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79 lines
1.9 KiB
Plaintext
79 lines
1.9 KiB
Plaintext
=== Index Block version 2 (`IDX2`)
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The index block stores references to all blocks present in the file.
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It is composed of a header, followed by a sequence of entries, the count of which is defined within the header.
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Multiple index blocks may exist within a file to represent previous states or historical versions; however, only the final index block must be referenced by the main file header.
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==== Structure Definition
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[source,c]
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#define INDEX2_MAGIC 0x32584449
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/**Header for the index, followed by entries */
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typedef struct IndexHeader2
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{
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uint32_t identifier; ///< Block identifier (must be BlockType::IndexBlock2).
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uint64_t entries; ///< Number of \ref IndexEntry records that follow immediately.
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uint64_t crc64; ///< CRC64-ECMA of the entries array (legacy byte-swapped rule still applies for old versions).
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} IndexHeader2;
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==== Field Descriptions
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[cols="2,2,2,6",options="header"]
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|===
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|Type
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|Size
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|Name
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|Description
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|uint32_t
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|4 bytes
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|identifier
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|The index block identifier, always `IDX2`
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|uint64_t
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|8 bytes
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|entries
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|The number of entries following this header
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|uint64_t
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|8 bytes
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|crc64
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|CRC64-ECMA checksum of the entries following this header
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|===
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==== Index entries
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[source,c]
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/**Index entry */
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typedef struct IndexEntry
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{
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uint32_t blockType; ///< Block identifier of the referenced block (value from \ref BlockType).
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uint16_t dataType; ///< Data classification (value from \ref DataType) or unused for untyped blocks.
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uint64_t offset; ///< Absolute byte offset in the image where the referenced block header begins.
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} IndexEntry;
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==== Field Descriptions
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[cols="2,2,2,6",options="header"]
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|===
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|Type
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|Size
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|Name
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|Description
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|uint32_t
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|4 bytes
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|blockType
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|The type of block this entry points to.
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|uint32_t
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|2 bytes
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|dataType
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|The type of data the block pointed by this entry contains.
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|uint64_t
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|8 bytes
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|offset
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|The offset in bytes from the start of the file where the block pointed by this entry starts.
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|=== |