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Newsgroups: comp.unix.misc,comp.std.internat,comp.lang.c,comp.unix.admin
Path: sparky!uunet!cs.utexas.edu!usc!snorkelwacker.mit.edu!
thunder.mcrcim.mcgill.edu!sobeco!seanm
From: se...@sobeco.com (s.macguire)
Subject: Daylight Savings time in the UK
Organization: Sobeco Ernst & Young
Date: Sun, 21 Jun 92 22:01:04 GMT
Message-ID: <1992Jun21.220104.10582@sobeco.com>
Keywords: daylight time localtime
Lines: 16

The problem is simple.  It takes an act of parliament to change the time
from GMT to BST (British Summer time).  Needless to say localtime() is
firmly stuck in the North American way.  Thus, many computers in the UK are
fudged by hand for the week or so that the US and UK are out of sync.

Have there been any changes to localtime(), or the TZ environment variable
to cope with this mess; I've seen some horrible things done to the TZ
variable in Brussels (lots of semicolons and numbers afterwards), but
wondered if there was any proper standard.

Thanks in advance.
___
Sean MacGuire						uunet!sobeco!sean
The MacLawran Group Inc, Montreal 			(514) 982-9688
			"No insurance, no surrender"

Path: sparky!uunet!auspex-gw!guy
From: g...@Auspex.COM (Guy Harris)
Newsgroups: comp.unix.misc,comp.std.internat,comp.lang.c,comp.unix.admin
Subject: Re: Daylight Savings time in the UK
Keywords: daylight time localtime
Message-ID: <13205@auspex-gw.auspex.com>
Date: 21 Jun 92 23:28:18 GMT
References: <1992Jun21.220104.10582@sobeco.com>
Sender: n...@auspex-gw.auspex.com
Followup-To: comp.unix.misc
Organization: Auspex Systems, Santa Clara
Lines: 43
Nntp-Posting-Host: auspex.auspex.com

[Followups redirected to "comp.unix.misc"; it's not a C-language issue,
as different C language implementations handle time zones differently,
if they handle it at all.  "C: it's not just for UNIX any more!"]

>The problem is simple.  It takes an act of parliament to change the time
>from GMT to BST (British Summer time).  Needless to say localtime() is
>firmly stuck in the North American way.

True on some systems.  False on others.  The UNIX system on which I'm
typing this has the Arthur Olson time zone code, so it supports plenty
of different time zones, and new ones can be added or old ones can be
changed easily.

>Have there been any changes to localtime(), or the TZ environment variable
>to cope with this mess; I've seen some horrible things done to the TZ
>variable in Brussels (lots of semicolons and numbers afterwards), but
>wondered if there was any proper standard.

Unfortunately, the horrible syntax you saw is probably the one specified
by POSIX 1003.1 as a standard; while it's a "proper standard" in the
sense of being part of an Official Standard (POSIX 1003.1, which may
even be an ISO standard at this point), it's not a particularly proper
scheme for dealing with multiple time zones, given the horrible syntax.

Fortunately, POSIX 1003.1 leaves room to implement both the crufty POSIX
scheme and the nice Arthur Olson scheme in the same system; in the POSIX
scheme, you'd have to construct some string of the sort you saw, but in
the Arthur Olson scheme, setting TZ to "GB-Eire" is sufficient, and to
change the rules to match what the Act of Parliament in question
specifies, you edit a text file and "recompile" it with the "zic"
command.

Many UNIX systems these days have either a scheme like the POSIX one
(SVR3.1 and later have a scheme of that sort, although it only lets you
specify the start and end date for the current year; systems with the
full POSIX scheme let you specify a rule for the start and end date *as
long as it's sufficiently regular* - unfortunately, in many countries it
*isn't* sufficiently regular) or the Arthur Olson one or both.  (SunOS
4.x has the Olson scheme, and both in SunOS 4.1[.x]; SVR4 has both,
although not all SVR4 implementations necessarily come with the files
the Olson code requires - they may be supplied in the source you buy
from USL, but binary distributions might not have them; other systems
also have one or the other or both.)

Path: sparky!uunet!mcsun!sun4nl!tuegate.tue.nl!rwc.urc.tue.nl!tgcpwd
From: tgc...@rwc.urc.tue.nl (Wim van Dorst)
Newsgroups: comp.unix.misc
Subject: Re: Daylight Savings time in the UK
Keywords: daylight time localtime
Message-ID: <4480@tuegate.tue.nl>
Date: 22 Jun 92 06:59:29 GMT
References: <1992Jun21.220104.10582@sobeco.com> <13205@auspex-gw.auspex.com>
Sender: r...@tuegate.tue.nl
Reply-To: tgc...@urc.tue.nl
Organization: Eindhoven University of Technology, The Netherlands
Lines: 20

In article <13...@auspex-gw.auspex.com> g...@Auspex.COM (Guy Harris) writes:
>Fortunately, POSIX 1003.1 leaves room to implement both the crufty POSIX
>scheme and the nice Arthur Olson scheme in the same system; in the POSIX
>scheme, you'd have to construct some string of the sort you saw, but in
>the Arthur Olson scheme, setting TZ to "GB-Eire" is sufficient, 

What is the Olson scheme/code? I know about the Posix standard as I
implemented it on my system my self, but I haven't heard of the Olson
TZ standard. Is it publicized somewhere? Is the source available? Is
documentation available (The P1003.1 book is very clear on TZ IMHO)?

When you could please elaborate a bit on the Olson Scheme, I (and perhaps
others) would be most obliged.

Met vriendelijke groeten, Wim `Blue Baron' van Dorst
-- 
---------------------------------------------------------------------
Blue Baron = Wim van Dorst, Voice (+31) 074-443937, (+31) 02152-42319
(-:       ba...@wiesje.hobby.nl           tgc...@urc.tue.nl       :-)
---------------------------------------------------------------------

Newsgroups: comp.unix.misc
Path: sparky!uunet!zaphod.mps.ohio-state.edu!sol.ctr.columbia.edu!usc!
ucla-cs!twinsun!eggert
From: egg...@bi.twinsun.com (Paul Eggert)
Subject: Re: Daylight Savings time in the UK
Message-ID: <bi7Mq3GV@twinsun.com>
Keywords: daylight time localtime
Sender: use...@twinsun.com
Nntp-Posting-Host: bi
Organization: Twin Sun, Inc
References: <1992Jun21.220104.10582@sobeco.com> <13205@auspex-gw.auspex.com> 
<4480@tuegate.tue.nl>
Date: Mon, 22 Jun 1992 20:06:34 GMT
Lines: 97

tgc...@rwc.urc.tue.nl (Wim van Dorst) asks ``What is the Olson scheme/code?''

The Olson method is referred to in the Posix standard (see Posix
1003.1-1990 section B.8.1.1).  It's an excellent package, and is
becoming the standard in modern Unix systems.  It uses the TZ
environment variable as an index into a table on disk that contains
rules that are sensitive to the year to which they are applied.  The
table is compiled from a human-readable text file.  The package can
handle a wide variety of time zone anomalies, including
double-daylight, leap seconds, different rules for different years, and
so forth.  If your government changes your timekeeping rules, all you
need to do is write up the new rules, run the `zic' program on them,
and your programs can use the new rules without recompilation or relinking.

You can FTP the Olson code from elsie.nci.nih.gov in pub/tz92.tar.Z.

To give you a feeling of what the Olson format rules look like,
(and how much politics influences timekeeping!),
here are the rules for TZ=GB-Eire as published in tz92.


# [British Summer Time] is fixed annually by Act of Parliament.
# If you can predict what Parliament will do, you should be in
# politics making a fortune, not computing.

# Zone	NAME		GMTOFF	RULES/SAVE	FORMAT	[UNTIL]
Zone	GB-Eire		0:00	GB-Eire		%s	1968 Oct 27 1:00s
			1:00	-		BST	1971 Oct 31 1:00s
			0:00	GB-Eire		%s

# Rule	NAME	FROM	TO	TYPE	IN	ON	AT	SAVE	LETTER/S
# 1916 to 1925--irregular
Rule	GB-Eire	1916	only	-	Mar	21	1:00s	1:00	BST
Rule	GB-Eire	1916	only	-	Oct	1	1:00s	0	GMT
Rule	GB-Eire	1917	only	-	Apr	8	1:00s	1:00	BST
Rule	GB-Eire	1917	only	-	Sep	17	1:00s	0	GMT
Rule	GB-Eire	1918	only	-	Mar	24	1:00s	1:00	BST
Rule	GB-Eire	1918	only	-	Sep	30	1:00s	0	GMT
Rule	GB-Eire	1919	only	-	Mar	30	1:00s	1:00	BST
Rule	GB-Eire	1919	only	-	Sep	29	1:00s	0	GMT
Rule	GB-Eire	1920	only	-	Mar	28	1:00s	1:00	BST
Rule	GB-Eire	1920	only	-	Oct	25	1:00s	0	GMT
Rule	GB-Eire	1921	only	-	Apr	3	1:00s	1:00	BST
Rule	GB-Eire	1921	only	-	Oct	3	1:00s	0	GMT
Rule	GB-Eire	1922	only	-	Mar	26	1:00s	1:00	BST
Rule	GB-Eire	1922	only	-	Oct	8	1:00s	0	GMT
Rule	GB-Eire	1923	only	-	Apr	22	1:00s	1:00	BST
Rule	GB-Eire	1923	only	-	Oct	16	1:00s	0	GMT
Rule	GB-Eire	1924	only	-	Apr	30	1:00s	1:00	BST
Rule	GB-Eire	1924	only	-	Sep	21	1:00s	0	GMT
# 1925 to 1939 start--regular
Rule	GB-Eire	1925	1939	-	Apr	Sun>=15	1:00s	1:00	BST
Rule	GB-Eire	1925	1938	-	Oct	Sun>=1	1:00s	0	GMT
# 1939 end to 1947--irregular, and with double summer time
Rule	GB-Eire	1939	only	-	Nov	19	1:00s	0	GMT
Rule	GB-Eire	1940	only	-	Feb	25	1:00s	1:00	BST
Rule	GB-Eire	1941	only	-	May	4	1:00s	2:00	DST
Rule	GB-Eire	1941	only	-	Aug	10	1:00s	1:00	BST
Rule	GB-Eire	1942	only	-	Apr	5	1:00s	2:00	DST
Rule	GB-Eire	1942	only	-	Aug	9	1:00s	1:00	BST
Rule	GB-Eire	1943	only	-	Apr	4	1:00s	2:00	DST
Rule	GB-Eire	1943	only	-	Aug	15	1:00s	1:00	BST
Rule	GB-Eire	1944	only	-	Apr	2	1:00s	2:00	DST
Rule	GB-Eire	1944	only	-	Sep	17	1:00s	1:00	BST
# Double daylight starts on a Monday in 1945?
Rule	GB-Eire	1945	only	-	Apr	2	1:00s	2:00	DST
Rule	GB-Eire	1945	only	-	Jul	15	1:00s	1:00	BST
Rule	GB-Eire	1945	only	-	Oct	7	1:00s	0	GMT
Rule	GB-Eire	1946	only	-	Apr	14	1:00s	1:00	BST
Rule	GB-Eire	1946	only	-	Oct	6	1:00s	0	GMT
Rule	GB-Eire	1947	only	-	Mar	16	1:00s	1:00	BST
Rule	GB-Eire	1947	only	-	Apr	13	1:00s	2:00	DST
Rule	GB-Eire	1947	only	-	Aug	10	1:00s	1:00	BST
Rule	GB-Eire	1947	only	-	Nov	2	1:00s	0	GMT
# So much for double saving time.  1948 and 1949, irregular.
Rule	GB-Eire	1948	only	-	Mar	14	1:00s	1:00	BST
Rule	GB-Eire	1948	only	-	Oct	31	1:00s	0	GMT
Rule	GB-Eire	1949	only	-	Apr	3	1:00s	1:00	BST
Rule	GB-Eire	1949	only	-	Oct	30	1:00s	0	GMT
# 1950 through start of 1953, regular.
Rule	GB-Eire	1950	1953	-	Apr	Sun>=14	1:00s	1:00	BST
Rule	GB-Eire	1950	1952	-	Oct	Sun>=21	1:00s	0	GMT
# 1954 to 1980, starting rules
Rule	GB-Eire	1954	only	-	Apr	11	1:00s	1:00	BST
Rule	GB-Eire	1955	1959	-	Apr	Sun>=14	1:00s	1:00	BST
Rule	GB-Eire	1960	only	-	Apr	10	1:00s	1:00	BST
Rule	GB-Eire	1961	1963	-	Mar	lastSun	1:00s	1:00	BST
Rule	GB-Eire	1964	1967	-	Mar	Sun>=19	1:00s	1:00	BST
Rule	GB-Eire	1968	only	-	Feb	18	1:00s	1:00	BST
Rule	GB-Eire	1972	1980	-	Mar	Sun>=16	1:00s	1:00	BST
# 1953 to 1971, ending rules
Rule	GB-Eire	1953	1960	-	Oct	Sun>=1	1:00s	0	GMT
Rule	GB-Eire	1961	1967	-	Oct	Sun>=23	1:00s	0	GMT
Rule	GB-Eire	1971	only	-	Oct	31	1:00s	0	GMT
# Current rules
Rule	GB-Eire	1981	max	-	Mar	lastSun	1:00s	1:00	BST
Rule	GB-Eire	1972	max	-	Oct	Sun>=23	1:00s	0	GMT