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ICU-2235 improve description of .cnv conversion table data format

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X-SVN-Rev: 13154
This commit is contained in:
Markus Scherer 2003-09-22 13:53:51 +00:00
parent 969599a083
commit 22ab8d901a
1 changed files with 78 additions and 26 deletions
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104
icu4c/source/common/ucnvmbcs.h
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@ -21,6 +21,83 @@
#include "unicode/ucnv.h"
#include "ucnv_bld.h"
/**
* ICU conversion (.cnv) data file structure, following the usual UDataInfo
* header.
*
* Format version: 6.2
*
* struct UConverterStaticData -- struct containing the converter name, IBM CCSID,
* min/max bytes per character, etc.
* see ucnv_bld.h
*
* --------------------
*
* The static data is followed by conversionType-specific data structures.
* At the moment, there are only variations of MBCS converters. They all have
* the same toUnicode structures, while the fromUnicode structures for SBCS
* differ from those for other MBCS-style converters.
*
* MBCS-style data structure following the static data.
* Offsets are counted in bytes from the beginning of the MBCS header structure.
* Details about usage in comments in ucnvmbcs.c.
*
* struct _MBCSHeader (see the definition in this header file below)
* contains 32-bit fields as follows:
* 8 values:
* 0 uint8_t[4] MBCS version in UVersionInfo format (currently 4.1.0.0)
* 1 uint32_t countStates
* 2 uint32_t countToUFallbacks
* 3 uint32_t offsetToUCodeUnits
* 4 uint32_t offsetFromUTable
* 5 uint32_t offsetFromUBytes
* 6 uint32_t flags, bits:
* 31.. 8 reserved
* 7.. 0 outputType
* 7 uint32_t fromUBytesLength -- _MBCSHeader.version 4.1 (ICU 2.4) and higher
* counts bytes in fromUBytes[]
*
* int32_t stateTable[countStates][256];
*
* struct _MBCSToUFallback { (fallbacks are sorted by offset)
* uint32_t offset;
* UChar32 codePoint;
* } toUFallbacks[countToUFallbacks];
*
* uint16_t unicodeCodeUnits[(offsetFromUTable-offsetToUCodeUnits)/2];
* (padded to an even number of units)
*
* -- stage 1 tables
* if(staticData.unicodeMask&UCNV_HAS_SUPPLEMENTARY) {
* -- stage 1 table for all of Unicode
* uint16_t fromUTable[0x440]; (32-bit-aligned)
* } else {
* -- BMP-only tables have a smaller stage 1 table
* uint16_t fromUTable[0x40]; (32-bit-aligned)
* }
*
* -- stage 2 tables
* length determined by top of stage 1 and bottom of stage 3 tables
* if(outputType==MBCS_OUTPUT_1) {
* -- SBCS: pure indexes
* uint16_t stage 2 indexes[?];
* } else {
* -- DBCS, MBCS, EBCDIC_STATEFUL, ...: roundtrip flags and indexes
* uint32_t stage 2 flags and indexes[?];
* }
*
* -- stage 3 tables with byte results
* if(outputType==MBCS_OUTPUT_1) {
* -- SBCS: each 16-bit result contains flags and the result byte, see ucnvmbcs.c
* uint16_t fromUBytes[fromUBytesLength/2];
* } else {
* -- DBCS, MBCS, EBCDIC_STATEFUL, ... 2/3/4 bytes result, see ucnvmbcs.c
* uint8_t fromUBytes[fromUBytesLength]; or
* uint16_t fromUBytes[fromUBytesLength/2]; or
* uint32_t fromUBytes[fromUBytesLength/4];
* }
*/
/* MBCS converter data and state -------------------------------------------- */
/**
@ -136,32 +213,7 @@ typedef struct UConverterMBCSTable {
} UConverterMBCSTable;
/**
* MBCS data structure as part of a .cnv file:
*
* uint32_t [8]; -- 8 values:
* 0 MBCS version in UVersionInfo format (1.0.0.0)
* 1 countStates
* 2 countToUFallbacks
* 3 offsetToUCodeUnits (offsets are counted from the beginning of this header structure)
* 4 offsetFromUTable
* 5 offsetFromUBytes
* 6 flags, bits:
* 31.. 8 reserved
* 7.. 0 outputType
* 7 fromUBytesLength -- header.version 4.1 (ICU 2.4) and higher
*
* stateTable[countStates][256];
*
* struct { (fallbacks are sorted by offset)
* uint32_t offset;
* UChar32 codePoint;
* } toUFallbacks[countToUFallbacks];
*
* uint16_t unicodeCodeUnits[?]; (even number of units or padded)
*
* uint16_t fromUTable[0x440+?]; (32-bit-aligned)
*
* uint8_t fromUBytes[?];
* MBCS data header. See data format description above.
*/
typedef struct {
UVersionInfo version;