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29 lines
1.1 KiB
Plaintext
29 lines
1.1 KiB
Plaintext
[appendix]
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== Compression Types
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This apprendix lists all supported compression algorithms used within AaruFormat images.
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NOTE: Compression method definitions may evolve over time.
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For the latest and most accurate listing, refer to the `libaaruformat` source.
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[cols="1,5",options="header"]
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|===
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|Value
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|Algorithm
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|0 |None
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|1 |LZMA — stream prepended by 5 bytes of parameters
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|2 |FLAC
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|3 |LZMA after Claunia Subchannel Transform (see Appendix D) — stream prepended by 5 bytes of parameters
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|4 |Zstandard (zstd) — standard zstd frame, no prefix
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|5 |Zstandard after Claunia Subchannel Transform (see Appendix D) — standard zstd frame, no prefix
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|===
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==== Notes on Zstandard (IDs 4 and 5)
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Unlike LZMA (IDs 1 and 3), Zstandard compressed payloads are stored as self-contained zstd frames.
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The `cmpLength` field in the block header covers the entire compressed payload with no additional prefix bytes.
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ID 5 (`ZstdCst`) applies the Claunia Subchannel Transform before compression and is restricted to blocks with data type `CdSubchannel`.
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This mirrors the constraint on ID 3 (`LzmaCst`).
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