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		<title>PBG3 format</title>
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		<h1>PBG3 format</h1>
		<p>The PBG3 format is an archive format used by EoSD.</p>

		<p>It is a bitstream composed of a header, a file table, and LZSS-compressed files.</p>


		<h2>Reading integers</h2>
		<p>Integers in PBG3 files are never signed, they are not byte-aligned, and have a variable size.<br/>
		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>

		<p>Ex:</p>
<pre>
    0x0012 is stored as: 0000010010
    0x0112 is stored as: 010000000100010010
</pre>


		<h2>Reading strings</h2>
		<p>Strings are stored as standard NULL-terminated sequences of bytes.<br/>
		The only catch is they are not byte-aligned.</p>


		<h2>Header</h2>
		<p>The header is composed of three fields:</p>
		<ul>
			<li>magic (string): "PBG3"</li>
			<li>number of entries (integer)</li>
			<li>offset of the file table (integer)</li>
		</ul>

		<p>The size of the header is thus comprised between 52 bits and 100 bits.</p>


		<h2>File table</h2>
		<p>The file table starts at a byte boundary, but as the rest of the file, isn't byte-aligned.<br/>
		It consists of a sequence of entries.<br/>
		Each entry is composed of five fields:</p>
		<ul>
			<li>unknown1 (int): the same for every entry of an archive, and without much change between two archives #TODO</li>
			<li>unknown2 (int) #TODO</li>
			<li>checksum (int): simple checksum of compressed data</li>
			<li>size (int): size of uncompressed data</li>
			<li>name (string): name of the file</li>
		</ul>

		<p>The checksum is a mere sum of the compressed data.<br/>
		Files are compressed using the LZSS algorithm, with a dictionary size of 8192 bytes and a minimum matching length of 4 bytes.<br/>
		The size of the offset component of (offset, length) tuples is 13 bits, whereas the size of the length component is 4 bits.<br/>
		A file ends with a (0, 0) tuple, that is, 18 zero bits.</p>

		<p>Uncompressing a LZSS-compressed file is quite easy, see lzss.py.</p>
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author	Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>
date	Fri, 17 Feb 2012 12:54:08 +0100
parents	b1bec4b5ccf3
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