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NEWS
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News for the tz database
Release 2021c - 2021-10-01 14:21:49 -0700
Briefly:
Revert most 2021b changes to 'backward'.
Fix 'zic -b fat' bug in pre-1970 32-bit data.
Fix two Link line typos.
Distribute SECURITY file.
This release is intended as a bugfix release, to fix compatibility
problems and typos reported since 2021b was released.
Changes to Link directives
Revert almost all of 2021b's changes to the 'backward' file,
by moving Link directives back to where they were in 2021a.
Although 'zic' doesn't care which source file contains a Link
directive, some downstream uses ran into trouble with the move.
(Problem reported by Stephen Colebourne for Joda-Time.)
Fix typo that linked Atlantic/Jan_Mayen to the wrong location
(problem reported by Chris Walton).
Fix 'backzone' typo that linked America/Virgin to the wrong
location (problem reported by Michael Deckers).
Changes to code
Fix a bug in 'zic -b fat' that caused old timestamps to be
mishandled in 32-bit-only readers (problem reported by Daniel
Fischer).
Changes to documentation
Distribute the SECURITY file (problem reported by Andreas Radke).
Release 2021b - 2021-09-24 16:23:00 -0700
Briefly:
Jordan now starts DST on February's last Thursday.
Samoa no longer observes DST.
Merge more location-based Zones whose timestamps agree since 1970.
Move some backward-compatibility links to 'backward'.
Rename Pacific/Enderbury to Pacific/Kanton.
Correct many pre-1993 transitions in Malawi, Portugal, etc.
zic now creates each output file or link atomically.
zic -L no longer omits the POSIX TZ string in its output.
zic fixes for truncation and leap second table expiration.
zic now follows POSIX for TZ strings using all-year DST.
Fix some localtime crashes and bugs in obscure cases.
zdump -v now outputs more-useful boundary cases.
tzfile.5 better matches a draft successor to RFC 8536.
A new file SECURITY.
This release is prompted by recent announcements by Jordan and Samoa.
It incorporates many other changes that had accumulated since 2021a.
However, it omits most proposed changes that merged all Zones
agreeing since 1970, as concerns were raised about doing too many of
these changes at once. It does keeps some of these changes in the
interest of making tzdb more equitable one step at a time; see
"Merge more location-based Zones" below.
Changes to future timestamps
Jordan now starts DST on February's last Thursday.
(Thanks to Steffen Thorsen.)
Samoa no longer observes DST. (Thanks to Geoffrey D. Bennett.)
Changes to zone name
Rename Pacific/Enderbury to Pacific/Kanton. When we added
Enderbury in 1993, we did not know that it is uninhabited and that
Kanton (population two dozen) is the only inhabited location in
that timezone. The old name is now a backward-compatility link.
Changes to past timestamps
Correct many pre-1993 transitions, fixing entries originally
derived from Shanks, Whitman, and Mundell. The fixes include:
- Barbados: standard time was introduced in 1911, not 1932; and
DST was observed in 1942-1944
- Cook Islands: In 1899 they switched from east to west of GMT,
celebrating Christmas for two days. They (and Niue) switched
to standard time in 1952, not 1901.
- Guyana: corrected LMT for Georgetown; the introduction of
standard time in 1911, not 1915; and corrections to 1975 and
1992 transitions
- Kanton: uninhabited before 1937-08-31
- Niue: only observed -11:20 from 1952 through 1964, then went to
-11 instead of -11:30
- Portugal: DST was observed in 1950
- Tonga: corrected LMT; the introduction of standard time in 1945,
not 1901; and corrections to the transition from +12:20 to +13
in 1961, not 1941
Additional fixes to entries in the 'backzone' file include:
- Enderbury: inhabited only 1860/1885 and 1938-03-06/1942-02-09
- The Gambia: 1933 and 1942 transitions
- Malawi: several 1911 through 1925 transitions
- Sierra Leone: several 1913 through 1941 transitions, and DST
was NOT observed in 1957 through 1962
(Thanks to P Chan, Michael Deckers, Alexander Krivenyshev and
Alois Treindl.)
Merge more location-based Zones whose timestamps agree since 1970,
as pre-1970 timestamps are out of scope. This is part of a
process that has been ongoing since 2013. This does not affect
post-1970 timestamps, and timezone historians who build with 'make
PACKRATDATA=backzone' should see no changes to pre-1970 timestamps.
When merging, keep the most-populous location's data, and move
data for other locations to 'backzone' with a backward
link in 'backward'. For example, move America/Creston data to
'backzone' with a link in 'backward' from America/Phoenix because
the two timezones' timestamps agree since 1970; this change
affects some pre-1968 timestamps in America/Creston because
Creston and Phoenix disagreed before 1968. The affected Zones
are Africa/Accra, America/Atikokan, America/Blanc-Sablon,
America/Creston, America/Curacao, America/Nassau,
America/Port_of_Spain, Antarctica/DumontDUrville, and
Antarctica/Syowa.
Changes to maintenance procedure
The new file SECURITY covers how to report security-related bugs.
Several backward-compatibility links have been moved to the
'backward' file. These links, which range from Africa/Addis_Ababa
to Pacific/Saipan, are only for compatibility with now-obsolete
guidelines suggesting an entry for every ISO 3166 code.
The intercontinental convenience links Asia/Istanbul and
Europe/Nicosia have also been moved to 'backward'.
Changes to code
zic now creates each output file or link atomically,
possibly by creating a temporary file and then renaming it.
This avoids races where a TZ setting would temporarily stop
working while zic was installing a replacement file or link.
zic -L no longer omits the POSIX TZ string in its output.
Starting with 2020a, zic -L truncated its output according to the
"Expires" directive or "#expires" comment in the leapseconds file.
The resulting TZif files omitted daylight saving transitions after
the leap second table expired, which led to far less-accurate
predictions of times after the expiry. Although future timestamps
cannot be converted accurately in the presence of leap seconds, it
is more accurate to convert near-future timestamps with a few
seconds error than with an hour error, so zic -L no longer
truncates output in this way.
Instead, when zic -L is given the "Expires" directive, it now
outputs the expiration by appending a no-change entry to the leap
second table. Although this should work well with most TZif
readers, it does not conform to Internet RFC 8536 and some pickier
clients (including tzdb 2017c through 2021a) reject it, so
"Expires" directives are currently disabled by default. To enable
them, set the EXPIRES_LINE Makefile variable. If a TZif file uses
this new feature it is marked with a new TZif version number 4,
a format intended to be documented in a successor to RFC 8536.
zic -L LEAPFILE -r @LO no longer generates an invalid TZif file
that omits leap second information for the range LO..B when LO
falls between two leap seconds A and B. Instead, it generates a
TZif version 4 file that represents the previously-missing
information.
The TZif reader now allows the leap second table to begin with a
correction other than -1 or +1, and to contain adjacent
transitions with equal corrections. This supports TZif version 4.
The TZif reader now lets leap seconds occur less than 28 days
apart. This supports possible future TZif extensions.
Fix bug that caused 'localtime' etc. to crash when TZ was
set to a all-year DST string like "EST5EDT4,0/0,J365/25" that does
not conform to POSIX but does conform to Internet RFC 8536.
Fix another bug that caused 'localtime' etc. to crash when TZ was
set to a POSIX-conforming but unusual TZ string like
"EST5EDT4,0/0,J365/0", where almost all the year is DST.
Fix yet another bug that caused 'localtime' etc. to mishandle slim
TZif files containing leap seconds after the last explicit
transition in the table, or when handling far-future timestamps
in slim TZif files lacking leap seconds.
Fix localtime misbehavior involving positive leap seconds.
This change affects only behavior for "right" system time,
which contains leap seconds, and only if the UT offset is
not a multiple of 60 seconds when a positive leap second occurs.
(No such timezone exists in tzdb, luckily.) Without the fix,
the timestamp was ambiguous during a positive leap second.
With the fix, any seconds occurring after a positive leap second
and within the same localtime minute are counted through 60, not
through 59; their UT offset (tm_gmtoff) is the same as before.
Here is how the fix affects timestamps in a timezone with UT
offset +01:23:45 (5025 seconds) and with a positive leap second at
1972-06-30 23:59:60 UTC (78796800):
time_t without the fix with the fix
78796800 1972-07-01 01:23:45 1972-07-01 01:23:45 (leap second)
78796801 1972-07-01 01:23:45 1972-07-01 01:23:46
...
78796815 1972-07-01 01:23:59 1972-07-01 01:23:60
78796816 1972-07-01 01:24:00 1972-07-01 01:24:00
Fix an unlikely bug that caused 'localtime' etc. to misbehave if
civil time changes a few seconds before time_t wraps around, when
leap seconds are enabled.
Fix bug in zic -r; in some cases, the dummy time type after the
last time transition disagreed with the TZ string, contrary to
Internet RFC 8563 section 3.3.
Fix a bug with 'zic -r @X' when X is a negative leap second that
has a nonnegative correction. Without the fix, the output file
was truncated so that X appeared to be a positive leap second.
Fix a similar, even-less-likely bug when truncating at a positive
leap second that has a nonpositive correction.
zic -r now reports an error if given rolling leap seconds, as this
usage has never generally worked and is evidently unused.
zic now generates a POSIX-conforming TZ string for TZif files
where all-year DST is predicted for the indefinite future.
For example, for all-year Eastern Daylight Time, zic now generates
"XXX3EDT4,0/0,J365/23" where it previously generated
"EST5EDT,0/0,J365/25" or "". (Thanks to Michael Deckers for
noting the possibility of POSIX conformance.)
zic.c no longer requires sys/wait.h (thanks to spazmodius for
noting it wasn't needed).
When reading slim TZif files, zdump no longer mishandles leap
seconds on the rare platforms where time_t counts leap seconds,
fixing a bug introduced in 2014g.
zdump -v now outputs timestamps at boundaries of what localtime
and gmtime can represent, instead of the less-useful timestamps
one day after the minimum and one day before the maximum.
(Thanks to Arthur David Olson for prototype code, and to Manuela
Friedrich for debugging help.)
zdump's -c and -t options are now consistently inclusive for the
lower time bound and exclusive for the upper. Formerly they were
inconsistent. (Confusion noted by Martin Burnicki.)
Changes to build procedure
You can now compile with -DHAVE_MALLOC_ERRNO=0 to port to
non-POSIX hosts where malloc doesn't set errno.
(Problem reported by Jan Engelhardt.)
Changes to documentation
tzfile.5 better matches a draft successor to RFC 8536
<https://datatracker.ietf.org/doc/draft-murchison-rfc8536bis/01/>.
Release 2021a - 2021-01-24 10:54:57 -0800
Changes to future timestamps
South Sudan changes from +03 to +02 on 2021-02-01 at 00:00.
(Thanks to Steffen Thorsen.)
Release 2020f - 2020-12-29 00:17:46 -0800
Change to build procedure
'make rearguard_tarballs' no longer generates a bad rearguard.zi,
fixing a 2020e bug. (Problem reported by Deborah Goldsmith.)
Release 2020e - 2020-12-22 15:14:34 -0800
Briefly:
Volgograd switches to Moscow time on 2020-12-27 at 02:00.
Changes to future timestamps
Volgograd changes time zone from +04 to +03 on 2020-12-27 at 02:00.
(Thanks to Alexander Krivenyshev and Stepan Golosunov.)
Changes to past timestamps
Correct many pre-1986 transitions, fixing entries originally
derived from Shanks. The fixes include:
- Australia: several 1917 through 1971 transitions
- The Bahamas: several 1941 through 1945 transitions
- Bermuda: several 1917 through 1956 transitions
- Belize: several 1942 through 1968 transitions
- Ghana: several 1915 through 1956 transitions
- Israel and Palestine: several 1940 through 1985 transitions
- Kenya and adjacent: several 1908 through 1960 transitions
- Nigeria and adjacent: correcting LMT in Lagos, and several 1905
through 1919 transitions
- Seychelles: the introduction of standard time in 1907, not 1906
- Vanuatu: DST in 1973-1974, and a corrected 1984 transition
(Thanks to P Chan.)
Because of the Australia change, Australia/Currie (King Island) is
no longer needed, as it is identical to Australia/Hobart for all
timestamps since 1970 and was therefore created by mistake.
Australia/Currie has been moved to the 'backward' file and its
corrected data moved to the 'backzone' file.
Changes to past time zone abbreviations and DST flags
To better match legislation in Turks and Caicos, the 2015 shift to
year-round observance of -04 is now modeled as AST throughout before
returning to Eastern Time with US DST in 2018, rather than as
maintaining EDT until 2015-11-01. (Thanks to P Chan.)
Changes to documentation
The zic man page now documents zic's coalescing of transitions
when a zone falls back just before DST springs forward.
Release 2020d - 2020-10-21 11:24:13 -0700
Briefly:
Palestine ends DST earlier than predicted, on 2020-10-24.
Changes to past and future timestamps
Palestine ends DST on 2020-10-24 at 01:00, instead of 2020-10-31
as previously predicted (thanks to Sharef Mustafa.) Its
2019-10-26 fall-back was at 00:00, not 01:00 (thanks to Steffen
Thorsen.) Its 2015-10-23 transition was at 01:00 not 00:00, and
its spring 2020 transition was on March 28 at 00:00, not March 27
(thanks to Pierre Cashon.) This affects Asia/Gaza and
Asia/Hebron. Assume future spring and fall transitions will be on
the Saturday preceding the last Sunday of March and October,
respectively.
Release 2020c - 2020-10-16 11:15:53 -0700
Briefly:
Fiji starts DST later than usual, on 2020-12-20.
Changes to future timestamps
Fiji will start DST on 2020-12-20, instead of 2020-11-08 as
previously predicted. DST will still end on 2021-01-17.
(Thanks to Raymond Kumar and Alan Mintz.) Assume for now that
the later-than-usual start date is a one-time departure from the
recent pattern.
Changes to build procedure
Rearguard tarballs now contain an empty file pacificnew.
Some older downstream software expects this file to exist.
(Problem reported by Mike Cullinan.)
Release 2020b - 2020-10-06 18:35:04 -0700
Briefly:
Revised predictions for Morocco's changes starting in 2023.
Canada's Yukon changes to -07 on 2020-11-01, not 2020-03-08.
Macquarie Island has stayed in sync with Tasmania since 2011.
Casey, Antarctica is at +08 in winter and +11 in summer.
zic no longer supports -y, nor the TYPE field of Rules.
Changes to future timestamps
Morocco's spring-forward after Ramadan is now predicted to occur
no sooner than two days after Ramadan, instead of one day.
(Thanks to Milamber.) The first altered prediction is for 2023,
now predicted to spring-forward on April 30 instead of April 23.
Changes to past and future timestamps
Casey Station, Antarctica has been using +08 in winter and +11 in
summer since 2018. The most recent transition from +08 to +11 was
2020-10-04 00:01. Also, Macquarie Island has been staying in
sync with Tasmania since 2011. (Thanks to Steffen Thorsen.)
Changes to past and future time zone abbreviations and DST flags
Canada's Yukon, represented by America/Whitehorse and
America/Dawson, changes its time zone rules from -08/-07 to
permanent -07 on 2020-11-01, not on 2020-03-08 as 2020a had it.
This change affects only the time zone abbreviation (MST vs PDT)
and daylight saving flag for the period between the two dates.
(Thanks to Andrew G. Smith.)
Changes to past timestamps
Correct several transitions for Hungary for 1918/1983.
For example, the 1983-09-25 fall-back was at 01:00, not 03:00.
(Thanks to Géza Nyáry.) Also, the 1890 transition to standard
time was on 11-01, not 10-01 (thanks to Michael Deckers).
The 1891 French transition was on March 16, not March 15. The
1911-03-11 French transition was at midnight, not a minute later.
Monaco's transitions were on 1892-06-01 and 1911-03-29, not
1891-03-15 and 1911-03-11. (Thanks to Michael Deckers.)
Changes to code
Support for zic's long-obsolete '-y YEARISTYPE' option has been
removed and, with it, so has support for the TYPE field in Rule
lines, which is now reserved for compatibility with earlier zic.
These features were previously deprecated in release 2015f.
(Thanks to Tim Parenti.)
zic now defaults to '-b slim' instead of to '-b fat'.
zic's new '-l -' and '-p -' options uninstall any existing
localtime and posixrules files, respectively.
The undocumented and ineffective tzsetwall function has been
removed.
Changes to build procedure
The Makefile now defaults POSIXRULES to '-', so the posixrules
feature (obsolete as of 2019b) is no longer installed by default.
Changes to documentation and commentary
The long-obsolete files pacificnew, systemv, and yearistype.sh have
been removed from the distribution. (Thanks to Tim Parenti.)
Release 2020a - 2020-04-23 16:03:47 -0700
Briefly:
Morocco springs forward on 2020-05-31, not 2020-05-24.
Canada's Yukon advanced to -07 year-round on 2020-03-08.
America/Nuuk renamed from America/Godthab.
zic now supports expiration dates for leap second lists.
Changes to future timestamps
Morocco's second spring-forward transition in 2020 will be May 31,
not May 24 as predicted earlier. (Thanks to Semlali Naoufal.)
Adjust future-year predictions to use the first Sunday after the
day after Ramadan, not the first Sunday after Ramadan.
Canada's Yukon, represented by America/Whitehorse and
America/Dawson, advanced to -07 year-round, beginning with its
spring-forward transition on 2020-03-08, and will not fall back on
2020-11-01. Although a government press release calls this
"permanent Pacific Daylight Saving Time", we prefer MST for
consistency with nearby Dawson Creek, Creston, and Fort Nelson.
(Thanks to Tim Parenti.)
Changes to past timestamps
Shanghai observed DST in 1919. (Thanks to Phake Nick.)
Changes to timezone identifiers
To reflect current usage in English better, America/Godthab has
been renamed to America/Nuuk. A backwards-compatibility link
remains for the old name.
Changes to code
localtime.c no longer mishandles timestamps after the last
transition in a TZif file with leap seconds and with daylight
saving time transitions projected into the indefinite future.
For example, with TZ='America/Los_Angeles' with leap seconds,
zdump formerly reported a DST transition on 2038-03-14
from 01:59:32.999... to 02:59:33 instead of the correct transition
from 01:59:59.999... to 03:00:00.
zic -L now supports an Expires line in the leapseconds file, and
truncates the TZif output accordingly. This propagates leap
second expiration information into the TZif file, and avoids the
abovementioned localtime.c bug as well as similar bugs present in
many client implementations. If no Expires line is present, zic
-L instead truncates the TZif output based on the #expires comment
present in leapseconds files distributed by tzdb 2018f and later;
however, this usage is obsolescent. For now, the distributed
leapseconds file has an Expires line that is commented out, so
that the file can be fed to older versions of zic which ignore the
commented-out line. Future tzdb distributions are planned to
contain a leapseconds file with an Expires line.
The configuration macros HAVE_TZNAME and USG_COMPAT should now be
set to 1 if the system library supports the feature, and 2 if not.
As before, these macros are nonzero if tzcode should support the
feature, zero otherwise.
The configuration macro ALTZONE now has the same values with the
same meaning as HAVE_TZNAME and USG_COMPAT.
The code's defense against CRLF in leap-seconds.list is now
portable to POSIX awk. (Problem reported by Deborah Goldsmith.)
Although the undocumented tzsetwall function is not changed in
this release, it is now deprecated in preparation for removal in
future releases. Due to POSIX requirements, tzsetwall has not
worked for some time. Any code that uses it should instead use
tzalloc(NULL) or, if portability trumps thread-safety, should
unset the TZ environment variable.
Changes to commentary
The Îles-de-la-Madeleine and the Listuguj reserve are noted as
following America/Halifax, and comments about Yukon's "south" and
"north" have been corrected to say "east" and "west". (Thanks to
Jeffery Nichols.)
Release 2019c - 2019-09-11 08:59:48 -0700
Briefly:
Fiji observes DST from 2019-11-10 to 2020-01-12.
Norfolk Island starts observing Australian-style DST.
Changes to future timestamps
Fiji's next DST transitions will be 2019-11-10 and 2020-01-12
instead of 2019-11-03 and 2020-01-19. (Thanks to Raymond Kumar.)
Adjust future guesses accordingly.
Norfolk Island will observe Australian-style DST starting in
spring 2019. The first transition is on 2019-10-06. (Thanks to
Kyle Czech and Michael Deckers.)
Changes to past timestamps
Many corrections to time in Turkey from 1940 through 1985.
(Thanks to Oya Vulaş via Alois Treindl, and to Kıvanç Yazan.)
The Norfolk Island 1975-03-02 transition was at 02:00 standard
time, not 02:00 DST. (Thanks to Michael Deckers.)
South Korea observed DST from 1948 through 1951. Although this
info was supposed to appear in release 2014j, a typo inadvertently
suppressed the change. (Thanks to Alois Treindl.)
Detroit observed DST in 1967 and 1968 following the US DST rules,
except that its 1967 DST began on June 14 at 00:01. (Thanks to
Alois Treindl for pointing out that the old data entries were
probably wrong.)
Fix several errors in pre-1970 transitions in Perry County, IN.
(Thanks to Alois Triendl for pointing out the 1967/9 errors.)
Edmonton did not observe DST in 1967 or 1969. In 1946 Vancouver
ended DST on 09-29 not 10-13, and Vienna ended DST on 10-07 not
10-06. In 1945 Königsberg (now Kaliningrad) switched from +01/+02
to +02/+03 on 04-10 not 01-01, and its +02/+03 is abbreviated
EET/EEST, not CET/CEST. (Thanks to Alois Triendl.) In 1946
Königsberg switched to +03 on 04-07 not 01-01.
In 1946 Louisville switched from CST to CDT on 04-28 at 00:01, not
01-01 at 00:00. (Thanks to Alois Treindl and Michael Deckers.)
Also, it switched from CST to CDT on 1950-04-30, not 1947-04-27.
The 1892-05-01 transition in Brussels was at 00:17:30, not at noon.
(Thanks to Michael Deckers.)
Changes to past time zone abbreviations and DST flags
Hong Kong Winter Time, observed from 1941-10-01 to 1941-12-25,
is now flagged as DST and is abbreviated HKWT not HKT.
Changes to code
leapseconds.awk now relies only on its input data, rather than
also relying on its comments. (Inspired by code from Dennis
Ferguson and Chris Woodbury.)
The code now defends against CRLFs in leap-seconds.list.
(Thanks to Brian Inglis and Chris Woodbury.)
Changes to documentation and commentary
theory.html discusses leap seconds. (Thanks to Steve Summit.)
Nashville's newspapers dueled about the time of day in the 1950s.
(Thanks to John Seigenthaler.)
Liechtenstein observed Swiss DST in 1941/2.
(Thanks to Alois Treindl.)
Release 2019b - 2019-07-01 00:09:53 -0700
Briefly:
Brazil no longer observes DST.
'zic -b slim' outputs smaller TZif files; please try it out.
Palestine's 2019 spring-forward transition was on 03-29, not 03-30.
Changes to future timestamps
Brazil has canceled DST and will stay on standard time indefinitely.
(Thanks to Steffen Thorsen, Marcus Diniz, and Daniel Soares de
Oliveira.)
Predictions for Morocco now go through 2087 instead of 2037, to
work around a problem on newlib when using TZif files output by
zic 2019a or earlier. (Problem reported by David Gauchard.)
Changes to past and future timestamps
Palestine's 2019 spring transition was 03-29 at 00:00, not 03-30
at 01:00. (Thanks to Sharef Mustafa and Even Scharning.) Guess
future transitions to be March's last Friday at 00:00.
Changes to past timestamps
Hong Kong's 1941-06-15 spring-forward transition was at 03:00, not
03:30. Its 1945 transition from JST to HKT was on 11-18 at 02:00,
not 09-15 at 00:00. In 1946 its spring-forward transition was on
04-21 at 00:00, not the previous day at 03:30. From 1946 through
1952 its fall-back transitions occurred at 04:30, not at 03:30.
In 1947 its fall-back transition was on 11-30, not 12-30.
(Thanks to P Chan.)
Changes to past time zone abbreviations
Italy's 1866 transition to Rome Mean Time was on December 12, not
September 22. This affects only the time zone abbreviation for
Europe/Rome between those dates. (Thanks to Stephen Trainor and
Luigi Rosa.)
Changes affecting metadata only
Add info about the Crimea situation in zone1970.tab and zone.tab.
(Problem reported by Serhii Demediuk.)
Changes to code
zic's new -b option supports a way to control data bloat and to
test for year-2038 bugs in software that reads TZif files.
'zic -b fat' and 'zic -b slim' generate larger and smaller output;
for example, changing from fat to slim shrinks the Europe/London
file from 3648 to 1599 bytes, saving about 56%. Fat and slim
files represent the same set of timestamps and use the same TZif
format as documented in tzfile(5) and in Internet RFC 8536.
Fat format attempts to work around bugs or incompatibilities in
older software, notably software that mishandles 64-bit TZif data
or uses obsolete TZ strings like "EET-2EEST" that lack DST rules.
Slim format is more efficient and does not work around 64-bit bugs
or obsolete TZ strings. Currently zic defaults to fat format
unless you compile with -DZIC_BLOAT_DEFAULT=\"slim\"; this
out-of-the-box default is intended to change in future releases
as the buggy software often mishandles timestamps anyway.
zic no longer treats a set of rules ending in 2037 specially.
Previously, zic assumed that such a ruleset meant that future
timestamps could not be predicted, and therefore omitted a
POSIX-like TZ string in the TZif output. The old behavior is no
longer needed for current tzdata, and caused problems with newlib
when used with older tzdata (reported by David Gauchard).
zic no longer generates some artifact transitions. For example,
Europe/London no longer has a no-op transition in January 1996.
Changes to build procedure
tzdata.zi now assumes zic 2017c or later. This shrinks tzdata.zi
by a percent or so.
Changes to documentation and commentary
The Makefile now documents the POSIXRULES macro as being obsolete,
and similarly, zic's -p POSIXRULES option is now documented as
being obsolete. Although the POSIXRULES feature still exists and
works as before, in practice it is rarely used for its intended
purpose, and it does not work either in the default reference
implementation (for timestamps after 2037) or in common
implementations such as GNU/Linux (for contemporary timestamps).
Since POSIXRULES was designed primarily as a temporary transition
facility for System V platforms that died off decades ago, it is
being decommissioned rather than institutionalized.
New info on Bonin Islands and Marcus (thanks to Wakaba and Phake Nick).
Release 2019a - 2019-03-25 22:01:33 -0700
Briefly:
Palestine "springs forward" on 2019-03-30 instead of 2019-03-23.
Metlakatla "fell back" to rejoin Alaska Time on 2019-01-20 at 02:00.
Changes to past and future timestamps
Palestine will not start DST until 2019-03-30, instead of 2019-03-23 as
previously predicted. Adjust our prediction by guessing that spring
transitions will be between 24 and 30 March, which matches recent practice
since 2016. (Thanks to Even Scharning and Tim Parenti.)
Metlakatla ended its observance of Pacific standard time,
rejoining Alaska Time, on 2019-01-20 at 02:00. (Thanks to Ryan
Stanley and Tim Parenti.)
Changes to past timestamps
Israel observed DST in 1980 (08-02/09-13) and 1984 (05-05/08-25).
(Thanks to Alois Treindl and Isaac Starkman.)
Changes to time zone abbreviations
Etc/UCT is now a backward-compatibility link to Etc/UTC, instead
of being a separate zone that generates the abbreviation "UCT",
which nowadays is typically a typo. (Problem reported by Isiah
Meadows.)
Changes to code
zic now has an -r option to limit the time range of output data.
For example, 'zic -r @1000000000' limits the output data to
timestamps starting 1000000000 seconds after the Epoch.
This helps shrink output size and can be useful for applications
not needing the full timestamp history, such as TZDIST truncation;
see Internet RFC 8536 section 5.1. (Inspired by a feature request
from Christopher Wong, helped along by bug reports from Wong and
from Tim Parenti.)
Changes to documentation
Mention Internet RFC 8536 (February 2019), which documents TZif.
tz-link.html now cites tzdata-meta
<https://tzdata-meta.timtimeonline.com/>.
Release 2018i - 2018-12-30 11:05:43 -0800
Briefly:
São Tomé and Príncipe switches from +01 to +00 on 2019-01-01.
Changes to future timestamps
Due to a change in government, São Tomé and Príncipe switches back
from +01 to +00 on 2019-01-01 at 02:00. (Thanks to Vadim
Nasardinov and Michael Deckers.)
Release 2018h - 2018-12-23 17:59:32 -0800
Briefly:
Qyzylorda, Kazakhstan moved from +06 to +05 on 2018-12-21.
New zone Asia/Qostanay because Qostanay, Kazakhstan didn't move.
Metlakatla, Alaska observes PST this winter only.
Guess Morocco will continue to adjust clocks around Ramadan.
Add predictions for Iran from 2038 through 2090.
Changes to future timestamps
Guess that Morocco will continue to fall back just before and
spring forward just after Ramadan, the practice since 2012.
(Thanks to Maamar Abdelkader.) This means Morocco will observe
negative DST during Ramadan in main and vanguard formats, and in
rearguard format it stays in the +00 timezone and observes
ordinary DST in all months other than Ramadan. As before, extend
this guesswork to the year 2037. As a consequence, Morocco is
scheduled to observe three DST transitions in some Gregorian years
(e.g., 2033) due to the mismatch between the Gregorian and Islamic
calendars.
The table of exact transitions for Iranian DST has been extended.
It formerly cut off before the year 2038 in a nod to 32-bit time_t.
It now cuts off before 2091 as there is doubt about how the Persian
calendar will treat 2091. This change predicts DST transitions in
2038-9, 2042-3, and 2046-7 to occur one day later than previously
predicted. As before, post-cutoff transitions are approximated.
Changes to past and future timestamps
Qyzylorda (aka Kyzylorda) oblast in Kazakhstan moved from +06 to
+05 on 2018-12-21. This is a zone split as Qostanay (aka
Kostanay) did not switch, so create a zone Asia/Qostanay.
Metlakatla moved from Alaska to Pacific standard time on 2018-11-04.
It did not change clocks that day and remains on -08 this winter.
(Thanks to Ryan Stanley.) It will revert to the usual Alaska
rules next spring, so this change affects only timestamps
from 2018-11-04 through 2019-03-10.
Change to past timestamps
Kwajalein's 1993-08-20 transition from -12 to +12 was at 24:00,
not 00:00. I transcribed the time incorrectly from Shanks.
(Thanks to Phake Nick.)
Nauru's 1979 transition was on 02-10 at 02:00, not 05-01 at 00:00.
(Thanks to Phake Nick.)
Guam observed DST irregularly from 1959 through 1977.
(Thanks to Phake Nick.)
Hong Kong observed DST in 1941 starting 06-15 (not 04-01), then on
10-01 changed standard time to +08:30 (not +08). Its transition
back to +08 after WWII was on 1945-09-15, not the previous day.
Its 1904-10-30 change took effect at 01:00 +08 (not 00:00 LMT).
(Thanks to Phake Nick, Steve Allen, and Joseph Myers.) Also,
its 1952 fallback was on 11-02 (not 10-25).
This release contains many changes to timestamps before 1946 due
to Japanese possession or occupation of Pacific/Chuuk,
Pacific/Guam, Pacific/Kosrae, Pacific/Kwajalein, Pacific/Majuro,
Pacific/Nauru, Pacific/Palau, and Pacific/Pohnpei.
(Thanks to Phake Nick.)
Assume that the Spanish East Indies was like the Philippines and
observed American time until the end of 1844. This affects
Pacific/Chuuk, Pacific/Kosrae, Pacific/Palau, and Pacific/Pohnpei.
Changes to past tm_isdst flags
For the recent Morocco change, the tm_isdst flag should be 1 from
2018-10-27 00:00 to 2018-10-28 03:00. (Thanks to Michael Deckers.)
Give a URL to the official decree. (Thanks to Matt Johnson.)
Release 2018g - 2018-10-26 22:22:45 -0700
Briefly:
Morocco switches to permanent +01 on 2018-10-28.
Changes to future timestamps
Morocco switches from +00/+01 to permanent +01 effective 2018-10-28,
so its clocks will not fall back as previously scheduled.
(Thanks to Mohamed Essedik Najd and Brian Inglis.)
Changes to code
When generating TZif files with leap seconds, zic no longer uses a
format that trips up older 32-bit clients, fixing a bug introduced
in 2018f. (Reported by Daniel Fischer.) Also, the zic workaround
for QTBUG-53071 now also works for TZif files with leap seconds.
The translator to rearguard format now rewrites the line
"Rule Japan 1948 1951 - Sep Sat>=8 25:00 0 S" to
"Rule Japan 1948 1951 - Sep Sun>=9 1:00 0 S".
This caters to zic before 2007 and to Oracle TZUpdater 2.2.0
and earlier. (Reported by Christos Zoulas.)
Changes to past time zone abbreviations
Change HDT to HWT/HPT for WWII-era abbreviations in Hawaii.
This reverts to 2011h, as the abbreviation change in 2011i was
likely inadvertent.
Changes to documentation
tzfile.5 has new sections on interoperability issues.
Release 2018f - 2018-10-18 00:14:18 -0700
Briefly:
Volgograd moves from +03 to +04 on 2018-10-28.
Fiji ends DST 2019-01-13, not 2019-01-20.
Most of Chile changes DST dates, effective 2019-04-06.
Changes to future timestamps
Volgograd moves from +03 to +04 on 2018-10-28 at 02:00.
(Thanks to Alexander Fetisov and Stepan Golosunov.)
Fiji ends DST 2019-01-13 instead of the 2019-01-20 previously
predicted. (Thanks to Raymond Kumar.) Adjust future predictions
accordingly.
Most of Chile will end DST on the first Saturday in April at 24:00 mainland
time, and resume DST on the first Saturday in September at 24:00 mainland
time. The changes are effective from 2019-04-06, and do not affect the
Magallanes region modeled by America/Punta_Arenas. (Thanks to Juan Correa
and Tim Parenti.) Adjust future predictions accordingly.
Changes to past timestamps
The 2018-05-05 North Korea 30-minute time zone change took place
at 23:30 the previous day, not at 00:00 that day.
China's 1988 spring-forward transition was on April 17, not
April 10. Its DST transitions in 1986/91 were at 02:00, not 00:00.
(Thanks to P Chan.)
Fix several issues for Macau before 1992. Macau's pre-1904 LMT
was off by 10 s. Macau switched to +08 in 1904 not 1912, and
temporarily switched to +09/+10 during World War II. Macau
observed DST in 1942/79, not 1961/80, and there were several
errors for transition times and dates. (Thanks to P Chan.)
The 1948-1951 fallback transitions in Japan were at 25:00 on
September's second Saturday, not at 24:00. (Thanks to Phake Nick.)
zic turns this into 01:00 on the day after September's second
Saturday, which is the best that POSIX or C platforms can do.
Incorporate 1940-1949 Asia/Shanghai DST transitions from a 2014
paper by Li Yu, replacing more-questionable data from Shanks.
Changes to time zone abbreviations
Use "PST" and "PDT" for Philippine time. (Thanks to Paul Goyette.)
Changes to code
zic now always generates TZif files where time type 0 is used for
timestamps before the first transition. This simplifies the
reading of TZif files and should not affect behavior of existing
TZif readers because the same set of time types is used; only
their internal indexes may have changed. This affects only the
legacy zones EST5EDT, CST6CDT, MST7MDT, PST8PDT, CET, MET, and
EET, which previously used nonzero types for these timestamps.
Because of the type 0 change, zic no longer outputs a dummy
transition at time -2**59 (before the Big Bang), as clients should
no longer need this to handle historical timestamps correctly.
This reverts a change introduced in 2013d and shrinks most TZif
files by a few bytes.
zic now supports negative time-of-day in Rule and Leap lines, e.g.,
"Rule X min max - Apr lastSun -6:00 1:00 -" means the transition
occurs at 18:00 on the Saturday before the last Sunday in April.
This behavior was documented in 2018a but the code did not
entirely match the documentation.
localtime.c no longer requires at least one time type in TZif
files that lack transitions or have a POSIX-style TZ string. This
future-proofs the code against possible future extensions to the
format that would allow TZif files with POSIX-style TZ strings and
without transitions or time types.
A read-access subscript error in localtime.c has been fixed.
It could occur only in TZif files with timecnt == 0, something that
does not happen in practice now but could happen in future versions.
localtime.c no longer ignores TZif POSIX-style TZ strings that
specify only standard time. Instead, these TZ strings now
override the default time type for timestamps after the last
transition (or for all timestamps if there are no transitions),
just as DST strings specifying DST have always done.
leapseconds.awk now outputs "#updated" and "#expires" comments,
and supports leap seconds at the ends of months other than June
and December. (Inspired by suggestions from Chris Woodbury.)
Changes to documentation
New restrictions: A Rule name must start with a character that
is neither an ASCII digit nor "-" nor "+", and an unquoted name
should not use characters in the set "!$%&'()*,/:;<=>?@[\]^`{|}~".
The latter restriction makes room for future extensions (a
possibility noted by Tom Lane).
tzfile.5 now documents what time types apply before the first and
after the last transition, if any.
Documentation now uses the spelling "timezone" for a TZ setting
that determines timestamp history, and "time zone" for a
geographic region currently sharing the same standard time.
The name "TZif" is now used for the tz binary data format.
tz-link.htm now mentions the A0 TimeZone Migration utilities.
(Thanks to Aldrin Martoq for the link.)
Changes to build procedure
New 'make' target 'rearguard_tarballs' to build the rearguard
tarball only. This is a convenience on platforms that lack lzip
if you want to build the rearguard tarball. (Problem reported by
Deborah Goldsmith.)
tzdata.zi is now more stable from release to release. (Problem
noted by Tom Lane.) It is also a bit shorter.
tzdata.zi now can contain comment lines documenting configuration
information, such as which data format was selected, which input
files were used, and how leap seconds are treated. (Problems
noted by Lester Caine and Brian Inglis.) If the Makefile defaults
are used these comment lines are absent, for backward
compatibility. A redistributor intending to alter its copy of the
files should also append "-LABEL" to the 'version' file's first
line, where "LABEL" identifies the redistributor's change.
Release 2018e - 2018-05-01 23:42:51 -0700
Briefly:
North Korea switches back to +09 on 2018-05-05.
The main format uses negative DST again, for Ireland etc.
'make tarballs' now also builds a rearguard tarball.
New 's' and 'd' suffixes in SAVE columns of Rule and Zone lines.
Changes to past and future timestamps
North Korea switches back from +0830 to +09 on 2018-05-05.
(Thanks to Kang Seonghoon, Arthur David Olson, Seo Sanghyeon,
and Tim Parenti.)