Hmm..., very interesting. The VOL files do support other compression formats. The compression code ranges from 0-3 (and it's only 1 byte). I'm not yet sure what the other codes do or what happens when a value above 3 is used. I've also found some interesting inheritance relationships between classes.
Layout of Internal Classes
--------------------------
Note: ClassA:ClassB denotes that ClassB is drived from ClassA. (Opposite to C++ convention)
StreamIO:???:VolFile
----------------
Note: VolFile derives (indirectly) from StreamIO. (Distance of 1)
Offset Size Description
------ ---- -----------
0x0 4 vtbl - 0x4D6B20
0x4 4
0x8 4 streamStatus - A nonzero value denotes an error
- - - - - - - - - - - - - - <- End of StreamIO base class variables
0xC 4 int numIndexEntries
0x10 4 IndexEntry *indexTable - allocated memory to hold index table
0x14 4 void *fileNameBuffer - buffer containing all internal file names as a list of NULL terminated strings
0x18 4 LPVOID mappedAddress - memory address of memory mapped file
0x1C 4 HANDLE fileMapping - handle to the file mapping object
0x20 4 HANDLE fileHandle - handle to opened VOL file
0x24 4 DWORD fileSize - size of the opened VOL file (-1 for unspecified)
0x28 4 StreamIO *decompressor - points to decompression object for opened stream (One of the contained objects below)
0x2C ? StreamIO:??? inputStream - input stream for all VolFile data?
0x44 ? StreamIO:Case0Decompressor (Uncompressed raw data)
0x64 ? StreamIO:Case1Decompressor (Unknown **TODO** explore this)
0xFC ? StreamIO:Case3Decompressor (AdaptiveHuffman+RepeatedBlocks)
0x128 ? StreamIO:Case2Decompressor (Unknown **TODO** explore this)
0x158 4 boolSetFileSize - if nonzero, sets the file size to fileSize variable when opened
0x160 ? (Internal object?)
Note: VolFile can have only one open stream at a time.
Note: VolFile derives from StreamIO and is useable to refer to it's opened stream
StreamIO
--------
Offset Size Description
------ ---- -----------
0x0 4 vtbl - 0x4D74FC
0x4 4
0x8 4 int streamStatus - A nonzero value denotes an error
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