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[PROPOSED] More clarification/explanation from RFC 8536
by Paul Eggert June 18, 2019

June 18, 2019

This just changes documentation: it does not change code or data. Mostly, it just adopts more terminology from RFC 8536. It also contains an example of what the std/wall and UT/local indicators are for. * newtzset.3, theory.html, tz-how-to.html, tzfile.5, tzfile.h, zic.8: In documentation and comments, make it clearer that local time equals wall clock time. * tzfile.5, tzfile.h: In documentation and comments, say that when isut is 1, isstd must also be 1. * tzfile.5: Specify that bytes are 8 bits, that binary integers use two's complement, and that booleans use 0 and 1. Say that UT offsets are never equal to -2**31, and that they realistically are in the range [-89999, 93599]. Say that leap second counts are signed. Say why std/wall and UT/local indicators are present, and give AKST9AKDT as an example. Do not say that the first standard-time ttinfo is used by localtime, as the actual heuristic is far more complicated; instead, document what RFC 8536 says as what's normally used. * zic.c (struct rule): Adjust comments. --- newtzset.3 | 4 ++-- theory.html | 10 ++++---- tz-how-to.html | 14 ++++++------ tzfile.5 | 62 +++++++++++++++++++++++++++++++++----------------- tzfile.h | 15 ++++++------ zic.8 | 16 ++++++------- zic.c | 6 ++--- 7 files changed, 73 insertions(+), 54 deletions(-) diff --git a/newtzset.3 b/newtzset.3 index 29e8a21..4959851 100644 --- a/newtzset.3 +++ b/newtzset.3 @@ -65,8 +65,8 @@ falls back on Universal Time (UT). .PP If .B TZ -is null, the best available approximation to local wall -clock time, as specified by the +is null, the best available approximation to local (wall +clock) time, as specified by the .IR tzfile (5)-format file .B localtime diff --git a/theory.html b/theory.html index e580ccc..61d556b 100644 --- a/theory.html +++ b/theory.html @@ -955,7 +955,7 @@ an older <code>zic</code>. </li> <li> In POSIX, there is no tamper-proof way for a process to learn the - system's best idea of local wall clock. + system's best idea of local (wall clock) time. This is important for applications that an administrator wants used only at certain times – without regard to whether the user has fiddled the @@ -1052,14 +1052,14 @@ an older <code>zic</code>. </li> <li> A function <code>tzsetwall</code> has been added to arrange for the - system's best approximation to local wall clock time to be delivered + system's best approximation to local (wall clock) time to be delivered by subsequent calls to <code>localtime</code>. - Source code for portable applications that "must" run on local wall - clock time should call <code>tzsetwall</code>; + Source code for portable applications that "must" run on local + time should call <code>tzsetwall</code>; if such code is moved to "old" systems that do not provide <code>tzsetwall</code>, you will not be able to generate an executable program. - (These functions also arrange for local wall clock time to + (These functions also arrange for local time to be used if <code>tzset</code> is called – directly or indirectly – and there is no <code>TZ</code> environment variable; portable applications should not, however, rely on this diff --git a/tz-how-to.html b/tz-how-to.html index 7274af4..2e4842d 100644 --- a/tz-how-to.html +++ b/tz-how-to.html @@ -102,7 +102,7 @@ in some localizable way. It’s used in the file, <code>pacificnew</code>, to determine whether a given year will have a US presidential election; but everything related to that use is commented out.) -<p>The <code>SAVE</code> column contains the wall clock offset from +<p>The <code>SAVE</code> column contains the local (wall clock) offset from local standard time. This is usually either zero for standard time or one hour for daylight saving time; but there’s no reason, in principle, why it can’t @@ -250,10 +250,10 @@ Rule US 2007 max - Nov Sun>=1 2:00 0 S <p>There are two interesting things to note here.</p> <p>First, the time that something happens (in the <code>AT</code> -column) is not necessarily the local wall clock time. The time can be +column) is not necessarily the local (wall clock) time. The time can be suffixed with ‘s’ (for “standard”) to mean -local standard time (different from wall clock time when observing -daylight saving time); or it can be suffixed with ‘g’, +local standard time, different from local (wall clock) time when observing +daylight saving time; or it can be suffixed with ‘g’, ‘u’, or ‘z’, all three of which mean the standard time at the <a href="https://en.wikipedia.org/wiki/Prime_Meridian">prime meridian</a>. @@ -265,8 +265,8 @@ href="https://en.wikipedia.org/wiki/Coordinated_Universal_Time">UTC</a>” (whichever was official at the time); ‘z’ stands for the <a href="https://en.wikipedia.org/wiki/Nautical_time">nautical time zone</a> Z (a.k.a. “Zulu” which, in turn, stands for ‘Z’). -The time can also be suffixed with ‘w’ meaning “wall -clock time;” but it usually isn’t because that’s the +The time can also be suffixed with ‘w’ meaning local (wall +clock) time; but it usually isn’t because that’s the default.</p> <p>Second, the day in the <code>ON</code> column, in addition to @@ -467,7 +467,7 @@ Zone Pacific/Honolulu ... 1933 Apr 30 2:00 <p>Hawaii tried daylight saving time for three weeks in 1933 and decided they didn’t like it. <code>8-) </code>Note that the <code>STDOFF</code> column always contains the standard time -offset, so the wall clock time during this period was GMT − +offset, so the local (wall clock) time during this period was GMT − 10:30 + 1:00 = GMT − 9:30.</p> <p>The <code>FORMAT</code> column specifies the usual abbreviation of diff --git a/tzfile.5 b/tzfile.5 index b591e56..d13029c 100644 --- a/tzfile.5 +++ b/tzfile.5 @@ -16,6 +16,13 @@ The timezone information files used by are typically found under a directory with a name like .IR /usr/share/zoneinfo . These files use the format described in Internet RFC 8536. +Each file is a sequence of 8-bit bytes. +In a file, a binary integer is represented by a sequence of one or +more bytes in network order (bigendian, or high-order byte first), +with all bits significant, +a signed binary integer is represented using two's complement, +and a boolean is represented by a one-byte binary integer that is +either 0 (false) or 1 (true). The format begins with a 44-byte header containing the following fields: .IP * 2 The magic four-byte ASCII sequence @@ -30,11 +37,7 @@ or .IP * Fifteen bytes containing zeros reserved for future use. .IP * -Six four-byte integer values -written in a standard byte order -(the high-order byte of the value is written first). -These values are, -in order: +Six four-byte integer values, in the following order: .RS .TP .I tzh_ttisutcnt @@ -64,7 +67,7 @@ depend on the contents of the header: .IP * 2 .I tzh_timecnt four-byte signed integer values sorted in ascending order. -These values are written in standard byte order. +These values are written in network byte order. Each is used as a transition time (as returned by .BR time (2)) at which the rules for computing local time change. @@ -96,7 +99,7 @@ struct ttinfo { .sp Each structure is written as a four-byte signed integer value for .IR tt_utoff , -in a standard byte order, followed by a one-byte value for +in network byte order, followed by a one-byte boolean for .I tt_isdst and a one-byte value for .IR tt_desigidx . @@ -114,14 +117,23 @@ serves as an index into the array of time zone abbreviation bytes that follow the .I ttinfo structure(s) in the file. +The +.I tt_utoff +value is never equal to -2**31, to let 32-bit clients negate it without +overflow. +Also, in realistic applications +.I tt_utoff +is in the range [-89999, 93599] (i.e., more than -25 hours and less +than 26 hours); this allows easy support by implementations that +already support the POSIX-required range [-24:59:59, 25:59:59]. .IP * .I tzh_leapcnt -pairs of four-byte values, written in standard byte order; +pairs of four-byte values, written in network byte order; the first value of each pair gives the nonnegative time (as returned by .BR time (2)) at which a leap second occurs; -the second gives the +the second is a signed integer specifying the .I total number of leap seconds to be applied during the time period starting at the given time. @@ -130,28 +142,36 @@ Each transition is for one leap second, either positive or negative; transitions always separated by at least 28 days minus 1 second. .IP * .I tzh_ttisstdcnt -standard/wall indicators, each stored as a one-byte value; +standard/wall indicators, each stored as a one-byte boolean; they tell whether the transition times associated with local time types -were specified as standard time or wall clock time, -and are used when a timezone file is used in handling POSIX-style -timezone environment variables. +were specified as standard time or local (wall clock) time. .IP * .I tzh_ttisutcnt -UT/local indicators, each stored as a one-byte value; +UT/local indicators, each stored as a one-byte boolean; they tell whether the transition times associated with local time types -were specified as UT or local time, -and are used when a timezone file is used in handling POSIX-style -timezone environment variables. +were specified as UT or local time. +If a UT/local indicator is set, the corresponding standard/wall indicator +must also be set. +.PP +The standard/wall and UT/local indicators were designed for +transforming a TZif file's transition times into transitions appropriate +for another time zone specified via a POSIX-style TZ string that lacks rules. +For example, when TZ="AKST9AKDT" and there is no TZif file "AKST9AKDT", +the transition times might be adapted from a TZif file with the +well-known name "posixrules" that is present only for this purpose and +is a copy of the file "America/New_York", a file with a different UT offset. +POSIX does not specify this obsolescent transformational behavior and +widely used platforms such as GNU/Linux do not support it correctly, so users +desiring Alaska time should specify TZ="America/Anchorage" for better +historical coverage, or TZ="AKST9AKDT,M3.2.0,M11.1.0" for POSIX +conformance and coverage for recent timestamps only. .PP The .BR localtime (3) function -uses the first standard-time +normally uses the first .I ttinfo structure in the file -(or simply the first -.I ttinfo -structure in the absence of a standard-time structure) if either .I tzh_timecnt is zero or the time argument is less than the first transition time recorded diff --git a/tzfile.h b/tzfile.h index 52673d6..ee91104 100644 --- a/tzfile.h +++ b/tzfile.h @@ -69,14 +69,15 @@ struct tzhead { ** one (char [4]) total correction after above ** tzh_ttisstdcnt (char)s indexed by type; if 1, transition ** time is standard time, if 0, -** transition time is wall clock time -** if absent, transition times are -** assumed to be wall clock time -** tzh_ttisutcnt (char)s indexed by type; if 1, transition -** time is UT, if 0, -** transition time is local time -** if absent, transition times are +** transition time is local (wall clock) +** time; if absent, transition times are ** assumed to be local time +** tzh_ttisutcnt (char)s indexed by type; if 1, transition +** time is UT, if 0, transition time is +** local time; if absent, transition +** times are assumed to be local time. +** When this is 1, the corresponding +** std/wall indicator must also be 1. */ /* diff --git a/zic.8 b/zic.8 index 02b6048..3a4d96f 100644 --- a/zic.8 +++ b/zic.8 @@ -385,13 +385,12 @@ to other applications requiring greater precision. The source format does not specify any maximum precision. Any of these forms may be followed by the letter .B w -if the given time is local +if the given time is local or .q "wall clock" time, .B s -if the given time is local -.q "standard" -time, or +if the given time is standard time without any adjustment for daylight saving, +or .B u (or .B g @@ -399,7 +398,7 @@ or .BR z ) if the given time is universal time; in the absence of an indicator, -wall clock time is assumed. +local (wall clock) time is assumed. These forms ignore leap seconds; for example, if a leap second occurs at 00:59:60 local time, .q "1:00" @@ -478,7 +477,8 @@ a file name component is a maximal substring that does not contain .q "/" . .TP .B STDOFF -The amount of time to add to UT to get standard time. +The amount of time to add to UT to get standard time, +without any adjustment for daylight saving. This field has the same format as the .B AT and @@ -636,7 +636,7 @@ or (an abbreviation of) .q "Rolling" if the leap second time given by the other fields should be interpreted as -local wall clock time. +local (wall clock) time. .SH "EXTENDED EXAMPLE" Here is an extended example of .B zic @@ -720,7 +720,7 @@ coincides with and is equal to a clock retreat caused by a change in UT offset, .B zic produces a single transition to daylight saving at the new UT offset -(without any change in wall clock time). +without any change in local (wall clock) time. To get separate transitions use multiple zone continuation lines specifying transition instants using universal time. diff --git a/zic.c b/zic.c index b3665bd..3fb32c7 100644 --- a/zic.c +++ b/zic.c @@ -92,10 +92,8 @@ struct rule { int r_wday; zic_t r_tod; /* time from midnight */ - bool r_todisstd; /* above is standard time if 1 */ - /* or wall clock time if 0 */ - bool r_todisut; /* above is GMT if 1 */ - /* or local time if 0 */ + bool r_todisstd; /* is r_tod standard time? */ + bool r_todisut; /* is r_tod UT? */ bool r_isdst; /* is this daylight saving time? */ zic_t r_save; /* offset from standard time */ const char * r_abbrvar; /* variable part of abbreviation */ -- 2.21.0

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[PROPOSED] Fix 'zic -b slim' bug with TZ='CET'
by Paul Eggert June 15, 2019

June 15, 2019

Without this fix, 'zic -b slim' can mishandle transitions in the few obsolescent zones like CET that do not start with local mean time. For example, for CET it incorrectly optimizes away the first and third transitions, and treats the second transition as one to standard time instead of to DST. * zic.c (swaptypes): Remove. All uses removed. (writezone): Swap indices rather than contents of the old type 0 and the new (default) type 0 array entries. --- zic.c | 44 +++++++++++++++++++------------------------- 1 file changed, 19 insertions(+), 25 deletions(-) diff --git a/zic.c b/zic.c index 34228a5..03f33ee 100644 --- a/zic.c +++ b/zic.c @@ -1810,17 +1810,6 @@ atcomp(const void *avp, const void *bvp) return (a < b) ? -1 : (a > b); } -static void -swaptypes(int i, int j) -{ - { zic_t t = gmtoffs[i]; gmtoffs[i] = gmtoffs[j]; gmtoffs[j] = t; } - { char t = isdsts[i]; isdsts[i] = isdsts[j]; isdsts[j] = t; } - { unsigned char t = abbrinds[i]; abbrinds[i] = abbrinds[j]; - abbrinds[j] = t; } - { bool t = ttisstds[i]; ttisstds[i] = ttisstds[j]; ttisstds[j] = t; } - { bool t = ttisgmts[i]; ttisgmts[i] = ttisgmts[j]; ttisgmts[j] = t; } -} - struct timerange { int defaulttype; ptrdiff_t base, count; @@ -2066,7 +2055,6 @@ writezone(const char *const name, const char *const string, char version, THISDEFAULTTYPE appears as type 0 in the output instead of OLD0. TYPEMAP also omits unused types. */ old0 = strlen(omittype); - swaptypes(old0, thisdefaulttype); #ifndef LEAVE_SOME_PRE_2011_SYSTEMS_IN_THE_LURCH /* @@ -2085,12 +2073,16 @@ writezone(const char *const name, const char *const string, char version, if (isdsts[types[i]]) mrudst = types[i]; else mrustd = types[i]; - for (i = old0; i < typecnt; i++) - if (!omittype[i]) { - if (isdsts[i]) - hidst = i; - else histd = i; - } + for (i = old0; i < typecnt; i++) { + int h = (i == old0 ? thisdefaulttype + : i == thisdefaulttype ? old0 : i); + if (!omittype[h]) { + if (isdsts[h]) + hidst = i; + else + histd = i; + } + } if (hidst >= 0 && mrudst >= 0 && hidst != mrudst && gmtoffs[hidst] != gmtoffs[mrudst]) { isdsts[mrudst] = -1; @@ -2204,12 +2196,15 @@ writezone(const char *const name, const char *const string, char version, if (hicut) putc(currenttype, fp); - for (i = old0; i < typecnt; i++) - if (!omittype[i]) { - puttzcode(gmtoffs[i], fp); - putc(isdsts[i], fp); - putc((unsigned char) indmap[abbrinds[i]], fp); - } + for (i = old0; i < typecnt; i++) { + int h = (i == old0 ? thisdefaulttype + : i == thisdefaulttype ? old0 : i); + if (!omittype[h]) { + puttzcode(gmtoffs[h], fp); + putc(isdsts[h], fp); + putc(indmap[abbrinds[h]], fp); + } + } if (thischarcnt != 0) fwrite(thischars, sizeof thischars[0], thischarcnt, fp); @@ -2244,7 +2239,6 @@ writezone(const char *const name, const char *const string, char version, for (i = old0; i < typecnt; i++) if (!omittype[i]) putc(ttisgmts[i], fp); - swaptypes(old0, thisdefaulttype); } fprintf(fp, "\n%s\n", string); close_file(fp, directory, name); -- 2.21.0

1 0

[PROPOSED] * NEWS: Mention -b slim briefly.
by Paul Eggert June 14, 2019

June 14, 2019

--- NEWS | 1 + 1 file changed, 1 insertion(+) diff --git a/NEWS b/NEWS index 0e4c688..7aaae11 100644 --- a/NEWS +++ b/NEWS @@ -4,6 +4,7 @@ Unreleased, experimental changes 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 -- 2.21.0

1 0

[PROPOSED 1/3] Tune and simplify addtype
by Paul Eggert June 14, 2019

June 14, 2019

* zic.c (addtype): Avoid the need to call strcmp each time through the loop checking for duplicate zone types. The strcmp is unnecessary if we already have checked for duplicate abbreviations and so can just look at the strings’ offsets. So, look for those duplicates first. --- zic.c | 36 +++++++++++++++++++----------------- 1 file changed, 19 insertions(+), 17 deletions(-) diff --git a/zic.c b/zic.c index 2cd8cc7..3e27a48 100644 --- a/zic.c +++ b/zic.c @@ -2876,16 +2876,28 @@ addtype(zic_t gmtoff, char const *abbr, bool isdst, bool ttisstd, bool ttisgmt) { register int i, j; - /* - ** See if there's already an entry for this zone type. - ** If so, just return its index. - */ - for (i = 0; i < typecnt; ++i) { + if (! (-1L - 2147483647L <= gmtoff && gmtoff <= 2147483647L)) { + error(_("UT offset out of range")); + exit(EXIT_FAILURE); + } + + for (j = 0; j < charcnt; ++j) + if (strcmp(&chars[j], abbr) == 0) + break; + if (j == charcnt) + newabbr(abbr); + else { + /* + ** See if there's already an entry for this zone type. + ** If so, just return its index. + */ + for (i = 0; i < typecnt; i++) { if (gmtoff == gmtoffs[i] && isdst == isdsts[i] && - strcmp(abbr, &chars[abbrinds[i]]) == 0 && + j == abbrinds[i] && ttisstd == ttisstds[i] && ttisgmt == ttisgmts[i]) return i; + } } /* ** There isn't one; add a new one, unless there are already too @@ -2895,22 +2907,12 @@ addtype(zic_t gmtoff, char const *abbr, bool isdst, bool ttisstd, bool ttisgmt) error(_("too many local time types")); exit(EXIT_FAILURE); } - if (! (-1L - 2147483647L <= gmtoff && gmtoff <= 2147483647L)) { - error(_("UT offset out of range")); - exit(EXIT_FAILURE); - } + i = typecnt++; gmtoffs[i] = gmtoff; isdsts[i] = isdst; ttisstds[i] = ttisstd; ttisgmts[i] = ttisgmt; - - for (j = 0; j < charcnt; ++j) - if (strcmp(&chars[j], abbr) == 0) - break; - if (j == charcnt) - newabbr(abbr); abbrinds[i] = j; - ++typecnt; return i; } -- 2.21.0

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UTC calculation for March 12, 3001 [IANA #1143241], [PR 9419866]
by Lasher, Beth June 10, 2019

June 10, 2019

In the year 3001, Daylight Savings time is applied on Sunday March 9, 3001 as expected. (Eastern Standard time). BUT on the following Thursday, March 12, 3001 at 3 am, it seems that another Daylight Savings Time change is applied. After March 12, 3001, the UTC time zone offset for Eastern Daylight Savings Time is 3 hours (not 4) and remains that way until the year 9999. Is this correct? What is the cause of this second time offset change?

10 16

[PROPOSED] Cite US DST legislation
by Paul Eggert June 7, 2019

June 7, 2019

* northamerica: Cite all the US federal DST legislation. (US): Adjust table to match the legislation more closely. This does not affect the TZif output files. --- northamerica | 26 ++++++++++++++++++++------ 1 file changed, 20 insertions(+), 6 deletions(-) diff --git a/northamerica b/northamerica index 65827ec..52898de 100644 --- a/northamerica +++ b/northamerica @@ -93,10 +93,24 @@ # was the first nationwide legal time standard, and apparently # time was just called "Standard Time" or "Daylight Saving Time". -# From Arthur David Olson: -# US Daylight Saving Time ended on the last Sunday of *October* in 1974. -# See, for example, the front page of the Saturday, 1974-10-26 -# and Sunday, 1974-10-27 editions of the Washington Post. +# From Paul Eggert (2019-06-04): +# Here is the legal basis for the US federal rules. +# * Public Law 65-107 (1918-03-19) implemented standard and daylight saving +# time for the first time across the US, springing forward on March's last +# Sunday and falling back on October's last Sunday. +# * Public Law 66-40 (1919-08-20) repealed DST on October 1919's last Sunday. +# * Public Law 77-403 (1942-01-20) started wartime DST on 1942-02-09. +# * Public Law 79-187 (1945-09-25) ended wartime DST on 1945-09-30. +# * Public Law 89-387 (1966-04-13) reinstituted a national standard for DST, +# from April's last Sunday to October's last Sunday, effective 1967. +# * Public Law 93-182 (1973-12-15) moved the 1974 spring-forward to 01-06. +# * Public Law 94-434 (1974-10-05) moved the 1975 spring-forward to +# February's last Sunday. +# * Public Law 99-359 (1986-07-08) moved the spring-forward to April's first +# Sunday. +# * Public Law 109-50 (2005-08-08), effective 2007, moved the spring-forward +# to March's second Sunday and the fall-back to November's first Sunday. +# All transitions are at 02:00 local time. # From Arthur David Olson: # Before the Uniform Time Act of 1966 took effect in 1967, observance of @@ -152,11 +166,11 @@ Rule US 1918 1919 - Mar lastSun 2:00 1:00 D Rule US 1918 1919 - Oct lastSun 2:00 0 S Rule US 1942 only - Feb 9 2:00 1:00 W # War Rule US 1945 only - Aug 14 23:00u 1:00 P # Peace -Rule US 1945 only - Sep lastSun 2:00 0 S +Rule US 1945 only - Sep 30 2:00 0 S Rule US 1967 2006 - Oct lastSun 2:00 0 S Rule US 1967 1973 - Apr lastSun 2:00 1:00 D Rule US 1974 only - Jan 6 2:00 1:00 D -Rule US 1975 only - Feb 23 2:00 1:00 D +Rule US 1975 only - Feb lastSun 2:00 1:00 D Rule US 1976 1986 - Apr lastSun 2:00 1:00 D Rule US 1987 2006 - Apr Sun>=1 2:00 1:00 D Rule US 2007 max - Mar Sun>=8 2:00 1:00 D -- 2.21.0

5 8

tzdb-latest.tar.gz download issue
by Matt Johnson June 4, 2019

June 4, 2019

The lzip file, https://www.iana.org/time-zones/repository/tzdb-latest.tar.lz redirects to https://data.iana.org/time-zones/tzdb-latest.tar.lz and downloads successfully. The gzip file, https://www.iana.org/time-zones/repository/tzdb-latest.tar.gz redirects to https://data.iana.org/time-zones/tzdb-latest.tar.gz and then fails with a 404. They both used to work, not sure what happened. Thanks, Matt

4 4

Extend POSIX TZ to allow transition times outside 00-24 range, permanent DST
by Paul Eggert June 3, 2019

June 3, 2019

I recently proposed extending the POSIX spec for TZ strings. Please see: http://austingroupbugs.net/view.php?id=1252 This proposal is a modest one, as it doesn't specify TZ strings like 'America/Los_Angeles'. Instead it merely specifies the strings generated by zic and stored into TZif files. This includes strings like '<-03>3<-02>,M3.5.0/-2,M10.5.0/-1' which use times of day outside the 00-24 range, and strings like 'EST5EDT,0/0,J365/25' that represent permanent daylight saving time. This extension to POSIX TZ strings has already been specified in Internet RFC 8536 section 3.3.1 <https://tools.ietf.org/html/rfc8536#page-13> and I think it's a good idea to backport the extension to POSIX itself, as this will bless the common practice of taking the last line of a TZif file and using it as a TZ string on small platforms that lack room to store the TZif files. Please feel free to comment at austingroupbugs.net.

1 0

[PROPOSED] Add an outline to tz-link.html
by Paul Eggert June 1, 2019

June 1, 2019

* tz-link.html: Add an outline, so that it’s more like theory.html. --- tz-link.html | 94 ++++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 92 insertions(+), 2 deletions(-) diff --git a/tz-link.html b/tz-link.html index e0d8cc8..85fc001 100644 --- a/tz-link.html +++ b/tz-link.html @@ -18,6 +18,46 @@ histories and planned futures are often recorded only fitfully. Here is a summary of attempts to organize and record relevant data in this area. </p> + <h3>Outline</h3> + <nav> + <ul> + <li>The <code><abbr>tz</abbr></code> database product and process + <ul> + <li><a href="#tzdb">The <code><abbr>tz</abbr></code> database</a></li> + <li><a href="#download">Downloading the <code><abbr>tz</abbr></code> database</a></li> + <li><a href="#changes">Changes to the <code><abbr>tz</abbr></code> database</a></li> + <li><a href="#commentary">Commentary on the <code><abbr>tz</abbr></code> database</a></li> + </ul> + </li> + <li>Uses of the <code><abbr>tz</abbr></code> database + <ul> + <li><a href="#web">Web sites using recent versions of the <code><abbr>tz</abbr></code> database</a></li> + <li><a href="#protocols">Network protocols for <code><abbr>tz</abbr></code> data</a></li> + <li><a href="#compilers">Other <code><abbr>tz</abbr></code> compilers</a></li> + <li><a href="#TZif">Other <abbr>TZif</abbr> readers</a></li> + <li><a href="#software">Other <code><abbr>tz</abbr></code>-based time zone software</a></li> + </ul> + </li> + <li>Related data + <ul> + <li><a href="#other-dbs">Other time zone databases</a></li> + <li><a href="#maps">Maps</a></li> + <li><a href="#boundaries">Time zone boundaries</a></li> + </ul> + </li> + <li>Timekeeping concepts + <ul> + <li><a href="#civil">Civil time concepts and history</a></li> + <li><a href="#national">National histories of legal time</a></li> + <li><a href="#precision">Precision timekeeping</a></li> + <li><a href="#notation">Time notation</a></li> + <li><a href="#see-also">See also</a></li> + </ul> + </li> + </ul> + </nav> + +<section> <h2 id="tzdb">The <code><abbr title="time zone">tz</abbr></code> database</h2> <p> The <a href="https://en.wikipedia.org/wiki/Public_domain">public-domain</a> @@ -88,6 +128,9 @@ Universal Time</a> (<abbr>UTC</abbr>). The database also records when daylight saving time was in use, along with some time zone abbreviations such as <abbr>EST</abbr> for Eastern Standard Time in the <abbr>US</abbr>.</p> +</section> + +<section> <h2 id="download">Downloading the <code><abbr>tz</abbr></code> database</h2> <p> The following <a @@ -148,6 +191,9 @@ specified by <a href="https://tools.ietf.org/html/8536">Internet The code also lets you read a <abbr>TZif</abbr> file and interpret timestamps for that location.</p> +</section> + +<section> <h2 id="changes">Changes to the <code><abbr>tz</abbr></code> database</h2> <p> The <code><abbr>tz</abbr></code> code and data @@ -226,6 +272,9 @@ found in <a href="theory.html">Theory and pragmatics of the tz code and data</a> <a href="https://a0.github.io/a0-tzmigration/">A0 TimeZone Migration</a> displays changes between recent <code><abbr>tzdb</abbr></code> versions. </p> +</section> + +<section> <h2 id="commentary">Commentary on the <code><abbr>tz</abbr></code> database</h2> <ul> <li>The article @@ -239,6 +288,9 @@ href="https://blog.jonudell.net/2009/10/23/a-literary-appreciation-of-the-olsonz literary appreciation of the Olson/Zoneinfo/tz database</a> comments on the database's style.</li> </ul> +</section> + +<section> <h2 id="web">Web sites using recent versions of the <code><abbr>tz</abbr></code> database</h2> <p> @@ -270,6 +322,9 @@ calculates the current time difference between locations.</li> <li><a href="http://www.wx-now.com">Weather Now</a> and <a href="http://www.thetimenow.com">The Time Now</a> list the weather too.</li> </ul> +</section> + +<section> <h2 id="protocols">Network protocols for <code><abbr>tz</abbr></code> data</h2> <ul> <li>The <a href="https://www.ietf.org">Internet Engineering Task Force</a>'s @@ -302,6 +357,9 @@ title="Extensible Markup Language">XML</abbr></a> format, and a variant uses <a href="https://www.json.org"><abbr title="JavaScript Object Notation">JSON</abbr></a> format.</li> </ul> +</section> + +<section> <h2 id="compilers">Other <code><abbr>tz</abbr></code> compilers</h2> <ul> <li><a href="https://sourceforge.net/projects/vzic/">Vzic</a> is a <a @@ -439,6 +497,9 @@ source into text files, along with a runtime that can read those files. Tcl is freely available under a <abbr>BSD</abbr>-style license.</li> </ul> +</section> + +<section> <h2 id="TZif">Other <abbr>TZif</abbr> readers</h2> <ul> <li>The <a @@ -497,6 +558,9 @@ package contains <a href="https://www.haskell.org">Haskell</a> code that parses and uses <abbr>TZif</abbr> data. It is freely available under a <abbr>BSD</abbr>-style license.</li> </ul> +</section> + +<section> <h2 id="software">Other <code><abbr>tz</abbr></code>-based time zone software</h2> <ul> <li><a href="https://foxclocks.org">FoxClocks</a> @@ -554,6 +618,9 @@ a macOS program. Its developers <a href="http://veladg.com/tzoffer.html">offer free licenses</a> to <code><abbr>tz</abbr></code> contributors.</li> </ul> +</section> + +<section> <h2 id="other-dbs">Other time zone databases</h2> <ul> <li><a href="https://www.astro.com/atlas">Time-zone Atlas</a> @@ -582,6 +649,9 @@ Schedules Information Manual</a> of the International Air Transport Association gives current time zone rules for airports served by commercial aviation.</li> </ul> +</section> + +<section> <h2 id="maps">Maps</h2> <ul> <li>The <a href="https://www.cia.gov/index.html">United States Central @@ -609,6 +679,9 @@ much is time wrong around the world?</a> maps the difference between mean solar and standard time, highlighting areas such as western China where the two differ greatly. It's a bit out of date, unfortunately.</li> </ul> +</section> + +<section> <h2 id="boundaries">Time zone boundaries</h2> <p>Geographical boundaries between timezones are available from several <a href="https://en.wikipedia.org/wiki/Geolocation">geolocation</a> @@ -683,6 +756,9 @@ for land and territorial waters only). A captain can change ship's clocks any time after entering a new time zone; midnight changes are common.</li> </ul> +</section> + +<section> <h2 id="civil">Civil time concepts and history</h2> <ul> <li><a href="https://www.nist.gov/pml/time-and-frequency-division/popular-links/walk-thr…">A @@ -704,6 +780,9 @@ time zone boundary.</li> <li><a href="http://statoids.com/tconcept.html">Basic Time Zone Concepts</a> discusses terminological issues behind time zones.</li> </ul> +</section> + +<section> <h2 id="national">National histories of legal time</h2> <dl> <dt>Australia</dt> @@ -790,6 +869,9 @@ Navy (SOHMA) publishes an annual <a href="http://www.armada.gub.uy/sohma/index.php/servicios/datos-astronomicos" hreflang="es">almanac (in Spanish)</a>.</dd> </dl> +</section> + +<section> <h2 id="precision">Precision timekeeping</h2> <ul> <li><a @@ -878,6 +960,9 @@ without Leap Seconds</a> gives pointers on this contentious issue, which was active until 2015 and could become active again.</li> </ul> +</section> + +<section> <h2 id="notation">Time notation</h2> <ul> <li>The <a id="CLDR" href="http://cldr.unicode.org">Unicode Common Locale Data @@ -946,18 +1031,23 @@ any future changes to the rules. One should never set local time is nine hours ahead of <abbr>UT</abbr> and the time zone is called "<abbr>GMT</abbr>".</li> </ul> +</section> + +<section> <h2 id="see-also">See also</h2> <ul> <li><a href="theory.html">Theory and pragmatics of the tz code and data</a></li> <li><a href="tz-art.html">Time and the Arts</a></li> </ul> +</section> + +<footer> <hr> -<address> This web page is in the public domain, so clarified as of 2009-05-17 by Arthur David Olson. <br> Please send corrections to this web page to the <a href="mailto:tz@iana.org">time zone mailing list</a>. -</address> +</footer> </body> </html> -- 2.17.1

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Hong Kong Time history
by P Chan May 31, 2019

May 31, 2019

*According to the Hong Kong Daylight-Saving Regulations, 1941, the 1941 spring-forward transition was at 03:00. http://sunzi.lib.hku.hk/hkgro/view/g1941/304271.pdf http://sunzi.lib.hku.hk/hkgro/view/g1941/305516.pdf *According to some articles from South China Morning Post, +08 was resumed on 1945-11-18 at 02:00. https://i.imgur.com/M2IsZ3c.png https://i.imgur.com/iOPqrVo.png https://i.imgur.com/fffcGDs.png *Some newspapers published on said the 1946 spring-forward transition was on 04-21 at 00:00. The Kung Sheung Evening News 1946-04-20 (Chinese) https://i.imgur.com/ZSzent0.png https://mmis.hkpl.gov.hk///c/portal/cover?c=QF757YsWv5%2FH7zGe%2FKF%2BFLYsu… p.4 The Kung Sheung Daily News 1946-04-21 (Chinese) https://i.imgur.com/7ecmRlcm.png https://mmis.hkpl.gov.hk///c/portal/cover?c=QF757YsWv5%2BQBGt1%2BwUj5qG2Gqt… p.4 *According to the Summer Time Ordinance (1946), the fallback transitions between 1946 and 1952 were at 03:30 Standard Time (+08) http://oelawhk.lib.hku.hk/archive/files/bb74b06a74d5294620a15de560ab33c6.pdf *Some other laws and regulations related to DST from 1953 to 1979 Summer Time Ordinance 1953 https://i.imgur.com/IOlJMav.jpg Summer Time (Amendment) Ordinance 1965 https://i.imgur.com/8rofeLa.jpg Interpretation and General Clauses Ordinance (1966) https://i.imgur.com/joy3msj.jpg Emergency (Summer Time) Regulation 1973 https://i.imgur.com/OpRWrKz.jpg Interpretation and General Clauses (Amendment) Ordinance 1977 https://i.imgur.com/RaNqnc4.jpg Resolution of the Legislative Council passed on 9 May 1979 https://www.legco.gov.hk/yr78-79/english/lc_sitg/hansard/h790509.pdf#page=39 P Chan

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