161 lines
6.3 KiB
C
161 lines
6.3 KiB
C
/*
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**********************************************************************
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* Copyright (C) 1999, International Business Machines
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* Corporation and others. All Rights Reserved.
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**********************************************************************
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* Date Name Description
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* 11/24/99 aliu Creation.
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* 12/13/1999 srl Padded OffsetIndex to 4 byte values
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**********************************************************************
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*/
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#ifndef TZDAT_H
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#define TZDAT_H
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#include "unicode/utypes.h"
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/* This file defines the format of the memory-mapped data file
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* containing system time zone data for icu. See also gentz
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* and tz.pl.
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*
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* The format is designed specifically to allow certain operations:
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*
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* 1. Performing a fast binary search by name, and locating the
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* corresponding zone data. This is the most important operation.
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* It corresponds to the TimeZone::createTimeZone() method.
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*
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* 2. Performing a fast iteration over zones having a specific GMT
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* offset. For this operation, the zone data need not be
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* retrieved, just the IDs. This corresponds to the
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* TimeZone::createAvailableIDs(int32_t) method.
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*
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* 3. Iterating over all zone IDs. This corresponds to the
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* TimeZone::createAvailableIDs() method.
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*
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* The createAvailableIDs() methods return arrays of pointers to
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* existing static UnicodeString IDs that it owns. Thus
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* createAvailableIDs() needs a way to reference one of these IDs when
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* iterating. Note that these IDs are _not_ stored in the
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* memory-mapped data file, so we cannot store offsets. To solve this
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* problem, we define a canonical index number for each zone. This
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* index number runs from 0..n-1, where n is the total number of
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* zones. The name table is stored in index number order, and we
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* provide a table that is sorted by GMT offset with keys being GMT
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* offset values and values being canonical index numbers.
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*
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* (Later, we might change createAvailableIDs() to return char*
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* strings rather than UnicodeString pointers. In that case, this
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* data structure could be modified to index into the name table
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* directly.)
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*
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* In the following table, sizes are estimated sizes for a zone list
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* of about 200 standard and 200 DST zones, which is typical in 1999.
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*
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* 0K TZHeader
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* 2K Standard zone table (StandardZone[])
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* 4K DST zone table (Zone[])
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* 2K Index table, sorted by name, 4 bytes / zone
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* This is a list of 'count' deltas sorted in ascending
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* lexicographic order of name string.
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* 1K Index table, sorted by gmtOffset then name. See
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* OffsetIndex struct.
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* 6K Name table - always last
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* This is all the zone names, in lexicographic order,
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* with zero bytes terminating each name.
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* 14K TOTAL
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*
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* Any field with a name ending in "delta" is an offset value
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* from the first byte of the TZHeader structure, unless otherwise
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* specified.
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*
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* When using the name index table and the offset index table,
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* code can determine whether an indexed zone is a standard
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* zone or a DST zone by examining its delta. If the delta is
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* less than dstDelta, it is a standard zone. Otherwise it
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* is a DST zone.
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*/
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struct TZHeader {
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uint16_t versionYear; // e.g. "1999j" -> 1999
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uint16_t versionSuffix; // e.g. "1999j" -> 10
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uint32_t count; // standardCount + dstCount
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uint32_t standardCount; // # of standard zones
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uint32_t dstCount; // # of dst zones
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uint32_t nameIndexDelta; // delta to name index table
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uint32_t offsetIndexDelta; // delta to gmtOffset index table
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uint32_t standardDelta; // delta to standard zones ALWAYS < dstDelta
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uint32_t dstDelta; // delta to dst zones ALWAYS > standardDelta
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uint32_t nameTableDelta; // delta to name (aka ID) table
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/* NOTE: Currently the standard and DST zone counts and deltas are
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* unused (all zones are referenced via the name index table).
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* However, they are retained for possible future use.
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*/
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};
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struct StandardZone {
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int32_t gmtOffset; // gmt offset in milliseconds
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};
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struct TZRule {
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uint8_t month; // month
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int8_t dowim; // dowim
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int8_t dow; // dow
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uint16_t time; // time in minutes
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int8_t mode; // (w/s/u) == TimeZone::TimeMode enum as int
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};
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struct DSTZone {
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int32_t gmtOffset; // gmtoffset in milliseconds
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uint16_t dstSavings; // savings in minutes
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TZRule onsetRule; // onset rule
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TZRule ceaseRule; // cease rule
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};
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/**
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* This variable-sized struct makes up the offset index table. To get
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* from one table entry to the next, add the nextEntryDelta. If the
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* nextEntryDelta is zero then this is the last entry. The offset
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* index table is designed for sequential access, not random access.
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* Given the small number of distinct offsets (39 in 1999j), this
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* suffices.
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*
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* The value of default is the zone within this list that should be
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* selected as the default zone in the absence of any other
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* discriminating information. This information comes from the file
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* tz.default. Note that this is itself a zone number, like
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* those in the array starting at &zoneNumber.
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*
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* The gmtOffset field must be 4-aligned for some architectures. To
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* ensure this, we do two things: 1. The entire struct is 4-aligned.
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* 2. The gmtOffset is placed at a 4-aligned position within the
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* struct. 3. The size of the whole structure is padded out to 4n
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* bytes. We achieve this last condition by adding two bytes of
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* padding after the last zoneNumber, if count is _even_. That is,
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* the struct size is 10+2count+padding, where padding is (count%2==0
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* ? 2:0). See gentz for implementation.
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*/
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struct OffsetIndex {
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int32_t gmtOffset; // in ms - 4-aligned
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uint16_t nextEntryDelta;
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uint16_t defaultZone; // a zone number from 0..TZHeader.count-1
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uint16_t count;
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uint16_t zoneNumber; // There are actually 'count' uint16_t's here
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// Following the 'count' uint16_t's starting with zoneNumber,
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// there may be two bytes of padding to make the whole struct have
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// a size of 4n. nextEntryDelta skips over any padding.
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};
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// Information used to identify and validate the data
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#define TZ_DATA_NAME "tz"
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#define TZ_DATA_TYPE "dat"
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// Fields in UDataInfo:
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static const char TZ_SIG[] = "zone"; // dataFormat
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static const int8_t TZ_FORMAT_VERSION = 2; // formatVersion[0]
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#endif
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