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