76 lines
2.7 KiB
Plaintext
76 lines
2.7 KiB
Plaintext
Readme file for ICU time zone data (source/tools/gentz)
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RAW DATA
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--------
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The time zone data in ICU is taken from the UNIX data files at
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ftp://elsie.nci.nih.gov/pub/tzdata<year>. The other input to the
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process is an alias table, described below.
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BUILD PROCESS
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-------------
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Two tools are used to process the data into a format suitable for ICU:
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tz.pl directory of raw data files + tz.alias -> tz.txt
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gentz tz.txt -> tz.dat (memory mappable binary file)
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After gentz is run, standard ICU data tools are used to incorporate
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tz.dat into the icudata module.
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In order to incorporate the raw data from that source into ICU, take
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the following steps.
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1. Download the archive of current zone data. This should be a file
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named something like tzdata1999j.tar.gz. Use the URL listed above.
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2. Unpack the archive into a directory, retaining the name of the
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archive. For example, unpack tzdata1999j.tar.gz into tzdata1999j/.
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Place this directory anywhere; one option is to place it within
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source/tools/gentz.
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3. Run the perl script tz.pl, passing it the directory location as a
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command-line argument. On Windows system use the batch file
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tz.bat. The output of this step is the intermediate text file
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source/tools/gentz/tz.txt.
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4. Run source/tools/makedata on Windows. On UNIX systems the
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equivalent build steps are performed by 'make' and 'make install'.
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The tz.txt file is typically checked into CVS, whereas the raw data
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files are not, since they are readily available from the URL listed
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above.
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ALIAS TABLE
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-----------
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For backward compatibility, we define several three-letter IDs that
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have been used since early ICU and correspond to IDs used in old JDKs.
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These IDs are listed in tz.alias. The tz.pl script processes this
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alias table and issues errors if there are problems.
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IDS
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---
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All *system* zone IDs must consist only of characters in the invariant
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set. See utypes.h for an explanation of what this means. If an ID is
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encountered that contains a non-invariant character, tz.pl complains.
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Non-system zones may try to use non-invariant characters, but they
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shouldn't because of possible collisions with system IDs when the
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invariant char converter is used (see TimeZone class for details).
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Etc/GMT...
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----------
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Users may be confused by the fact that various zones with names of the
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form Etc/GMT+n appear to have an offset of the wrong sign. For
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example, Etc/GMT+8 is 8 hours *behind* GMT; that is, it corresponds to
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what one typically sees displayed as "GMT-8:00". The reason for this
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inversion is explained in the UNIX zone data file "etcetera".
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Briefly, this is done intentionally in order to comply with
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POSIX-style signedness. In ICU we reproduce the UNIX zone behavior
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faithfully, including this confusing aspect.
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Alan Liu 1999
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