**=====================**
   //                       \\
  //    Vanaheim Project     \\
 //                           \\
||  vanaheimproject@gmail.com  ||
 \\                           //
  **=========================**
      GRF alpha File Format
     by flaviojs @ April 2007
  **=========================**



This version is used by the alpha and beta1 clients.
A Grf file contains files and folders. File contents can be compressed or not.
All the data is in Little endian format.



  ==((   Grf descriptor    ))==

At the end of the file there are 9 bytes that describe where the entry list is 
located, the number of entries and the version of the format being used:

<entry_list_off>.4B <num_entries>.4B <version_maybe>.B [EOF]

'entry_list_off' is where the entry list starts, relative to the start of the file

'num_entries' has the upper and lower words (2 bytes) switched
num_entries = ( num_entries << 16 ) | ( num_entries >> 16 );

'version' is the version of the grf? always 0x12
TODO check which grf versions exist



  ==((     Entry list      ))==

List of 'num_entries' entries (folders and files) in the grf.
The list starts at offset 'entry_list_off'.
Each entry has variable size and uses the format:

<name_len>.B <type>.B <offset>.4B <packed_size>.4B <real_size>.4B <name>.?B

'name_len' is the length of the name, excluding the null terminator

'type' determines if it's a directory or a fie and if it's compressed or not:
type=0 : file (raw, uncompressed)
type=1 : file (compressed)
type=2 : directory

'offset' is where the data starts in the grf, 0 for directories

'packed_size' is the size of the data in the grf, 0 for directories

'real_size' is the size of the data after uncompression, 0 for directories

'name' is the pathname of the entry with the half bytes switched
name[i] = ( name[i] << 4 ) | ( name[i] >> 4 );
The length of this field is 'name_len' + 1 for the null terminator (a 00 byte 
at the end).
All directories in this pathname are separated by '/' and need to have it's 
entries before.
Example:
  the directory entry "data" needs to be before the directory entry "data/texture",
  which needs to be before the file entry "data/texture/some_file.bmp"



  ==((     Compression     ))==

The compression method is a derivative of LZSS. [1]
It has a dictionary window of 4096 bytes (12 bits) and a maximum match length 
of 15 (4 bits) + 2 (minimum encoding length).
The main difference is that the coded/unencoded flags are agregated in groups 
of 8 (1 byte).

TODO extended description



  ==((     Bibliography    ))==

[1] http://en.wikipedia.org/wiki/LZSS
    http://michael.dipperstein.com/lzss/