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| author | darylm503 <darylm503@6f19259b-4bc3-4df7-8a09-765794883524> | 2011-04-27 21:42:16 +0000 |
|---|---|---|
| committer | darylm503 <darylm503@6f19259b-4bc3-4df7-8a09-765794883524> | 2011-04-27 21:42:16 +0000 |
| commit | 2aa62f2bc9a9654687b377d9ca8a8c2c860a3852 (patch) | |
| tree | 62a0991a44327154fb88bf95bd6f7522053db7bb /StdLib/LibC/Time/Theory.txt | |
| parent | 98790d814871cc30bbd536673d3a0948047cd2f0 (diff) | |
| download | edk2-platforms-2aa62f2bc9a9654687b377d9ca8a8c2c860a3852.tar.xz | |
Standard Libraries for EDK II.
This set of three packages: AppPkg, StdLib, StdLibPrivateInternalFiles; contains the implementation of libraries based upon non-UEFI standards such as ISO/IEC-9899, the library portion of the C Language Standard, POSIX, etc.
AppPkg contains applications that make use of the standard libraries defined in the StdLib Package.
StdLib contains header (include) files and the implementations of the standard libraries.
StdLibPrivateInternalFiles contains files for the exclusive use of the library implementations in StdLib. These files should never be directly referenced from applications or other code.
git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@11600 6f19259b-4bc3-4df7-8a09-765794883524
Diffstat (limited to 'StdLib/LibC/Time/Theory.txt')
| -rw-r--r-- | StdLib/LibC/Time/Theory.txt | 553 |
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diff --git a/StdLib/LibC/Time/Theory.txt b/StdLib/LibC/Time/Theory.txt new file mode 100644 index 0000000000..f8e77adbdf --- /dev/null +++ b/StdLib/LibC/Time/Theory.txt @@ -0,0 +1,553 @@ +# $NetBSD: Theory,v 1.8 2004/05/27 20:39:49 kleink Exp $
+@(#)Theory 7.15
+
+
+----- Outline -----
+
+ Time and date functions
+ Names of time zone regions
+ Time zone abbreviations
+ Calendrical issues
+ Time and time zones on Mars
+
+
+----- Time and date functions -----
+
+These time and date functions are upwards compatible with POSIX.1,
+an international standard for UNIX-like systems.
+As of this writing, the current edition of POSIX.1 is:
+
+ Information technology --Portable Operating System Interface (POSIX (R))
+ -- Part 1: System Application Program Interface (API) [C Language]
+ ISO/IEC 9945-1:1996
+ ANSI/IEEE Std 1003.1, 1996 Edition
+ 1996-07-12
+
+POSIX.1 has the following properties and limitations.
+
+* In POSIX.1, time display in a process is controlled by the
+ environment variable TZ. Unfortunately, the POSIX.1 TZ string takes
+ a form that is hard to describe and is error-prone in practice.
+ Also, POSIX.1 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.1 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.
+ offset
+ is of the form `[-]hh:[mm[:ss]]' and specifies the
+ offset west of UTC. 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.
+ 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).
+
+* In POSIX.1, when a TZ value like "EST5EDT" is parsed,
+ typically the current US DST rules are used,
+ 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.
+
+* In POSIX.1, 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.1 requires that systems ignore leap seconds.
+
+These are the extensions that have been made to the POSIX.1 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).
+
+* To handle places where more than two time zone abbreviations are used,
+ the functions "localtime" and "gmtime" set tzname[tmp->tm_isdst]
+ (where "tmp" is the value the function returns) to the time zone
+ abbreviation to be used. This differs from POSIX.1, where the elements
+ of tzname are only changed as a result of calls to tzset.
+
+* 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.")
+
+* The "localtime" function has been set up to deliver correct results
+ for near-minimum or near-maximum time_t values. (A comment in the
+ source code tells how to get compatibly wrong results).
+
+* 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.)
+
+* These functions can account for leap seconds, thanks to Bradley White
+ (bww@k.cs.cmu.edu).
+
+Points of interest to folks with other systems:
+
+* This package is already part of many POSIX-compliant hosts,
+ including BSD, HP, Linux, Network Appliance, SCO, SGI, and Sun.
+ 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 changed slightly in late 1994,
+ and many vendors still do not support the new input format.
+
+* 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 UTC.
+ This package takes care to do these conversions correctly.
+
+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.1, to ensure its broad
+acceptability. If more powerful time conversion functions can be standardized,
+so much the better.
+
+
+----- Names of time zone rule files -----
+
+The time zone rule file naming conventions attempt to strike a balance
+among the following goals:
+
+ * Uniquely identify every national region where clocks have all
+ agreed since 1970. This is essential for the intended use: static
+ clocks keeping local civil time.
+
+ * Indicate to humans as to where that region is. This simplifes use.
+
+ * Be robust in the presence of political changes. This reduces the
+ number of updates and backward-compatibility hacks. 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.
+ This promotes use of the technology.
+
+ * Use a consistent naming convention over the entire world.
+ This simplifies both use and maintenance.
+
+This naming convention is not intended for use by inexperienced users
+to select TZ values by themselves (though they can of course examine
+and reuse existing settings). Distributors should provide
+documentation and/or a simple selection interface that explains the
+names; see the 'tzselect' program supplied with this distribution for
+one example.
+
+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 `/'). 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'.
+ Include at least one location per time zone rule set per country.
+ One such location is enough. Use ISO 3166 (see the file
+ iso3166.tab) to help decide whether something is a country.
+ If all the clocks in a country's 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 Jose 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 true name (which uses Greek letters).
+ The POSIX file name restrictions encourage this rule.
+ Use the most populous among locations in a country's time 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.
+
+The file `zone.tab' lists the geographical locations used to name
+time zone rule files.
+
+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', `EET' (see the file `europe'),
+and `Factory' (see the file `factory').
+
+
+----- Time zone abbreviations -----
+
+When this package is installed, it generates time zone abbreviations
+like `EST' to be compatible with human tradition and POSIX.1.
+Here are the general rules used for choosing time zone abbreviations,
+in decreasing order of importance:
+
+ Use abbreviations that consist of three or more ASCII letters.
+ 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 the rule has been relaxed.
+
+ This rule guarantees that all abbreviations could have
+ been specified by a POSIX.1 TZ string. POSIX.1
+ requires at least three characters for an
+ abbreviation. POSIX.1-1996 says that an abbreviation
+ cannot start with ':', and cannot contain ',', '-',
+ '+', NUL, or a digit. Draft 7 of POSIX 1003.1-200x
+ changes this rule to say that an abbreviation can
+ contain only '-', '+', and alphanumeric characters in
+ the current locale. To be portable to both sets of
+ rules, an abbreviation must therefore use only ASCII
+ letters, as these are the only letters that are
+ alphabetic in all locales.
+
+ 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'.
+
+ 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 has a single or principal time zone region,
+ 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.
+ When a country has multiple time zones, take the first three
+ letters of an English place name identifying each zone
+ and then append `T', `ST', etc. as before;
+ e.g. `VLAST' for VLAdivostok Summer Time.
+
+ Use "zzz" for locations while uninhabited. The mnemonic is that
+ these locations are, in some sense, asleep.
+
+Application writers should note that these abbreviations are ambiguous
+in practice: e.g. `EST' has a different meaning in Australia than
+it does in the United States. In new applications, it's often better
+to use numeric UTC offsets like `-0500' instead of time zone
+abbreviations like `EST'; this avoids the ambiguity.
+
+
+----- 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,
+<a href="http://emr.cs.uiuc.edu/home/reingold/calendar-book/index.shtml">
+Calendrical Calculations
+</a>, Cambridge University Press (1997). 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 <72157.3334@CompuServe.COM> (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
+Message-ID: <Petteri.Sulonen-1401991626030001@lapin-kulta.in.helsinki.fi>
+
+If your source is correct, how come documents between 1929 -- 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: msb@sq.com (Mark Brader)
+<a href="news:1996Jul6.012937.29190@sq.com">
+Subject: Re: Gregorian reform -- a part of locale?
+</a>
+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: "Tiderakning och historia"
+by Natanael Beckman (1924) and "Tid, en bok om tiderakning och
+kalendervasen" by Lars-Olof Lode'n (no date was given).)
+
+
+Grotefend's data
+
+From: "Michael Palmer" <mpalmer@netcom.com> [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
+Message-ID: <199902091032.CAA09644@netcom10.netcom.com>
+
+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 (L"uttich)
+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 J"ulich-Berg
+02/13 Nov 1583 - electorate and city of K"oln
+04/15 Nov 1583 - bishopric of W"urzburg
+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 M"unster and duchy of Cleve
+14/25 Dec 1583 - Steiermark
+
+06/17 Jan 1584 - Austria and Bohemia
+11/22 Jan 1584 - Luzern, 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 Osnabr"uck
+
+ 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, Z"urich, 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 - Graub"unden
+
+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 have adjusted their work schedules to fit Mars time.
+Dozens of special Mars watches were built for Jet Propulsion
+Laboratory 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"
+<http://www.giss.nasa.gov/tools/mars24/help/notes.html> (2004-03-15).
+
+Jia-Rui Chong, "Workdays Fit for a Martian", Los Angeles Times
+(2004-01-14), pp A1, A20-A21.
|