diff --git a/external/public-domain/tz/dist/TZDATA_VERSION b/external/public-domain/tz/dist/TZDATA_VERSION index b9b6b8d106cb..5ec975e59eec 100644 --- a/external/public-domain/tz/dist/TZDATA_VERSION +++ b/external/public-domain/tz/dist/TZDATA_VERSION @@ -1 +1 @@ -tzdata-2017b +tzdata-2017c diff --git a/external/public-domain/tz/dist/Theory b/external/public-domain/tz/dist/Theory deleted file mode 100644 index 33e46069ba23..000000000000 --- a/external/public-domain/tz/dist/Theory +++ /dev/null @@ -1,870 +0,0 @@ -Theory and pragmatics of the tz code and data - - ------ Outline ----- - - Scope of the tz database - Names of time zone rules - Time zone abbreviations - Accuracy of the tz database - Time and date functions - Interface stability - Calendrical issues - Time and time zones on Mars - - ------ Scope of the tz database ----- - -The tz database attempts to record the history and predicted future of -all computer-based clocks that track civil time. To represent this -data, the world is partitioned into regions whose clocks all agree -about time stamps that occur after the somewhat-arbitrary cutoff point -of the POSIX Epoch (1970-01-01 00:00:00 UTC). For each such region, -the database records all known clock transitions, and labels the region -with a notable location. Although 1970 is a somewhat-arbitrary -cutoff, there are significant challenges to moving the cutoff earlier -even by a decade or two, due to the wide variety of local practices -before computer timekeeping became prevalent. - -Clock transitions before 1970 are recorded for each such location, -because most systems support time stamps before 1970 and could -misbehave if data entries were omitted for pre-1970 transitions. -However, the database is not designed for and does not suffice for -applications requiring accurate handling of all past times everywhere, -as it would take far too much effort and guesswork to record all -details of pre-1970 civil timekeeping. - -As described below, reference source code for using the tz database is -also available. The tz code is upwards compatible with POSIX, an -international standard for UNIX-like systems. As of this writing, the -current edition of POSIX is: - - The Open Group Base Specifications Issue 7 - IEEE Std 1003.1-2008, 2016 Edition - - - - ------ Names of time zone rules ----- - -Each of the database's time zone rules has a unique name. -Inexperienced users are not expected to select these names unaided. -Distributors should provide documentation and/or a simple selection -interface that explains the names; for one example, see the 'tzselect' -program in the tz code. The Unicode Common Locale Data Repository - contains data that may be useful for other -selection interfaces. - -The time zone rule naming conventions attempt to strike a balance -among the following goals: - - * Uniquely identify every region where clocks have agreed since 1970. - This is essential for the intended use: static clocks keeping local - civil time. - - * Indicate to experts where that region is. - - * Be robust in the presence of political changes. For example, names - of countries are ordinarily not used, to avoid incompatibilities - when countries change their name (e.g. Zaire->Congo) or when - locations change countries (e.g. Hong Kong from UK colony to - China). - - * Be portable to a wide variety of implementations. - - * Use a consistent naming conventions over the entire world. - -Names normally have the form AREA/LOCATION, where AREA is the name -of a continent or ocean, and LOCATION is the name of a specific -location within that region. North and South America share the same -area, 'America'. Typical names are 'Africa/Cairo', 'America/New_York', -and 'Pacific/Honolulu'. - -Here are the general rules used for choosing location names, -in decreasing order of importance: - - Use only valid POSIX file name components (i.e., the parts of - names other than '/'). Do not use the file name - components '.' and '..'. Within a file name component, - use only ASCII letters, '.', '-' and '_'. Do not use - digits, as that might create an ambiguity with POSIX - TZ strings. A file name component must not exceed 14 - characters or start with '-'. E.g., prefer 'Brunei' - to 'Bandar_Seri_Begawan'. Exceptions: see the discussion - of legacy names below. - A name must not be empty, or contain '//', or start or end with '/'. - Do not use names that differ only in case. Although the reference - implementation is case-sensitive, some other implementations - are not, and they would mishandle names differing only in case. - If one name A is an initial prefix of another name AB (ignoring case), - then B must not start with '/', as a regular file cannot have - the same name as a directory in POSIX. For example, - 'America/New_York' precludes 'America/New_York/Bronx'. - Uninhabited regions like the North Pole and Bouvet Island - do not need locations, since local time is not defined there. - There should typically be at least one name for each ISO 3166-1 - officially assigned two-letter code for an inhabited country - or territory. - If all the clocks in a region have agreed since 1970, - don't bother to include more than one location - even if subregions' clocks disagreed before 1970. - Otherwise these tables would become annoyingly large. - If a name is ambiguous, use a less ambiguous alternative; - e.g. many cities are named San José and Georgetown, so - prefer 'Costa_Rica' to 'San_Jose' and 'Guyana' to 'Georgetown'. - Keep locations compact. Use cities or small islands, not countries - or regions, so that any future time zone changes do not split - locations into different time zones. E.g. prefer 'Paris' - to 'France', since France has had multiple time zones. - Use mainstream English spelling, e.g. prefer 'Rome' to 'Roma', and - prefer 'Athens' to the Greek 'Αθήνα' or the Romanized 'Athína'. - The POSIX file name restrictions encourage this rule. - Use the most populous among locations in a zone, - e.g. prefer 'Shanghai' to 'Beijing'. Among locations with - similar populations, pick the best-known location, - e.g. prefer 'Rome' to 'Milan'. - Use the singular form, e.g. prefer 'Canary' to 'Canaries'. - Omit common suffixes like '_Islands' and '_City', unless that - would lead to ambiguity. E.g. prefer 'Cayman' to - 'Cayman_Islands' and 'Guatemala' to 'Guatemala_City', - but prefer 'Mexico_City' to 'Mexico' because the country - of Mexico has several time zones. - Use '_' to represent a space. - Omit '.' from abbreviations in names, e.g. prefer 'St_Helena' - to 'St._Helena'. - Do not change established names if they only marginally - violate the above rules. For example, don't change - the existing name 'Rome' to 'Milan' merely because - Milan's population has grown to be somewhat greater - than Rome's. - If a name is changed, put its old spelling in the 'backward' file. - This means old spellings will continue to work. - -The file 'zone1970.tab' lists geographical locations used to name time -zone rules. It is intended to be an exhaustive list of names for -geographic regions as described above; this is a subset of the names -in the data. Although a 'zone1970.tab' location's longitude -corresponds to its LMT offset with one hour for every 15 degrees east -longitude, this relationship is not exact. - -Older versions of this package used a different naming scheme, -and these older names are still supported. -See the file 'backward' for most of these older names -(e.g., 'US/Eastern' instead of 'America/New_York'). -The other old-fashioned names still supported are -'WET', 'CET', 'MET', and 'EET' (see the file 'europe'). - -Older versions of this package defined legacy names that are -incompatible with the first rule of location names, but which are -still supported. These legacy names are mostly defined in the file -'etcetera'. Also, the file 'backward' defines the legacy names -'GMT0', 'GMT-0', 'GMT+0' and 'Canada/East-Saskatchewan', and the file -'northamerica' defines the legacy names 'EST5EDT', 'CST6CDT', -'MST7MDT', and 'PST8PDT'. - -Excluding 'backward' should not affect the other data. If -'backward' is excluded, excluding 'etcetera' should not affect the -remaining data. - - ------ Time zone abbreviations ----- - -When this package is installed, it generates time zone abbreviations -like 'EST' to be compatible with human tradition and POSIX. -Here are the general rules used for choosing time zone abbreviations, -in decreasing order of importance: - - Use three or more characters that are ASCII alphanumerics or '+' or '-'. - Previous editions of this database also used characters like - ' ' and '?', but these characters have a special meaning to - the shell and cause commands like - set `date` - to have unexpected effects. - Previous editions of this rule required upper-case letters, - but the Congressman who introduced Chamorro Standard Time - preferred "ChST", so lower-case letters are now allowed. - Also, POSIX from 2001 on relaxed the rule to allow '-', '+', - and alphanumeric characters from the portable character set - in the current locale. In practice ASCII alphanumerics and - '+' and '-' are safe in all locales. - - In other words, in the C locale the POSIX extended regular - expression [-+[:alnum:]]{3,} should match the abbreviation. - This guarantees that all abbreviations could have been - specified by a POSIX TZ string. - - Use abbreviations that are in common use among English-speakers, - e.g. 'EST' for Eastern Standard Time in North America. - We assume that applications translate them to other languages - as part of the normal localization process; for example, - a French application might translate 'EST' to 'HNE'. - - For zones whose times are taken from a city's longitude, use the - traditional xMT notation, e.g. 'PMT' for Paris Mean Time. - The only name like this in current use is 'GMT'. - - Use 'LMT' for local mean time of locations before the introduction - of standard time; see "Scope of the tz database". - - If there is no common English abbreviation, use numeric offsets like - -05 and +0830 that are generated by zic's %z notation. - - Use current abbreviations for older timestamps to avoid confusion. - For example, in 1910 a common English abbreviation for UT +01 - in central Europe was 'MEZ' (short for both "Middle European - Zone" and for "Mitteleuropäische Zeit" in German). Nowadays - 'CET' ("Central European Time") is more common in English, and - the database uses 'CET' even for circa-1910 timestamps as this - is less confusing for modern users and avoids the need for - determining when 'CET' supplanted 'MEZ' in common usage. - - Use a consistent style in a zone's history. For example, if a zone's - history tends to use numeric abbreviations and a particular - entry could go either way, use a numeric abbreviation. - - [The remaining guidelines predate the introduction of %z. - They are problematic as they mean tz data entries invent - notation rather than record it. These guidelines are now - deprecated and the plan is to gradually move to %z for - inhabited locations and to "-00" for uninhabited locations.] - - If there is no common English abbreviation, abbreviate the English - translation of the usual phrase used by native speakers. - If this is not available or is a phrase mentioning the country - (e.g. "Cape Verde Time"), then: - - When a country is identified with a single or principal zone, - append 'T' to the country's ISO code, e.g. 'CVT' for - Cape Verde Time. For summer time append 'ST'; - for double summer time append 'DST'; etc. - Otherwise, take the first three letters of an English place - name identifying each zone and append 'T', 'ST', etc. - as before; e.g. 'CHAST' for CHAtham Summer Time. - - Use UT (with time zone abbreviation '-00') for locations while - uninhabited. The leading '-' is a flag that the time - zone is in some sense undefined; this notation is - derived from Internet RFC 3339. - -Application writers should note that these abbreviations are ambiguous -in practice: e.g. 'CST' has a different meaning in China than -it does in the United States. In new applications, it's often better -to use numeric UT offsets like '-0600' instead of time zone -abbreviations like 'CST'; this avoids the ambiguity. - - ------ Accuracy of the tz database ----- - -The tz database is not authoritative, and it surely has errors. -Corrections are welcome and encouraged; see the file CONTRIBUTING. -Users requiring authoritative data should consult national standards -bodies and the references cited in the database's comments. - -Errors in the tz database arise from many sources: - - * The tz database predicts future time stamps, and current predictions - will be incorrect after future governments change the rules. - For example, if today someone schedules a meeting for 13:00 next - October 1, Casablanca time, and tomorrow Morocco changes its - daylight saving rules, software can mess up after the rule change - if it blithely relies on conversions made before the change. - - * The pre-1970 entries in this database cover only a tiny sliver of how - clocks actually behaved; the vast majority of the necessary - information was lost or never recorded. Thousands more zones would - be needed if the tz database's scope were extended to cover even - just the known or guessed history of standard time; for example, - the current single entry for France would need to split into dozens - of entries, perhaps hundreds. And in most of the world even this - approach would be misleading due to widespread disagreement or - indifference about what times should be observed. In her 2015 book - "The Global Transformation of Time, 1870-1950", Vanessa Ogle writes - "Outside of Europe and North America there was no system of time - zones at all, often not even a stable landscape of mean times, - prior to the middle decades of the twentieth century". See: - Timothy Shenk, Booked: A Global History of Time. Dissent 2015-12-17 - https://www.dissentmagazine.org/blog/booked-a-global-history-of-time-vanessa-ogle - - * Most of the pre-1970 data entries come from unreliable sources, often - astrology books that lack citations and whose compilers evidently - invented entries when the true facts were unknown, without - reporting which entries were known and which were invented. - These books often contradict each other or give implausible entries, - and on the rare occasions when they are checked they are - typically found to be incorrect. - - * For the UK the tz database relies on years of first-class work done by - Joseph Myers and others; see . - Other countries are not done nearly as well. - - * Sometimes, different people in the same city would maintain clocks - that differed significantly. Railway time was used by railroad - companies (which did not always agree with each other), - church-clock time was used for birth certificates, etc. - Often this was merely common practice, but sometimes it was set by law. - For example, from 1891 to 1911 the UT offset in France was legally - 0:09:21 outside train stations and 0:04:21 inside. - - * Although a named location in the tz database stands for the - containing region, its pre-1970 data entries are often accurate for - only a small subset of that region. For example, Europe/London - stands for the United Kingdom, but its pre-1847 times are valid - only for locations that have London's exact meridian, and its 1847 - transition to GMT is known to be valid only for the L&NW and the - Caledonian railways. - - * The tz database does not record the earliest time for which a zone's - data entries are thereafter valid for every location in the region. - For example, Europe/London is valid for all locations in its - region after GMT was made the standard time, but the date of - standardization (1880-08-02) is not in the tz database, other than - in commentary. For many zones the earliest time of validity is - unknown. - - * The tz database does not record a region's boundaries, and in many - cases the boundaries are not known. For example, the zone - America/Kentucky/Louisville represents a region around the city of - Louisville, the boundaries of which are unclear. - - * Changes that are modeled as instantaneous transitions in the tz - database were often spread out over hours, days, or even decades. - - * Even if the time is specified by law, locations sometimes - deliberately flout the law. - - * Early timekeeping practices, even assuming perfect clocks, were - often not specified to the accuracy that the tz database requires. - - * Sometimes historical timekeeping was specified more precisely - than what the tz database can handle. For example, from 1909 to - 1937 Netherlands clocks were legally UT +00:19:32.13, but the tz - database cannot represent the fractional second. - - * Even when all the timestamp transitions recorded by the tz database - are correct, the tz rules that generate them may not faithfully - reflect the historical rules. For example, from 1922 until World - War II the UK moved clocks forward the day following the third - Saturday in April unless that was Easter, in which case it moved - clocks forward the previous Sunday. Because the tz database has no - way to specify Easter, these exceptional years are entered as - separate tz Rule lines, even though the legal rules did not change. - - * The tz database models pre-standard time using the proleptic Gregorian - calendar and local mean time (LMT), but many people used other - calendars and other timescales. For example, the Roman Empire used - the Julian calendar, and had 12 varying-length daytime hours with a - non-hour-based system at night. - - * Early clocks were less reliable, and data entries do not represent - clock error. - - * The tz database assumes Universal Time (UT) as an origin, even - though UT is not standardized for older time stamps. In the tz - database commentary, UT denotes a family of time standards that - includes Coordinated Universal Time (UTC) along with other variants - such as UT1 and GMT, with days starting at midnight. Although UT - equals UTC for modern time stamps, UTC was not defined until 1960, - so commentary uses the more-general abbreviation UT for time stamps - that might predate 1960. Since UT, UT1, etc. disagree slightly, - and since pre-1972 UTC seconds varied in length, interpretation of - older time stamps can be problematic when subsecond accuracy is - needed. - - * Civil time was not based on atomic time before 1972, and we don't - know the history of earth's rotation accurately enough to map SI - seconds to historical solar time to more than about one-hour - accuracy. See: Stephenson FR, Morrison LV, Hohenkerk CY. - Measurement of the Earth's rotation: 720 BC to AD 2015. - Proc Royal Soc A. 2016 Dec 7;472:20160404. - http://dx.doi.org/10.1098/rspa.2016.0404 - Also see: Espenak F. Uncertainty in Delta T (ΔT). - http://eclipse.gsfc.nasa.gov/SEhelp/uncertainty2004.html - - * The relationship between POSIX time (that is, UTC but ignoring leap - seconds) and UTC is not agreed upon after 1972. Although the POSIX - clock officially stops during an inserted leap second, at least one - proposed standard has it jumping back a second instead; and in - practice POSIX clocks more typically either progress glacially during - a leap second, or are slightly slowed while near a leap second. - - * The tz database does not represent how uncertain its information is. - Ideally it would contain information about when data entries are - incomplete or dicey. Partial temporal knowledge is a field of - active research, though, and it's not clear how to apply it here. - -In short, many, perhaps most, of the tz database's pre-1970 and future -time stamps are either wrong or misleading. Any attempt to pass the -tz database off as the definition of time should be unacceptable to -anybody who cares about the facts. In particular, the tz database's -LMT offsets should not be considered meaningful, and should not prompt -creation of zones merely because two locations differ in LMT or -transitioned to standard time at different dates. - - ------ Time and date functions ----- - -The tz code contains time and date functions that are upwards -compatible with those of POSIX. - -POSIX has the following properties and limitations. - -* In POSIX, time display in a process is controlled by the - environment variable TZ. Unfortunately, the POSIX TZ string takes - a form that is hard to describe and is error-prone in practice. - Also, POSIX TZ strings can't deal with other (for example, Israeli) - daylight saving time rules, or situations where more than two - time zone abbreviations are used in an area. - - The POSIX TZ string takes the following form: - - stdoffset[dst[offset][,date[/time],date[/time]]] - - where: - - std and dst - are 3 or more characters specifying the standard - and daylight saving time (DST) zone names. - Starting with POSIX.1-2001, std and dst may also be - in a quoted form like ""; this allows - "+" and "-" in the names. - offset - is of the form '[+-]hh:[mm[:ss]]' and specifies the - offset west of UT. 'hh' may be a single digit; 0<=hh<=24. - The default DST offset is one hour ahead of standard time. - date[/time],date[/time] - specifies the beginning and end of DST. If this is absent, - the system supplies its own rules for DST, and these can - differ from year to year; typically US DST rules are used. - time - takes the form 'hh:[mm[:ss]]' and defaults to 02:00. - This is the same format as the offset, except that a - leading '+' or '-' is not allowed. - date - takes one of the following forms: - Jn (1<=n<=365) - origin-1 day number not counting February 29 - n (0<=n<=365) - origin-0 day number counting February 29 if present - Mm.n.d (0[Sunday]<=d<=6[Saturday], 1<=n<=5, 1<=m<=12) - for the dth day of week n of month m of the year, - where week 1 is the first week in which day d appears, - and '5' stands for the last week in which day d appears - (which may be either the 4th or 5th week). - Typically, this is the only useful form; - the n and Jn forms are rarely used. - - Here is an example POSIX TZ string, for US Pacific time using rules - appropriate from 1987 through 2006: - - TZ='PST8PDT,M4.1.0/02:00,M10.5.0/02:00' - - This POSIX TZ string is hard to remember, and mishandles time stamps - before 1987 and after 2006. With this package you can use this - instead: - - TZ='America/Los_Angeles' - -* POSIX does not define the exact meaning of TZ values like "EST5EDT". - Typically the current US DST rules are used to interpret such values, - but this means that the US DST rules are compiled into each program - that does time conversion. This means that when US time conversion - rules change (as in the United States in 1987), all programs that - do time conversion must be recompiled to ensure proper results. - -* The TZ environment variable is process-global, which makes it hard - to write efficient, thread-safe applications that need access - to multiple time zones. - -* In POSIX, there's no tamper-proof way for a process to learn the - system's best idea of local wall clock. (This is important for - applications that an administrator wants used only at certain times - - without regard to whether the user has fiddled the "TZ" environment - variable. While an administrator can "do everything in UTC" to get - around the problem, doing so is inconvenient and precludes handling - daylight saving time shifts - as might be required to limit phone - calls to off-peak hours.) - -* POSIX provides no convenient and efficient way to determine the UT - offset and time zone abbreviation of arbitrary time stamps, - particularly for time zone settings that do not fit into the - POSIX model. - -* POSIX requires that systems ignore leap seconds. - -* The tz code attempts to support all the time_t implementations - allowed by POSIX. The time_t type represents a nonnegative count of - seconds since 1970-01-01 00:00:00 UTC, ignoring leap seconds. - In practice, time_t is usually a signed 64- or 32-bit integer; 32-bit - signed time_t values stop working after 2038-01-19 03:14:07 UTC, so - new implementations these days typically use a signed 64-bit integer. - Unsigned 32-bit integers are used on one or two platforms, - and 36-bit and 40-bit integers are also used occasionally. - Although earlier POSIX versions allowed time_t to be a - floating-point type, this was not supported by any practical - systems, and POSIX.1-2013 and the tz code both require time_t - to be an integer type. - -These are the extensions that have been made to the POSIX functions: - -* The "TZ" environment variable is used in generating the name of a file - from which time zone information is read (or is interpreted a la - POSIX); "TZ" is no longer constrained to be a three-letter time zone - name followed by a number of hours and an optional three-letter - daylight time zone name. The daylight saving time rules to be used - for a particular time zone are encoded in the time zone file; - the format of the file allows U.S., Australian, and other rules to be - encoded, and allows for situations where more than two time zone - abbreviations are used. - - It was recognized that allowing the "TZ" environment variable to - take on values such as "America/New_York" might cause "old" programs - (that expect "TZ" to have a certain form) to operate incorrectly; - consideration was given to using some other environment variable - (for example, "TIMEZONE") to hold the string used to generate the - time zone information file name. In the end, however, it was decided - to continue using "TZ": it is widely used for time zone purposes; - separately maintaining both "TZ" and "TIMEZONE" seemed a nuisance; - and systems where "new" forms of "TZ" might cause problems can simply - use TZ values such as "EST5EDT" which can be used both by - "new" programs (a la POSIX) and "old" programs (as zone names and - offsets). - -* The code supports platforms with a UT offset member in struct tm, - e.g., tm_gmtoff. - -* The code supports platforms with a time zone abbreviation member in - struct tm, e.g., tm_zone. - -* Since the "TZ" environment variable can now be used to control time - conversion, the "daylight" and "timezone" variables are no longer - needed. (These variables are defined and set by "tzset"; however, their - values will not be used by "localtime.") - -* Functions tzalloc, tzfree, localtime_rz, and mktime_z for - more-efficient thread-safe applications that need to use - multiple time zones. The tzalloc and tzfree functions - allocate and free objects of type timezone_t, and localtime_rz - and mktime_z are like localtime_r and mktime with an extra - timezone_t argument. The functions were inspired by NetBSD. - -* A function "tzsetwall" has been added to arrange for the system's - best approximation to local wall clock time to be delivered by - subsequent calls to "localtime." Source code for portable - applications that "must" run on local wall clock time should call - "tzsetwall();" if such code is moved to "old" systems that don't - provide tzsetwall, you won't be able to generate an executable program. - (These time zone functions also arrange for local wall clock time to be - used if tzset is called - directly or indirectly - and there's no "TZ" - environment variable; portable applications should not, however, rely - on this behavior since it's not the way SVR2 systems behave.) - -* Negative time_t values are supported, on systems where time_t is signed. - -* These functions can account for leap seconds, thanks to Bradley White. - -Points of interest to folks with other systems: - -* Code compatible with this package is already part of many platforms, - including GNU/Linux, Android, the BSDs, Chromium OS, Cygwin, AIX, iOS, - BlackBery 10, macOS, Microsoft Windows, OpenVMS, and Solaris. - On such hosts, the primary use of this package - is to update obsolete time zone rule tables. - To do this, you may need to compile the time zone compiler - 'zic' supplied with this package instead of using the system 'zic', - since the format of zic's input is occasionally extended, - and a platform may still be shipping an older zic. - -* The UNIX Version 7 "timezone" function is not present in this package; - it's impossible to reliably map timezone's arguments (a "minutes west - of GMT" value and a "daylight saving time in effect" flag) to a - time zone abbreviation, and we refuse to guess. - Programs that in the past used the timezone function may now examine - tzname[localtime(&clock)->tm_isdst] to learn the correct time - zone abbreviation to use. Alternatively, use - localtime(&clock)->tm_zone if this has been enabled. - -* The 4.2BSD gettimeofday function is not used in this package. - This formerly let users obtain the current UTC offset and DST flag, - but this functionality was removed in later versions of BSD. - -* In SVR2, time conversion fails for near-minimum or near-maximum - time_t values when doing conversions for places that don't use UT. - This package takes care to do these conversions correctly. - A comment in the source code tells how to get compatibly wrong - results. - -The functions that are conditionally compiled if STD_INSPIRED is defined -should, at this point, be looked on primarily as food for thought. They are -not in any sense "standard compatible" - some are not, in fact, specified in -*any* standard. They do, however, represent responses of various authors to -standardization proposals. - -Other time conversion proposals, in particular the one developed by folks at -Hewlett Packard, offer a wider selection of functions that provide capabilities -beyond those provided here. The absence of such functions from this package -is not meant to discourage the development, standardization, or use of such -functions. Rather, their absence reflects the decision to make this package -contain valid extensions to POSIX, to ensure its broad acceptability. If -more powerful time conversion functions can be standardized, so much the -better. - - ------ Interface stability ----- - -The tz code and data supply the following interfaces: - - * A set of zone names as per "Names of time zone rules" above. - - * Library functions described in "Time and date functions" above. - - * The programs tzselect, zdump, and zic, documented in their man pages. - - * The format of zic input files, documented in the zic man page. - - * The format of zic output files, documented in the tzfile man page. - - * The format of zone table files, documented in zone1970.tab. - - * The format of the country code file, documented in iso3166.tab. - - * The version number of the code and data, as the first line of - the text file 'version' in each release. - -Interface changes in a release attempt to preserve compatibility with -recent releases. For example, tz data files typically do not rely on -recently-added zic features, so that users can run older zic versions -to process newer data files. The tz-link.htm file describes how -releases are tagged and distributed. - -Interfaces not listed above are less stable. For example, users -should not rely on particular UT offsets or abbreviations for time -stamps, as data entries are often based on guesswork and these guesses -may be corrected or improved. - - ------ Calendrical issues ----- - -Calendrical issues are a bit out of scope for a time zone database, -but they indicate the sort of problems that we would run into if we -extended the time zone database further into the past. An excellent -resource in this area is Nachum Dershowitz and Edward M. Reingold, -Calendrical Calculations: Third Edition, Cambridge University Press (2008) -. -Other information and sources are given below. They sometimes disagree. - - -France - -Gregorian calendar adopted 1582-12-20. -French Revolutionary calendar used 1793-11-24 through 1805-12-31, -and (in Paris only) 1871-05-06 through 1871-05-23. - - -Russia - -From Chris Carrier (1996-12-02): -On 1929-10-01 the Soviet Union instituted an "Eternal Calendar" -with 30-day months plus 5 holidays, with a 5-day week. -On 1931-12-01 it changed to a 6-day week; in 1934 it reverted to the -Gregorian calendar while retaining the 6-day week; on 1940-06-27 it -reverted to the 7-day week. With the 6-day week the usual days -off were the 6th, 12th, 18th, 24th and 30th of the month. -(Source: Evitiar Zerubavel, _The Seven Day Circle_) - - -Mark Brader reported a similar story in "The Book of Calendars", edited -by Frank Parise (1982, Facts on File, ISBN 0-8719-6467-8), page 377. But: - -From: Petteri Sulonen (via Usenet) -Date: 14 Jan 1999 00:00:00 GMT -... - -If your source is correct, how come documents between 1929 and 1940 were -still dated using the conventional, Gregorian calendar? - -I can post a scan of a document dated December 1, 1934, signed by -Yenukidze, the secretary, on behalf of Kalinin, the President of the -Executive Committee of the Supreme Soviet, if you like. - - - -Sweden (and Finland) - -From: Mark Brader -Subject: Re: Gregorian reform - a part of locale? - -Date: 1996-07-06 - -In 1700, Denmark made the transition from Julian to Gregorian. Sweden -decided to *start* a transition in 1700 as well, but rather than have one of -those unsightly calendar gaps :-), they simply decreed that the next leap -year after 1696 would be in 1744 - putting the whole country on a calendar -different from both Julian and Gregorian for a period of 40 years. - -However, in 1704 something went wrong and the plan was not carried through; -they did, after all, have a leap year that year. And one in 1708. In 1712 -they gave it up and went back to Julian, putting 30 days in February that -year!... - -Then in 1753, Sweden made the transition to Gregorian in the usual manner, -getting there only 13 years behind the original schedule. - -(A previous posting of this story was challenged, and Swedish readers -produced the following references to support it: "Tideräkning och historia" -by Natanael Beckman (1924) and "Tid, en bok om tideräkning och -kalenderväsen" by Lars-Olof Lodén (1968). - - -Grotefend's data - -From: "Michael Palmer" [with one obvious typo fixed] -Subject: Re: Gregorian Calendar (was Re: Another FHC related question -Newsgroups: soc.genealogy.german -Date: Tue, 9 Feb 1999 02:32:48 -800 -... - -The following is a(n incomplete) listing, arranged chronologically, of -European states, with the date they converted from the Julian to the -Gregorian calendar: - -04/15 Oct 1582 - Italy (with exceptions), Spain, Portugal, Poland (Roman - Catholics and Danzig only) -09/20 Dec 1582 - France, Lorraine - -21 Dec 1582/ - 01 Jan 1583 - Holland, Brabant, Flanders, Hennegau -10/21 Feb 1583 - bishopric of Liege (Lüttich) -13/24 Feb 1583 - bishopric of Augsburg -04/15 Oct 1583 - electorate of Trier -05/16 Oct 1583 - Bavaria, bishoprics of Freising, Eichstedt, Regensburg, - Salzburg, Brixen -13/24 Oct 1583 - Austrian Oberelsaß and Breisgau -20/31 Oct 1583 - bishopric of Basel -02/13 Nov 1583 - duchy of Jülich-Berg -02/13 Nov 1583 - electorate and city of Köln -04/15 Nov 1583 - bishopric of Würzburg -11/22 Nov 1583 - electorate of Mainz -16/27 Nov 1583 - bishopric of Strassburg and the margraviate of Baden -17/28 Nov 1583 - bishopric of Münster and duchy of Cleve -14/25 Dec 1583 - Steiermark - -06/17 Jan 1584 - Austria and Bohemia -11/22 Jan 1584 - Lucerne, Uri, Schwyz, Zug, Freiburg, Solothurn -12/23 Jan 1584 - Silesia and the Lausitz -22 Jan/ - 02 Feb 1584 - Hungary (legally on 21 Oct 1587) - Jun 1584 - Unterwalden -01/12 Jul 1584 - duchy of Westfalen - -16/27 Jun 1585 - bishopric of Paderborn - -14/25 Dec 1590 - Transylvania - -22 Aug/ - 02 Sep 1612 - duchy of Prussia - -13/24 Dec 1614 - Pfalz-Neuburg - - 1617 - duchy of Kurland (reverted to the Julian calendar in - 1796) - - 1624 - bishopric of Osnabrück - - 1630 - bishopric of Minden - -15/26 Mar 1631 - bishopric of Hildesheim - - 1655 - Kanton Wallis - -05/16 Feb 1682 - city of Strassburg - -18 Feb/ - 01 Mar 1700 - Protestant Germany (including Swedish possessions in - Germany), Denmark, Norway -30 Jun/ - 12 Jul 1700 - Gelderland, Zutphen -10 Nov/ - 12 Dec 1700 - Utrecht, Overijssel - -31 Dec 1700/ - 12 Jan 1701 - Friesland, Groningen, Zürich, Bern, Basel, Geneva, - Turgau, and Schaffhausen - - 1724 - Glarus, Appenzell, and the city of St. Gallen - -01 Jan 1750 - Pisa and Florence - -02/14 Sep 1752 - Great Britain - -17 Feb/ - 01 Mar 1753 - Sweden - -1760-1812 - Graubünden - -The Russian empire (including Finland and the Baltic states) did not -convert to the Gregorian calendar until the Soviet revolution of 1917. - -Source: H. Grotefend, _Taschenbuch der Zeitrechnung des deutschen -Mittelalters und der Neuzeit_, herausgegeben von Dr. O. Grotefend -(Hannover: Hahnsche Buchhandlung, 1941), pp. 26-28. - - ------ Time and time zones on Mars ----- - -Some people's work schedules use Mars time. Jet Propulsion Laboratory -(JPL) coordinators have kept Mars time on and off at least since 1997 -for the Mars Pathfinder mission. Some of their family members have -also adapted to Mars time. Dozens of special Mars watches were built -for JPL workers who kept Mars time during the Mars Exploration -Rovers mission (2004). These timepieces look like normal Seikos and -Citizens but use Mars seconds rather than terrestrial seconds. - -A Mars solar day is called a "sol" and has a mean period equal to -about 24 hours 39 minutes 35.244 seconds in terrestrial time. It is -divided into a conventional 24-hour clock, so each Mars second equals -about 1.02749125 terrestrial seconds. - -The prime meridian of Mars goes through the center of the crater -Airy-0, named in honor of the British astronomer who built the -Greenwich telescope that defines Earth's prime meridian. Mean solar -time on the Mars prime meridian is called Mars Coordinated Time (MTC). - -Each landed mission on Mars has adopted a different reference for -solar time keeping, so there is no real standard for Mars time zones. -For example, the Mars Exploration Rover project (2004) defined two -time zones "Local Solar Time A" and "Local Solar Time B" for its two -missions, each zone designed so that its time equals local true solar -time at approximately the middle of the nominal mission. Such a "time -zone" is not particularly suited for any application other than the -mission itself. - -Many calendars have been proposed for Mars, but none have achieved -wide acceptance. Astronomers often use Mars Sol Date (MSD) which is a -sequential count of Mars solar days elapsed since about 1873-12-29 -12:00 GMT. - -The tz database does not currently support Mars time, but it is -documented here in the hopes that support will be added eventually. - -Sources: - -Michael Allison and Robert Schmunk, -"Technical Notes on Mars Solar Time as Adopted by the Mars24 Sunclock" - (2012-08-08). - -Jia-Rui Chong, "Workdays Fit for a Martian", Los Angeles Times - -(2004-01-14), pp A1, A20-A21. - -Tom Chmielewski, "Jet Lag Is Worse on Mars", The Atlantic (2015-02-26) - - ------ - -This file is in the public domain, so clarified as of 2009-05-17 by -Arthur David Olson. - ------ -Local Variables: -coding: utf-8 -End: