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Module arsenic

compcol

Module arsenic 

Source
Available on crate feature arsenic only.
Expand description

StuffIt 5 Arsenic (compression method 15) — decoder only.

Arsenic is the Burrows–Wheeler-based codec used by StuffIt 5 archives (compression-method id 15). This module decodes the raw method-15 fork payload — the bytes a StuffIt 5 container stores for a member compressed with Arsenic — not the SIT container itself. It plugs in behind the streaming crate::traits::Algorithm trait like the other per-method codecs in this crate.

§Decode pipeline

  1. A carry-less binary range/arithmetic decoder (NUMBITS = 26, ONE = 2^25, HALF = 2^24, MSB-first bit feed) driving nine adaptive frequency models recovers a stream of selector/symbol tokens.
  2. The tokens drive a combined un-RLE / un-MTF stage (a bijective base-2 zero-run scheme for runs of MTF index 0) producing one block of BWT-permuted bytes.
  3. An inverse Burrows–Wheeler transform un-permutes the block using a stored primary index.
  4. If the block is flagged randomized, selected byte positions are XOR-corrected at spacings drawn cyclically from a fixed 256-entry randomization table.
  5. A final “four equal bytes then count” RLE layer is expanded.

The stream self-terminates: each block carries an end-of-blocks flag and the final block is followed by a 32-bit CRC-32 trailer (poly 0xEDB88320, init 0xFFFFFFFF, compared to the bitwise complement of the running CRC over the decoded output). No out-of-band length is required.

§Encoder

Permanently Error::Unsupported: StuffIt 5 is a decode-only target in this crate (matching LZFSE, Quantum, RAR*, …).

§Tables

The nine model parameters and the 256-entry randomization table are wire-format constants required for bit-exact decoding; they are embedded verbatim in tables from the project’s maintainer-sanctioned interoperability data.

Structs§

Arsenic
Zero-sized marker type implementing Algorithm for StuffIt 5 Arsenic.
Decoder
Streaming Arsenic decoder.
Encoder
Encoder stub. StuffIt 5 Arsenic encoding is out of scope for this build; every method here returns Error::Unsupported.