LZMA - LZMA Compressed File Format
What is a LZMA file?
A file with .lzma extension is a compressed archive file created using the LZMA (Lempel-Ziv-Markov chain Algorithm) compression method. These are mainly found/used on Unix operating system and are similar to other compression algorithms such as ZIP for minimising file size. LZMA is a legacy file format, which is being or has been replaced by the .xz format. The MIME type of the .lzma format is `application/x-lzma’. This file format was designed by Igor Pavlov for use in LZMA SDK.
LZMA File Format
The LZMA file consists of two main parts:
- Header
- Compressed Data
LZMA Header
The LZMA files has a 13-byte header that is followed by the LZMA compressed data. The LZMA header consists of:
- Properties
- Dictionary Size
- Uncompressed Size
LZMA Header Properties
The Properties field contains three properties. An abbreviation is given in parentheses, followed by the value range of the property. The field consists of
- the number of literal context bits (lc, [0, 8]);
- the number of literal position bits (lp, [0, 4]); and
- the number of position bits (pb, [0, 4]).
LZMA Dictionary Size
This is stored as an unsigned 32-bit little endian integer with values ranging from 2^n and 2^n + 2^(n-1). LZMA Utils can decompress files with any dictionary size.
Uncompressed Size
The Uncompressed Size is stored as unsigned 64-bit little endian integer. A special value of 0xFFFF_FFFF_FFFF_FFFF indicates that Uncompressed Size is unknown. The value is represented by End of Payload Marker (*) if and only if Uncompressed Size is unknown.