamp given the TZ provided. I don't > see how going to look for other transition rules has anything to > do with it. There is still a list of possible interpretations > given just one possible fully accurate TZ definition. Current conversion functions don't report a list of possible interpretations, they report just one. That's what I'd like to fix in this interface. > Going looking > in a transition DB only provides more entries for the list returned > (An additional entry might capture a possible alternate based on > the possibility that the programmer really did not pass the library > the right TZ, because the library code can see that the given rules > did not apply on the date provided in the time struct.) The point is that the conversion function has just looked up all the relevant entries. It can discard any additional information it has gathered, or report it. The caller is equipped to choose which of the additional information is useful, but only if it's reported. > > I agree that the two examples are too similar. Originally I had > > #0 as the canonical "certain" time, and then realized that (as > > you noted) that condition is rare. At some point the likelihood > > of an error due to a transition becomes smaller than that of a > > simple typo, which can only be determined empirically. > > So how are you going to put that fuzzy set in the library code so > that sometimes you can return a "doubtful subsitution" and sometimes > you can return a "possible unofficial time"? Maybe instead of a "doubtful/possible" flag it just reports how long before the reported time the last transition occurred, and what the conversion would be if that one was missed. > > > Speaking of ambiguity, could you explain what your are really trying > > > to capture in #1 and #2, because your descriptions are of the same > > > circumstance. > > > > Er, that's a typo. ... > > > > The intended entry for #2 was 03:30. This is a valid "official" > > time, unlike 02:30. However, it is very likely to be wrong. > > But that makes the #2 entry jibberish, if I rewrite it as [gibberish] > Maybe it should be: > 2. Spring ambiguity, enter 03:30, but that is so close to the > change time it is suspicious. > > It would seem you could do the discussion of favor and repost a > complete list of possible combinations and what kind of rules you > are going to use to put your tags on all of the different > interpretations. That might not be the best description of the goal. The goal is a way for the conversion function to report the circumstances of the conversion in a form that is easily interpreted for different purposes. In my posting I was too specific about what are still unresolved design issues. > > Cases that are identical as far as the program is concerned > > (time is an hour off because of a clock not reset) are quite > > different in how the user experiences them. > > "identical as far as the program is concerned", but you are trying > to return two different values from the "alternative" time. > ... > One has to ask: since you have 16 possible return flag combinations, > could you please explain why only 5 of them are covered in your > list (and I see only 2), and what is right or wrong about the other > 11, i.e. "doubtful ... unofficial" etc. If you only have 5, just > have one enum that lists them and not imply states that don't exist. It may be that one enum with five values, or with four values and a field for when the last time change happened, would be appropriate. Again, you have identified a danger of being too specific. What I posted was an (unfortunately confusing) example meant to lend some concreteness to the discussion. Can we agree that it's useful for the conversion function to report (also) the circumstances of the conversion? Then we can proceed to explore how to report those circumstances. Nathan Myers ncm(a)cantrip.org

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new time conversion interface
by ncm＠cantrip.org Nov. 5, 1998

Nov. 5, 1998

Apologies for following up my own posting, but I don't want to lose the thread here. I have edited the quoted text below for clarity. > > Nathan Myers wrote: > > > The problem with the mktime model is that conversions between civil > > > time and timestamps can result in 2, 1, or <1 valid conversions ... > > ... it's a rare wall clock, legal document, train schedule or > airline ticket that indicates UTC offset, and when it does it's > likely to be wrong, especially during the "interesting" times. > ... > The problem that normally arises is that someone enters a date/time > and I want a numeric real-time value. I distinguish the following > troublesome cases: > > 1. It's in spring and they enter 02:30, and that time doesn't exist, > but there's a good guess (e.g. equiv. to 03:30) for what > they probably meant. (There's a corresponding case for leap > seconds.) > 2. In spring they enter 03:30, which might be correct, but they might > well have meant 04:30 because they failed to reset their clock. > 3. In autumn, they enter 01:30; did they mean the first time it > happened that day or the second? Either is equally valid. > 4. (Also in autumn) If they enter 02:30, did they mean officially > 02:30, or did they mean the second 01:30? I believe that conversions should yield a struct containing a reference timestamp, followed by up to four offsets tagged with official wall-clock offset, interpretation, and confidence values. For example, in the cases above, and ignoring leap seconds for the moment, we would get 0. Unambiguous time, e.g. 04:30 morning of a time change t0=123456789 offset 0: 0 sec; wall-clock offset: -3600 sec; interpretation: unambiguous; confidence: certain offset 0: -3600 sec; wall-clock offset: -3600 sec. interpretation: suggested substitute; confidence: doubtful 1. Spring ambiguity, enter 02:30 when it doesn't exist because civil time proceeded 01:59:59 -> 03:00:00. (Or 02:00:00 to 03:00:01? I don't know.) t0=123456789 offset 0: 0 sec; wall-clock offset: -3600 sec. interpretation: suggested substitute; confidence: doubtful 2. Spring ambiguity, enter 02:30 when it doesn't exist because civil time proceeded 01:59:59 -> 03:00:00 (or whatever). t0=123456789 offset 0: 0 sec; wall-clock offset: 0 sec. interpretation: official choice; confidence: Nominally unambiguous offset 1: -3600 sec; wall-clock offset: 0 sec. interpretation: suggested substitute; confidence: doubtful 3. Autumn ambiguity, enter 01:30 on morning when civil time proceeds from 01:59:59 to 01:00; is it the first or second 01:30 event? t0=123456789 offset 0: 0 sec; wall-clock offset: 3600 sec. interpretation: ambiguous choice; confidence: equal alternative offset 1: 3600 sec; wall-clock offset: 0 sec. interpretation: ambiguous choice; confidence: equal alternative 4. Autumn, enter 02:30, same morning as above; did they mean the official 02:30, or did they mean the second 01:30 because they failed to reset their clock? t0=123456789 offset 0: 0 sec; wall-clock offset: 0 sec. interpretation: official choice; confidence: Nominally unambiguous offset 1: 3600 sec; wall-clock offset: 0 sec. interpretation: unofficial choice; confidence: Possible alternative For each case above one might have up to two more entries corresponding to leap-second ambiguities. The detailed semantics of all the possible "interpretation" and "confidence" tags must be nailed down. This might end up looking sort of like the following C struct layout, using deliberately unsatisfactory names for exposition: typedef ... time_stamp; /* something more-or-less numeric */ typedef enum { official, unofficial, ambiguous, suggested } time_meaning; typedef enum { nominal, alternative, possible, doubtful } time_confidence; struct time_interpretation { int offset; /* limited to +/- 3601 */ long wall_offset; /* limited to +/- 43200 */ time_meaning meaning; time_confidence confidence; }; struct time_from_civil { time_stamp reference_time; int interpretation_count; /* range 0-4 */ time_interpretation interpretation[4]; }; (I've neglected leap-second ambiguity interpretations because they would reduce the clarity of the exposition.) The conversion function might look like: int time_convert(const struct tm *, const time_zone *, time_from_civil *); I think an interface like this would encapsulate knowledge about time conversion issues, exposing a high-level view of the possible real-time values implied by wall-clock time records. I think it would lead to better, more robust interfaces for conversions, and reduce programmer errors. Comments? Nathan Myers ncm(a)cantrip.org

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news from Estonia
by peter＠aldie.co.uk Nov. 4, 1998

Nov. 4, 1998

My relative in Estonia reports a rather confused picture. The law is clear enough: this year they changed to the EU rule time of 01:00 UTC from their previous midnight UTC. This is a change from 04:00 -> 03:00 local time. The newspapers didn't catch up though. They were still saying it was a change from 03:00 -> 02:00 local time. They can perhaps be forgiven for this as the new law was only dated 22 September. This spring in the UK the Times (a supposed `newspaper of record') printed a picture of a clock showing it going from 02:00 to 03:00. We haven't done that since 1980. The Estonian law can be found at: http://trip.rk.ee/cgi-bin/thw?${BASE}=akt&${OOHTML}=rtd&TA=1998&TO=1&AN=1390 Knowing my poor grasp of Estonian he offers the following free translation: According to the association agreement between the EU and the Republic of Estonia ratified by the Estonian law (RT II 1995, 22--27, 120) and in accordance with the 8th directive of EU 22. July 1997, 97/44/EU (EUT L 206, 1.08.1997, pp 62--63) the Government of Estonia decides to change to Summer Time as follows 1) start 3.00 by the zone time (1.00 GMT) on last sunday of March changing to 4.00; 2) end 4.00 by the zone time (1.00 GMT) on last sunday of October changing to 3.00) I also asked him whether they use any standard abbreviation for their standard and summer times. He says no, they use "suveaeg" (summer time) and "talveaeg" (winter time). He says there is still some discussion about whether they should continue fiddling with the clocks but didn't provide any specifics. Most Estonian newspapers have web pages linked from http://www.ee/www/Media/Journalism/Newspapers/welcome.html. The papers' pages are nearly all in Estonian only so I can't offer any more clues. Finally, this just confirms the existing data. No change is needed to the europe file. Peter Ilieve peter(a)aldie.co.uk

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Re: new time conversion interface
by Ian Tragen Nov. 3, 1998

Nov. 3, 1998

> long wall_offset; /* limited to +/- 43200 */ > Re. the above - I may have missed something here but if you restrict the offset to +/-12 hours, you would run into difficulties with New Zealand DST which is UTC+13h. Ian Tragen -- World Clock Page:- http://www.page-1.com/time

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Time Zone Converter
by Carroll, Nancy Oct. 30, 1998

Oct. 30, 1998

To Whom it May Concern, I am writing on behalf of Manitoba Trade with respect to your database of information used to operate a time zone converter. I am working on reconstruction of our website and in particular the method of constructing a time zone converter. Do you have any sort of licensing arrangement with respect to the use of your database? Do you allow your database to be used by outside sources? Could you please forward details of the nature of your operations and whether there is any way that we might be able to draw on your database of information for our time zone utility? Thank you very much for considering my inquiry. Sincerely, Nancy Carroll Manitoba Trade

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timezone database
by Roy Valdehueza Oct. 27, 1998

Oct. 27, 1998

Dear TZ, i'm glad you guys are around. If you don't mind though i'd like to ask which file on your ftp site am i going to download if i need a timezone database? And what database format is this? How is it used (or at least you can give me which file will give me the mechanics or algorithm to use this database)? Thanx a lot and advance merry Christmas! Gratefully yours, roy valdehueza

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new C time interface
by Nathan Myers Oct. 24, 1998

Oct. 24, 1998

[apologies if this has been seen before.] Part of the problem with struct tm/time_t is that it works ok for inode times but not for other equally-important uses. The problem with the mktime model is that conversions between civil time and timestamps can result in 2, 1, or <1 valid conversions, and neither the user (before the conversion) nor the library is equipped to favor one result over another, or deal properly with nonexistent times. mktime offers no interface for the algorithm to report what it finds, so it must falsify its results. I hope that any interface offered to improve on mktime will expose the information needed to write reliable code. If it is also "nice" for the common ranges where there actually is a one-to-one mapping, that's a bonus, but correctness should come first. Nathan Myers ncm(a)cantrip.org http://www.cantrip.org/

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Re: new C time interface
by INFOMAN Inc. Oct. 23, 1998

Oct. 23, 1998

I tend to agree with Nathan's remarks on for new C time interface. The issue, i.e. need for, correctness in conversions and linkages between (local) civil times and timestamps is one that is also raised in the context of e-commerce and e-business and needs to be resolved. Jake Knoppers <mpereira(a)istar.ca>

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