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Add anm and pbg3 file formats, and improve the std one.
author Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>
date Tue, 02 Aug 2011 14:18:01 +0200
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children 2925b0e246c6
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0:f82309a9465e 1:b1bec4b5ccf3
1 <?xml version="1.0" encoding="utf-8"?>
2 <?xml-stylesheet type="text/css" href="../style.css"?>
3 <!DOCTYPE html>
4 <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
5 <head>
6 <title>PBG3 format</title>
7 </head>
8 <body>
9 <h1>PBG3 format</h1>
10 <p>The PBG3 format is an archive format used by EoSD.</p>
11
12 <p>It is a bitstream composed of a header, a file table, and LZSS-compressed files.</p>
13
14
15 <h2>Reading integers</h2>
16 <p>Integers in PBG3 files are never signed, they are not byte-aligned, and have a variable size.<br/>
17 Their size is given by two bits: 00 means the number is stored in one byte, 10 means it is stored in three bytes.</p>
18
19 <p>Ex:</p>
20 <pre>
21 0x0012 is stored as: 0000010010
22 0x0112 is stored as: 010000000100010010
23 </pre>
24
25
26 <h2>Reading strings</h2>
27 <p>Strings are stored as standard NULL-terminated sequences of bytes.<br/>
28 The only catch is they are not byte-aligned.</p>
29
30
31 <h2>Header</h2>
32 <p>The header is composed of three fields:</p>
33 <ul>
34 <li>magic (string): "PBG3"</li>
35 <li>number of entries (integer)</li>
36 <li>offset of the file table (integer)</li>
37 </ul>
38
39 <p>The size of the header is thus comprised between 52 bits and 100 bits.</p>
40
41
42 <h2>File table</h2>
43 <p>The file table starts at a byte boundary, but as the rest of the file, isn't byte-aligned.<br/>
44 It consists of a sequence of entries.<br/>
45 Each entry is composed of five fields:</p>
46 <ul>
47 <li>unknown1 (int) #TODO</li>
48 <li>unknown2 (int) #TODO</li>
49 <li>checksum (int): simple checksum of compressed data</li>
50 <li>size (int): size of uncompressed data</li>
51 <li>name (string): name of the file</li>
52 </ul>
53
54 <p>The checksum is a mere sum of the compressed data.<br/>
55 Files are compressed using the LZSS algorithm, with a dictionary size of 8192 bytes and a minimum matching length of 4 bytes.<br/>
56 The size of the offset component of (offset, length) tuples is 13 bits, whereas the size of the length component is 4 bits.<br/>
57 A file ends with a (0, 0) tuple, that is, 18 zero bits.</p>
58
59 <p>Uncompressing a LZSS-compressed file is quite easy, see lzss.py.</p>
60 </body>
61 </html>