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[Specification] Add data block definition (DBLK)

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Natalia Portillo
2025-07-31 15:14:35 +01:00
parent 25de94a998
commit 3e2ce1c665
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docs/spec/spec.adoc
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include::structs/index_continuation.adoc[]
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include::structs/data.adoc[]

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=== The data block (`DBLK`)
A data block encapsulates media-derived content and is composed of a header followed by either compressed or uncompressed data.
The contents of a data block may represent user data—such as media sectors—or auxiliary data elements, including media or sector-specific tags.
When a data block includes multiple items (e.g., sectors or sector tags), the `sectorSize` field specifies the size, in bytes, of each individual item.
Conversely, if the block contains a single item (e.g., media tags), `sectorSize` must be set to 0.
==== Structure Definition
[source,c]
#define DATABLOCK_MAGIC 0x4B4C4244
/**Block header, precedes block data */
typedef struct BlockHeader
{
/**Identifier, <see cref="BlockType.DataBlock" /> */
uint32_t identifier;
/**Type of data contained by this block */
uint32_t type;
/**Compression algorithm used to compress the block */
uint16_t compression;
/**Size in uint8_ts of each sector contained in this block */
uint32_t sectorSize;
/**Compressed length for the block */
uint32_t cmpLength;
/**Uncompressed length for the block */
uint32_t length;
/**CRC64-ECMA of the compressed block */
uint64_t cmpCrc64;
/**CRC64-ECMA of the uncompressed block */
uint64_t crc64;
} BlockHeader;
==== Field Descriptions
[cols="2,2,2,6",options="header"]
|===
|Type
|Size
|Name
|Description
|uint32_t
|4 bytes
|identifier
|The data block identifier, always `DBLK`
|uint16_t
|2 bytes
|type
|The data type contained in this block. See Annex B.
|uint16_t
|2 bytes
|compression
|The compression algorithm used in the data. See Annex C.
|uint32_t
|4 bytes
|sectorSize
|The size in bytes of the sectors contained in this data block if applicable.
|uint32_t
|4 bytes
|cmpLength
|The size in bytes of the compressed data that follows this header.
|uint32_t
|4 bytes
|length
|The size in bytes of the data block when decompressed.
|uint64_t
|8 bytes
|cmpCrc64
|The CRC64-ECMA checksum of the compressed data that follows this header.
|uint64_t
|8 bytes
|crc64
|The CRC64-ECMA checksum of the decompressed data.
|===