The deduplication table is a multi-level table of pointers to LBAs contained in the image.
It starts with the following header.
[source,c]
/* Undefined */
==== Field Descriptions
[cols="2,2,2,6",options="header"]
|===
|Type
|Size
|Name
|Description
|uint32_t
|4 bytes
|identifier
|The deduplication table identifier, always `DDT2` or `DDTS`. The first level of a table is always `DDT2` and its presence is mandatory. Subtables will have `DDTS`
|uint16_t
|2 bytes
|type
|The data type pointed by this table. See Annex B.
|uint16_t
|2 bytes
|compression
|The compression algorithm used in the table. See Annex C.
|uint8_t
|1 byte
|levels
|How many levels of subtables are present. 1 means this is the only level.
|uint8_t
|1 byte
|tableLevel
|What level does this table correspond to
|uint64_t
|8 bytes
|previousLevel
|Pointer to absolute byte offset in the image file where the previous table level resides
|uint16_t
|2 bytes
|negative
|The negative displacement of LBA numbers. For media that can have negative LBAs, this establishes the number to substract to the table entry number
|uint64_t
|8 bytes
|start
|The first LBA contained in this table. It must be 0 for ‘DDT2’ blocks and can be other number for subtables ‘DDTS’
|The size in bytes of the compressed table that follows this header.
|uint32_t
|4 bytes
|length
|The size in bytes of the table block when decompressed.
|uint64_t
|8 bytes
|cmpCrc64
|The CRC64-ECMA checksum of the compressed table that follows this header.
|uint64_t
|8 bytes
|crc64
|The CRC64-ECMA checksum of the decompressed table.
|===
The size type defines the following type of entries:
[cols="1,1,6",options="header"]
|===
|Type
|Value
|Description
|Mini
|0
|Each entry uses two bytes, with the leftmost byte (mask 0xFF00) used for flags, and the rightmost byte used as a pointer to the sector or next level.
|Small
|1
|Each entry uses three bytes, with the leftmost byte used for flags and the next two bytes used as a pointer to the sector or next level.
|Medium
|2
|Each entry uses four bytes, with the leftmost byte (mask 0xFF000000) used for flags and the next three bytes used as a pointer to the sector or next level.
|Big
|3
|Each entry uses five bytes, with the leftmost byte used for flags and the next three bytes used as a pointer to the sector or next level.
|The sector is MODE 1 and the suffix or prefix is correct and can be regenerated. Must only appear on deduplications tables with types CdSectorPrefixCorrected or CdSectorSuffixCorrected
|Mode2Form1Ok
|`0x04`
|The suffix for MODE 2 sectors is correct, can be regenerated, and corresponds to a MODE 2 Form 1 sector. Must only appear on deduplications tables with type CdSectorSuffixCorrected
|Mode2Form2Ok
|`0x05`
|The suffix for MODE 2 sectors is correct, can be regenerated, and corresponds to a MODE 2 Form 2 sector with a valid CRC. Must only appear on deduplications tables with type CdSectorSuffixCorrected
|Mode2Form2NoCrc
|`0x06`
|The suffix for MODE 2 sectors is correct, can be regenerated, and corresponds to a MODE 2 Form 2 sector with an empty CRC. Must only appear on deduplications tables with type CdSectorSuffixCorrected
|Twin
|`0x07`
|The pointer contains a “twin” sector table (see below)
|Unrecorded
|`0x08`
|The sector was unrecorded and each re-read returns random data
|===
When flags are present in a table that has sublevels it applies to all the sectors that shall be present in the subtable, unless the flag specify something else.
