aaru-dps/libaaruformat
1
0
Fork 0
mirror of https://github.com/aaru-dps/libaaruformat.git synced 2026-09-21 06:14:17 +00:00
Code Issues 3 Packages Projects Releases Wiki Activity

Merge pull request #16 from RomTholos/fix/spec-ddt2-alignment-formula

Browse Source 
Fix/spec ddt2 alignment formula
This commit is contained in:
Natalia Portillo
2026-03-29 17:53:23 +01:00
committed by GitHub
parent 94d2c6e67e d9c1c9d607
commit c2e71490df
2 changed files with 9 additions and 9 deletions
Download Patch File Download Diff File Expand all files Collapse all files

12
docs/spec/blocks/ddt2.adoc
View File

@@ -141,7 +141,7 @@ These parameters are stored in both the master header and each deduplication tab
===== Block Alignment
Each block in the image is aligned to a boundary of `2 << block_alignment_shift`.
Each block in the image is aligned to a boundary of `1 << block_alignment_shift`.
This alignment is essential for technical consistency and performance.
===== Table Shift
@@ -157,10 +157,10 @@ For example:
| Sectors per Entry
| 1
| (2 << table_shift)^2 = 262144
| (1 << table_shift)^2 = 262144
| 2
| 2 << table_shift = 512
| 1 << table_shift = 512
| 3
| 1
@@ -175,7 +175,7 @@ In non-terminal levels (i.e., all except the last), each entry contains:
- Relevant metadata flags for its sector range
- An offset pointing to the next deduplication level
To obtain the byte offset in the image file, multiply this offset by `2 << block_alignment_shift`.
To obtain the byte offset in the image file, multiply this offset by `1 << block_alignment_shift`.
In the last level, the `data_shift` is applied as follows to determine the specific item within a data block:
@@ -191,13 +191,13 @@ Step 1: Mask and shift
0x35006 >> 5 = 0x1A80
Step 2: Compute byte offset
0x1A80 * (2 << 9) = 0x6A0000
0x1A80 * (1 << 9) = 0x350000
Step 3: Determine item index
0x35006 & 0x1F = 6
Result:
Sector is stored at byte offset 0x6A0000 as item number 6 in the data block.
Sector is stored at byte offset 0x350000 as item number 6 in the data block.
----
===== Deduplication Table Status

6
docs/spec/blocks/header.adoc
View File

@@ -53,9 +53,9 @@ A bump indicates potential breaking changes.
| guid | uint8_t[GUID_SIZE] | Globally Unique Identifier (GUID) that allows linking of related image derivatives and child snapshots.
Length is defined by `GUID_SIZE`.
| blockAlignmentShift | uint8_t | Determines block alignment boundaries using the formula 2 << blockAlignmentShift.
| dataShift | uint8_t | Determines the maximum number of data items in a block using the formula 2 << dataShift.
| tableShift | uint8_t | Shift used to calculate the number of sectors in a deduplication table entry, using the formula 2 << tableShift.
| blockAlignmentShift | uint8_t | Determines block alignment boundaries using the formula 1 << blockAlignmentShift.
| dataShift | uint8_t | Determines the maximum number of data items in a block using the formula 1 << dataShift.
| tableShift | uint8_t | Shift used to calculate the number of sectors in a deduplication table entry, using the formula 1 << tableShift.
| featureCompatible | uint64_t | Bitmask of features that, even if not implemented, still allow reading and writing the image.
| featureCompatibleRo | uint64_t | Bitmask of features that allow read-only processing of the image if unsupported.