MPQ
| Filename extension | .mpq |
|---|---|
| Developed by | Mike O'Brien |
MPQ (Mo'PaQ, short for Mike O'Brien Pack, named after its creator), is an archiving file format used in several of Blizzard Entertainment's games.
MPQs used in Blizzard's games generally contain a game's data files, including graphics, sounds, and level data. The format's capabilities include compression, encryption, file segmentation, extensible file metadata, cryptographic signature and the ability to store multiple versions of the same file for internationalization and platform-specific differences. MPQ archives can use a variety of compression algorithms which may also be combined.
In order to meet the requirements of speed generally demanded by a computer game, files are indexed in a hash table using a quick, low-collision hashing algorithm. The index of a specific file within the hash table is the hash of the lowercased filename modulo the size of the hash table, allowing for quick verification of a file's existence within the archive. If multiple files within the archive have the same hash, colliding entries will follow each other in increasing index order (forming a colliding hash cluster). In order to identify the exact entry for the requested file within a colliding hash cluster, each hash table entry stores 2 additional hashes of the lowercased filename, each using the same hashing algorithm but with a different seed value, as well as a locale code and platform code. The end of a colliding hash cluster is detected either by encountering an empty hash table entry or by traversing the entire hash table (including the modulo loopback) back to the initial hash table index.
Both the block table (which contains information on where the file data is located in the archive) and the hash table used for file indexing are encrypted when stored. The encryption process which is used by default uses a known algorithm.
The file header reserves space to contain format version data. Warcraft III ignores format version data of .mpq compliant files it loads and assumes all are version 1.
MPQ archives do not have specific structures to store metadata beyond what is absolutely necessary to access archived files. Instead, the convention is to use regular files whose filename is enclosed by parentheses.
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