MPQ

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MPQ File Header and MPQ File Shunt

Great majority of file format begins with a header and MPQ format is no exception. Size of MPQ header is at least 32 bytes (0x20). When processing MPQ, the application looks at every offsets 0, 0x200, 0x400, 0x600, and so on, until the header has been found or until the end of the file has been reached. This feature allows to store the MPQ archives into other file types, e.g. into EXE files. Install.exe on StarCraft or BroodWar installation CD are actually MPQ archives. At this offset, there may either be MPQ header or a MPQ shunt. This is determined by the 32-bit ID:

  • 'MPQ\x1A' means there's MPQ header at that offset
  • 'MPQ\x1B' means there's MPQ shunt structure at that offset

MPQ Shunt

Offset Type Name Description
0x00 uint32 Magic The ID_MPQ_SHUNT ('MPQ\x1B') signature
0x04 uint32 Unknown
0x08 uint32 HeaderPosition Position of the MPQ header, relative to the begin of the shunt

MPQ Header

Offset Type Name Description
0x00 uint32 Magic The ID_MPQ_SHUNT ('MPQ\x1A') signature
0x04 uint32 HeaderSize
0x08 uint32 ArchiveSize
0x0C uint16 FormatVersion 0 = Original format, 1 = Extended format (The Burning Crusade and newer)
0x10 uint16 BlockSize
0x12 uint32 HastTablePosition Relative to the beginning of the archive
0x14 uint32 BlockTablePosition Relative to the beginning of the archive
0x18 uint32 HashTableSize
0x1C uint32 BlockTableSize

Extended MPQ Header

Extended MPQ file header. Valid only if FormatVersion is 1 or higher

Offset Type Name Description
0x00 uint64 ExtBlockTablePos Offset to the beginning of the extended block table, relative to the beginning of the archive.
0x08 uint16 HashTablePosHigh High 16 bits of the hash table offset for large archives.
0x0A uint16 BlockTablePosHigh High 16 bits of the block table offset for large archives.

Hash Table

When searching large array of strings, it is necessary to do large number of string comparisons, which slows the application. To prevent this, MPQ archives contain so called hash table. Hash is a data type (integer), which represents larger data, e.g. string. Searched string is recalculated into hash value (32-bit integer), which is the compared. This means that there are no file names stored in the MPQ archives. And because the hashing algorithm is one way (it's impossible to get back the original string value), it is also no way to search the file names in the archive. Hash table in the MPQ contains also two control hash values as test for the file name, one control value and a offset info block table. Size of one entry of hash table is 16 bytes. The structure of hash table is the following:

Offset Type Name Description
0x00 uint32 Name1
0x08 uint32 Name2
0x0C uint16 Locale The language of the file. This is a Windows LANGID data type, and uses the same values
0x0E uint16 Platform The platform the file is used for. 0 indicates the default platform.
0x10 uint32 BlockIndex If the hash table entry is valid, this is the index into the block table of the file.

Block Table

Block table contains informations about file sizes and way of their storage within the archive. It also contains the position of file content in the archive. Size of block table entry is (like hash table entry). The block table is also encrypted. The entry in the block table has the following structure:

Offset Type Name Description
0x00 uint32 FilePosition
0x08 uint32 compressedSize
0x0C uint32 uncompressedSize
0x10 uint32 Flags The platform the file is used for. 0 indicates the default platform.



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