libmsxca

Cross-platform decompressor for Xbox Compression LZXNATIVE (magic 0FF512EE) Xbox 360 XMemCompress / Xbcompress files.

What it does

Decompresses Xbox 360 compressed data blobs that use the Xbox Compression "LZXNATIVE" codec — the format produced by Microsoft's xcompress.dll and xbcompress.exe tools. These blobs are commonly found inside LNK4 game containers (e.g. from "11eyes CrossOver" and other Xbox 360 titles). The library itself is basically a wrapper on top of libmspack.

The library handles the full decoding pipeline:

1. Validates the 48-byte big-endian header (magic 0FF512EE)
2. Parses window size, uncompressed size, and block-size fields
3. Iterates over compressed blocks, each preceded by a 4-byte BE size
4. Strips the 2-byte BE chunk-framing length prefixes from each block's data
5. Feeds the deframed data to libmspack's LZX (lzxd) decoder with a fresh decode context per block
6. Returns the fully decompressed output

What it does NOT do

Compression / recompression is not supported. There is no open-source or cross-platform LZXNATIVE encoder. Recompression requires Microsoft's proprietary xcompress.dll (XMemCompress) on Windows.

The origin of the project

Every pure-managed LZX decompression port tested (XMemCompressionDotNet, MonoGame LzxDecoder, cabextract-derived decoders) fails on the Xbox Compression chunk framing or has a separate decode bug. libmspack's lzxd, used with chunk-deframing and a fresh decode context per block (reset_interval = 0, output_length = UncompressedBlockSize), decodes blobs byte-identically to the native codec.

The library name is a shorthand for "Xbox (360) Compression Algorithm", also coincidentally similar to the Xpress compression format reference doc's name, but that one wasn't useful for the project.

Tested with

Building platform	Result
Linux (gcc, clang)	Builds and passes
macOS (clang)	Builds and passes
Windows (MSVC)	Builds and passes
Windows (mingw64 cross-compile)	Builds and passes

Tested games

Game resource	Result
elevene-system.dat (LNK4, 11eyes CrossOver)	38/38 compressed blobs decoded, SHA-256 verified against source files
sg-system.dat (LNK4, SteinsGate Xbox 360)	61/61 entries, SHA-256 verified against source files

• Note that there could be differences with untested games.

Note

• OpenCode's Zen models were used during the development and testing phase for this library.

License

• libmsxca wrapper (msxca.c, msxca.h): MIT — do what you want
• libmspack (lzxd.c, lzx.h, mspack.h, system.h, system.c, macros.h, readbits.h, readhuff.h): LGPL 2.1 — see COPYING.LIB (libmspack by Stuart Caie)

References

• LZX Delta documentation, also referred as "[MS-PATCH]"
• Microsoft LZX Data format, the Cabinets reference