=== Twin Sector Table (`TWTB`)

This table enumerates hardware sectors that share an identical sector number.
Such sectors are referred to as “twin sectors,” although the grouping may consist of more than two instances.
The associated pointer is resolved following the same logic applied in a last-level deduplication table.

[source,c]
/* Undefined */

==== Field Descriptions

[cols="2,2,2,6",options="header"]
|===
|Type
|Size
|Name
|Description

|uint32_t
|4 bytes
|identifier
|The twin sector table identifier, always `TWTB`

|uint8_t
|1 byte
|alignment
|Shift of alignment of all blocks in the image. This must be the same in all deduplication tables and subtables.

|uint8_t
|1 byte
|shift
|The shift used to calculate the position of a sector in a data block pointed by this table, or how many sectors are pointed by the next level.

|uint64_t
|8 bytes
|entries
|How many pointers follow this header.

|uint32_t
|4 bytes
|length
|The size in bytes of the table block.

|uint64_t
|8 bytes
|crc64
|The CRC64-ECMA checksum of the decompressed table.
|===

==== Twin sector entries

[cols="2,2,2,6",options="header"]
|===
|Type
|Size
|Name
|Description

|uint32_t
|8 bytes
|pointer
|Pointer to the sector.
|===

==== Pointer-Based Data Block Resolution

To determine the corresponding data block:

. Right-shift the pointer value using the specified `shift` parameter.
. Multiply the result by the `alignment` value.
. The remainder from this operation indicates the sector's offset within the target data block.

Each data block contains a fixed number of bytes per sector, which remains constant across blocks.
This invariant size allows for more efficient storage of pointer values.

===== Example

Given the following parameters:

* Pointer Value: `0x8003`
* Shift Value: `5`
* Alignment: `9`

The data block is located at byte offset `524288`.
The sector referenced by the pointer is the **third entry** within this block.
