Changelog

All notable changes are listed here. The format follows Keep a Changelog and versions follow Semantic Versioning.

Unreleased

0.7.0-preview.1 - 2026-10-29

Everything is still preview and carries [Experimental]. No codec changed since 0.5.1-preview.1, so the README measurements stand. Version 0.6 is reserved for RAR compressed entries.

Added

• Microsoft compound file writer (CompoundFileWriter, CompoundFileWriterOptions): versions 3 and 4, FAT, DIFAT, mini stream, red-black directory trees, CLSIDs, state bits and times, reachable as Archive.Create("x.cfb") (docs/cfb.md).

0.5.1-preview.1 - 2026-10-29

Everything is still preview and carries [Experimental]. The README has the new measurements from both machines.

Changed

• Deflate, zlib and gzip: faster one-shot and streaming compression at levels 1-9. The greedy and lazy parsers no longer store literals and the block writer emits literal runs straight from the input (identical bytes by itself); levels 1-3 and 5-9 use shallower hash-chain searches (level 1 enters fewer positions of long matches, levels 6-9 also give up on the lazy look-ahead sooner), so their compressed bytes differ from 0.5 while staying within 1% of libdeflate's size. Levels 0, 4 and 10-12 and Deflate64 are unchanged.
• Zstandard: levels 5-9 (and 6-8 for sources of 128-256 KiB) enter only every fourth position that a long match skips over into the match table, which saves writes to a table far larger than the cache. Compressed bytes change, within 0.2% in size, and stay identical on every platform.
• LZ4: faster high-compression levels (3-12) through a tighter search, and a lazy level 2 that is within 0.2% of the lz4 tool's size (it was +2.2%). Levels 3-9 search deeper where no match is known yet and only briefly for a longer match one or two bytes later, and take a match of 64 bytes or more without looking further; this makes them 8-19% faster at about the same size. Levels 2-9 are retuned, so their compressed bytes differ from 0.5 while staying within 1% of the tool's size; levels 1 and 10-12 are unchanged.
• Zstandard: levels 1-2 compress 3-11% faster (most on text), with identical output.
• Zstandard dictionary training: COVER and fast-COVER training is 3-9 times faster and uses 4-12 times less memory (a 1024 x 8 KiB sample set trains in under a second in under 100 MiB, from 6.6 s and 1.2 GiB). D-mers are counted once per size and the parameter search is guided; sets up to 256 KiB are searched exhaustively. The new SearchMode option selects the search. Trained dictionaries differ from 0.5 (still identical on every platform and thread count) and compress held-out game data within about 1% of the previous ones and of zstd --train (the worst case is +1.2% against the tool, at a 4 KiB dictionary).
• Zstandard: levels 10-15 compress 25-45% faster. Levels 10-12 search one step less deep than the zstd tool, so their bytes change (within 0.6% in size); levels 13-15 are unchanged.

Added

• Microsoft compound file reader (CompoundFileReader, ArchiveFormat.CompoundFile): .doc, .xls, .ppt and .msg containers, versions 3 and 4, with strict validation and Archive support (docs/cfb.md).
• bench/Managed: compares each codec with the fastest managed .NET implementations (ZstdSharp, K4os, SharpCompress and others), reporting speed and size per row.
• THIRD-PARTY-NOTICES.md: an entry for the RFC 8878 code tables used by the Zstandard codec.

0.5.0-preview.1 - 2026-10-29

Everything is still preview and carries [Experimental]. The README has the new measurements from both machines.

Changed

• Deflate64: a fast decode loop; decompression now runs at 2.0-2.6 times the speed of 7-Zip's on both machines.
• PPMd: encoding and decoding are 1.4-1.6 times faster, with identical output. Decoding now runs at 0.89-0.95 of 7-Zip's speed and encoding at 0.85-0.91.
• LZMA, LZMA2, xz and lzip: faster decoding (fewer unpredictable branches per symbol), with identical output.
• Brotli: faster encoding at qualities 0-5 (quality 0 is about 1.5 times as fast as in 0.4). Qualities 0-2 now find matches and emit symbols in one pass, so their compressed bytes differ from 0.4 while staying within 1% of the brotli tool's size; qualities 3-11 are unchanged.
• Zstandard: levels 1-4 compress 2-10% faster, with identical output.

Fixed

• Zstandard: negative compression levels could write invalid frames on large inputs. A sequence whose state and extra bits filled the encoder's 64-bit bit container exactly was written twice, so the zstd tool and this library's decoder rejected the frame or decoded garbage. The same defect could in principle affect any level; it showed first at negative levels on the Silesia corpus. Frames that were valid are unchanged byte for byte.

0.4.0-preview.1 - 2026-10-29

Everything new here is preview and carries [Experimental]. The README has the measurements against the reference tools on both machines, misses included.

Added

• PPMd (ONECOMPRESS010): variants H and I as PpmdH/PpmdI, encoders, decoders and PpmdStream, byte-identical to 7-Zip's output; zip method 98 and the 7z PPMD coder, read and write. The codec is ported from the public-domain reference sources (see THIRD-PARTY-NOTICES.md). Levels 8 and 9 use 128 and 256 MiB of model memory, as 7-Zip does on large inputs. New limit ArchiveLimits.MaxPpmdMemorySize (256 MiB). See docs/ppmd.md.
• ISO 9660 read and write, with Joliet and Rock Ridge (docs/iso.md).
• RAR 5 (read only): list and metadata, stored entries, multi-volume sets; compressed entries raise a typed error. RAR 4 archives and header-encrypted archives are also refused with a typed error.
• Codec registration for the archive layer: by default every codec is available, and an app that wants a smaller trimmed or NativeAOT binary sets the RecursiveAI.OneArchive.AllCodecs feature switch to false and registers only the codecs it uses with ArchiveCodecs. A missing codec raises ArchiveUnsupportedException naming the format, the method and the call to add. A .tar.zst-only NativeAOT app shrank from 3.82 to 3.07 MB, without the brotli dictionary (docs/archive-codecs.md).
• Benchmarks against the reference tools for brotli, bzip2 compress, Deflate64, LZX and PPMd.

Changed

• Brotli: faster decoder (a fast command loop) and a much faster encoder at every quality: a bucketed match finder, a fused meta-block writer for qualities 0-5, smaller tables. Qualities 0-9 are still below the tool's speed (see the README). Compressed bytes at qualities 0-9 differ from 0.3, still identical on every platform.
• bzip2 encoder: about twice as fast (two-phase block sort, vector move-to-front, incremental table choice); on x64 it now runs at 1.11-1.14 of bzip2. Compressed bytes are unchanged.
• Deflate64 encoder: levels 5-9 use an optimal parse with block splitting, and levels 1-4 share one fast class; output is smaller at levels 4-9.
• Deflate64, bzip2, PPMd, AES and ZipCrypto entries in zip, and the 7z Deflate64, PPMd and AES-256 coders (including encrypted headers), are covered by interop tests with 7-Zip and Info-ZIP. AES needs System.Security.Cryptography.Aes, which the browser does not provide; there only ZipCrypto reading works.

Not supported

• BCJ2 in 7z is listed but refused with a typed "unsupported method" error. Quantum cabinets and cabinets that span files are refused with a typed error.

0.3.0-preview.1 - 2026-10-28

Everything new here is preview and carries [Experimental]. The LZMA family meets the size target and is below the reference speed in some rows; the README has the measurements from both machines.

Added

• Brotli (RFC 7932, ONECOMPRESS008): decoder with the built-in dictionary and transforms, and encoder at qualities 0-11 (windows 10-24), in three layers. Single streams .br and .tar.br in the archive layer, detected by file name (brotli streams have no magic number).
• bzip2 encoder at levels 1-9 (ONECOMPRESS004), zip method 12 writing, and .bz2/.tar.bz2 writing.
• Deflate64 decoder and encoder (ONECOMPRESS003), Deflate64Stream, zip method 9 read and write, and the 7z Deflate64 coder.
• LZX decoder (ONECOMPRESS009) with verbatim, aligned and uncompressed blocks and call translation.
• 7z writing: solid and non-solid folders, LZMA2, LZMA, Copy, Deflate and Zstandard coders, the branch and delta filters, and encoded headers.
• cpio (newc, crc and odc) and ar (common, GNU and BSD) read and write.
• cab read: stored, MSZIP and LZX folders, every header field, checksums, and a typed error for spanned cabinets and Quantum.
• xz and lzip single streams: .xz, .lz, .tar.xz and .tar.lz, read and write.
• Encryption (ONEARCHIVE001): zip WinZip AES-128/192/256 (AE-1 and AE-2) read and write, traditional zip encryption read; 7z AES-256 read and write, with encrypted headers. ZipReaderOptions.Password, ZipWriterOptions.Password, SevenZipReaderOptions.Password, SevenZipWriterOptions.Password, and Password on ArchiveOpenOptions and ArchiveCreateOptions. A missing or wrong password is an ArchivePasswordException. AES needs System.Security.Cryptography.Aes, which the browser does not provide.

Changed

• LZMA-family speed: decoder fast paths and match-finder prefetching. Deflate speed: a faster decoder loop and table build, and faster encoder levels 1-7. Deflate levels 2-4 now hash four bytes, so their output differs from 0.2 (still identical on every platform); other compressed bytes are unchanged.
• 7z reading: empty-stream vectors in the order the format defines, and coders without streams.

Not supported

• PPMd (zip method 98, 7z PPMD) and BCJ2 are listed but refused with a typed "unsupported method" error.

0.2.0-preview.1 - 2026-10-28

Everything new here is preview and carries [Experimental]. Deflate, zlib and gzip meet the size target and are below the reference speed; the bzip2 decoder meets both. The README has the measurements.

Added

• Deflate (RFC 1951), zlib (RFC 1950) and gzip (RFC 1952): decoder and encoder at levels 0-12 with strategies, preset dictionaries and flushes, in three layers (ONECOMPRESS003).
• bzip2 decoder: multi-stream and randomized blocks, with limits for hostile input (ONECOMPRESS004).
• LZMA and LZMA2 (ONECOMPRESS005), xz with CRC32, CRC64 and SHA-256 checks, the branch filters (x86, ARM, ARM-Thumb, ARM64, PowerPC, SPARC, IA-64, RISC-V) and Delta (ONECOMPRESS006), and lzip (ONECOMPRESS007): decoders and encoders at every preset.
• OneArchive (ONEARCHIVE001): Archive.Open, Archive.Extract and Archive.Create, with detection by content, extraction that never writes outside the target, and limits on size, ratio, entry count, path length and nesting.
  • tar: v7, ustar, pax and GNU (long names, sparse files), read and write.
  • zip: read and write with store, Deflate and Zstandard, zip64 and data descriptors; LZMA, xz and bzip2 entries read.
  • 7z: read, with Copy, Deflate, BZip2, LZMA, LZMA2, Delta, the branch filters and Zstandard, solid folders and encoded headers.
  • Single streams: gz, zst and lz4 (read and write) and bz2 (read), and tar inside them.
• Lz4BlockEncoder, a reusable block compressor, and a length-prefixed block form read back by Lz4PrefixedBlock (not an LZ4 frame). Lz4Dictionary.Train.
• ZstdCompressionDictionary.ForDecompression and ToArray, so one trained dictionary serves both directions.
• ZstdCompressionOptions.SizeHint: an estimate of a stream's length that sizes the window and tables without being written to the frame.

Changed

• Zstandard encoder memory: a stream of unknown length no longer reserves its whole window and binary-tree tables up front (level 22 took 384 MiB for a 1 KiB frame, 640 MiB with a small dictionary; now 129 MiB), and a dictionary's search index is sized by the dictionary, not the source (4 KiB at level 22: 256 MiB, now under 1 MiB). Compressed bytes are unchanged.
• Zstandard and Deflate speed work; compressed bytes of Zstandard are unchanged.

Not supported

• PPMd (zip method 98, 7z PPMD), BCJ2, Deflate64 and encryption are listed but refused with a typed "unsupported method" error.

0.1.0-preview.1 - 2026-10-28

First preview. Both codecs are preview and their public types carry [Experimental] (ONECOMPRESS001 for Zstandard, ONECOMPRESS002 for LZ4): compressed sizes are at or near the reference tools', and speed is still below them. The README has the measurements.

Added

• Zstandard (RFC 8878): every level from -7 to 22, frames and skippable frames, dictionaries (raw and formatted), dictionary training, long-distance matching, multithreaded compression in fixed-size jobs (the same bytes at any thread count), and the seekable format. One-liners on Zstd; ZstdEncoder/ZstdDecoder over spans with OperationStatus, and ZstdStream; the parts beneath (FSE and Huffman tables, match finders, block writer) are public.
• LZ4 block and frame formats, fast and high-compression levels, with dictionaries and linked blocks, in the same three layers.
• Checksums: CRC32, CRC32C, CRC64, Adler-32 and xxHash64, with vector paths.
• Input is treated as untrusted: the Zstandard decoder caps the window it will allocate (8 MiB by default), malformed input is a typed error, and every decoder has a fuzz target.
• NativeAOT, trimming and browser WebAssembly are supported; output is byte-identical on every platform.