- tz - lists.iana.org

FW: Barnaby
by Thom Hehl Nov. 8, 2011

Nov. 8, 2011

>You're using zone.tab as a canonical list of timezones, which it isn't. >zone.tab is only useful for selecting timezones via countries; for a >list of all timezones you can serve you should just look at the tzfiles. Did you read the readme? That is the next thing I'm going to fix. >Your usage of time_t is not appropriate. The type you want there is >dictated by the tzfile format, not by libc. The API needs to use time_t, so the usage is dictated by the use case, not by the tzfile, which is why it's appropriate. >You're doing a linear search (in transitionTimesIndex) that should really >be a binary search. Yeah, that can be optimized. The problem with doing a binary search is that you're not looking for an equal condition, but the smallest gap the thing you're looking for fits into. I'm aware that a binary search would improve performance some, but didn't devote time to it yet. Again, this is a beta drop designed to get the job done so I can move on with other priorities that pay money. :) >Overall it looks like you're interpreting (the 32-bit part of) the tzfile >correctly, but I find the code too messy to be sure. >You have some instance methods that should be class methods ("static"). >There is much else that is poor about your object model, but that's all >off topic for this list. Feel free to email me off list as you please for any improvements you might suggest. As I indicated in the read-me there is much room for improvement, but this meets my current needs. Open source is all about refining code over iterations, right? Whatever changes you'd like to suggest will be re-visited when I get some time to come back and work on this more. Thanks for the excellent feedback. -----Original Message----- From: Zefram [mailto:zefram@fysh.org] Sent: Tuesday, November 08, 2011 12:44 PM To: Thom Hehl Cc: tz(a)iana.org Subject: Re: [tz] Barnaby Thom Hehl wrote: >http://code.google.com/p/barnaby You're using zone.tab as a canonical list of timezones, which it isn't. zone.tab is only useful for selecting timezones via countries; for a list of all timezones you can serve you should just look at the tzfiles. Your usage of time_t is not appropriate. The type you want there is dictated by the tzfile format, not by libc. You're doing a linear search (in transitionTimesIndex) that should really be a binary search. Overall it looks like you're interpreting (the 32-bit part of) the tzfile correctly, but I find the code too messy to be sure. You have some instance methods that should be class methods ("static"). There is much else that is poor about your object model, but that's all off topic for this list. -zefram

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Decoding timezone data
by Thom Hehl Nov. 8, 2011

Nov. 8, 2011

OK, so I'm making some progress on my library. I'm attempting to read the timezone information for America/Kentucky/Louisville. When I run through the values for transition times, I get 177 values such as follows: 2661690496, 2693140096, 2759063296, ... The docs say these transition times are in values returned by the c time function, which returns seconds since midnight, 1/1/1970. If that is the case, then the three values above convert to: May 6, 2054 at 2:28:16 PM May 5, 2055 at 2:28:16 PM June 6, 2057 at 2:28:16 PM These are nowhere near the DST conversion dates for these years and are moving forward. This appears incorrect. Can someone show me what I'm doing wrong? Thanks.

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"Standard byte order"
by Thom Hehl Nov. 8, 2011

Nov. 8, 2011

I'm assuming that "Standard byte order" referred to over and over in the docs means Most Significant Byte first? It should really be documented that way. As far as I know, there is no standard byte order.

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Re: [tz] Australian time zone abbreviations
by Shaun Bouckaert Nov. 8, 2011

Nov. 8, 2011

On 6 November 2011 20:51, Eric Ulevik <eulevik(a)gmail.com> wrote: > On Sun, Nov 6, 2011 at 9:20 PM, Shaun Bouckaert > <shaun.bouckaert(a)gmail.com> wrote: > [snip]> http://australia.gov.au/about-australia/our-country/time > [snip]> I believe that the abbreviations used on the federal > government> website should be used. > Time zones in Australia are legislated by acts of state governments, > not the federal government. The acts mostly refer to "summer time" and > "standard time". > > Eg. South Australia: > http://www.austlii.edu.au/au/legis/sa/consol_act/dsa1971165/ > > Regards, > > Eric Ulevik > In the absence of any specific mention in the state legislation of an appropriate abbreviation, and considering the timezones and their abbreviations span multiple states, I see no reason why federal government documentation on the matter shouldn't be recognised, especially considering the only basis for the current system is a couple of AltaVista searches and the opinion of Australian's on the list at the time. Shaun Bouckaert

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Russian TZ Samara has no offset listed since 2010g
by manprsi2 Nov. 7, 2011

Nov. 7, 2011

Hello, Europe/Samara has the follow zone.tab definition since 2010g (no offset listed) RU +5312+05009 Europe/Samara Moscow - Samara, Udmurtia It used to be RU +5312+05009 Europe/Samara Moscow+01 - Samara, Udmurtia Samara changed to Moscow but all the other regions are listed with an offset even if +00 (Volgograd, Moscow) while Samara is not. I can not tell by searching the mail archive if the change this way was intentional or not? Thanks - Manpreet

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Australian time zone abbreviations
by Shaun Bouckaert Nov. 6, 2011

Nov. 6, 2011

Having long been irked by the fact that the abbreviation for Brisbane is EST, as opposed to AEST, I read through the time zone data file and found that the reason for this was a discussion back in 2001. I'm not sure if this existed then, but there is a federal government web page that lists the time zones and their abbreviations. http://australia.gov.au/about-australia/our-country/time ================================================================================ Time zones With a land mass close to 7.7 million square kilometres, Australia is the world’s sixth largest country and is divided into three separate time zones. Australian Eastern Standard Time (AEST) Covers the eastern states of Queensland, New South Wales (with the exception of the town of Broken Hill), Victoria, Tasmania and the Australian Capital Territory. AEST is equal to Coordinated Universal Time plus 10 hours (UTC +10). Australian Central Standard Time (ACST) Covers the state of South Australia, the town of Broken Hill in western New South Wales and the Northern Territory. ACST is equal to Coordinated Universal Time plus 9 ½ hours (UTC +9 ½). Australian Western Standard Time (AWST) Covers Western Australia. AWST is equal to Coordinated Universal Time plus 8 hours (UTC +8). Daylight saving Daylight Saving Time (DST) is the practice of advancing clocks one hour during the warmer months of the year. In Australia, Daylight saving is observed in New South Wales, Victoria, South Australia, Tasmania, and the Australian Capital Territory. Daylight Saving Time begins at 2am (AEST) on the first Sunday in October and ends at 2am (AEST) (which is 3am Australian Eastern Daylight Time) on the first Sunday in April. Where Daylight saving is observed: NSW, ACT,Vic and Tas move from AEST to Australian Eastern Daylight Time (AEDT), and clocks are advanced to UTC +11. SA and the NSW town of Broken Hill move from ACST to Australian Central Daylight Time (ACDT), and clocks are advanced to UTC +10 ½. Daylight saving is not observed in Queensland, the Northern Territory or Western Australia. ================================================================================ I believe that the abbreviations used on the federal government website should be used. Shaun Bouckaert

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leap seconds (srsly)
by Zefram Nov. 4, 2011

Nov. 4, 2011

In a couple of months, a decision is going to be made about possibly ceasing leap seconds in UTC. If that happens, the tz database is going to be thrown into a world of hurt, as "UTC = GMT" gradually ceases to be a viable approximation. Here are the slides from a talk presented a couple of months ago that provides a useful primer on how the decision would interact with civil and legal time: http://www.cacr.caltech.edu/futureofutc/program/presentations/AAS_11-662_Se… All the presentations from the conference where that was presented, discussing mary aspects of the decision, can be found here: http://www.cacr.caltech.edu/futureofutc/program/ (Information forwarded from the leapsecs mailing list.) -zefram

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Leap seconds
by Thom Hehl Nov. 4, 2011

Nov. 4, 2011

The docs specify that the transition time is based on the return value from the time() function. Does that mean that the leap seconds are automatically adjusted based on that value and the transition time is correct or does that mean that it uses the actual time and I have to adjust first with leap seconds if I want an accurate conversion?

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Thread-safe localtime(3) (was Re: Reading binary files)
by Bennett Todd Nov. 3, 2011

Nov. 3, 2011

Am I missing a fundamental, or would it be reasonable to not necessarily expose the data structure for the parsed conversion data, but instead offer explicit parse routine (returning an opaque blob) and convert routine that takes such a blob as a parameter? Then it should be easy to make tzset(3) utterly trivial -- call the zoninfo parser on getenv(TZ) with locking, and localtime(3) likewise trivial, call the real convert routine with the datastructure cached by the latest tzset.

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Re: [tz] Reading binary files
by Thom Hehl Nov. 2, 2011

Nov. 2, 2011

Not if you are writing applications that need high performance processing of multiple timezones and access from multiple languages and platforms. Besides, we're multi-threaded. Changing environment variables is simply not an option. Yikes! Can you say race condition. From: bent(a)latency.net [mailto:bent@latency.net] On Behalf Of Bennett Todd Sent: Wednesday, November 02, 2011 9:09 AM To: Thom Hehl Subject: Re: [tz] Reading binary files The binary files are a distraction. What you want to do is set the environment variable TZ to the name of the zone you want, then call tzset which is what consults the database and prepares for conversion. Then localtime(3) will translate a time_t (seconds since the epoch) to hours, minutes, seconds, etc in the local timezone. For translating back and forth you repeatedly reset TZ, call tzset(3), and localtime(3). Those are the standards for Unix, the native home of the zoneinfo database. If you're on a different system details may vary. But on Unix the database is probably already installed in your system and the subroutines you need are already compiled into the system library.

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