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view doc/PBG3 @ 0:6b2c7af2384c
Hello Gensokyo _o/
author | Thibaut Girka <thib@sitedethib.com> |
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date | Sun, 31 Jul 2011 21:32:12 +0200 |
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The PBG3 format is an archive format used by Touhou 6 (The Embodiment of Scarlet Devil). It is a bitstream composed of a header, a file table, and LZSS-compressed files. Reading integers ---------------- Integers in PBG3 files are never signed, they are not byte-aligned, and have a variable size. Their size is given by two bits: 00 means the number is stored in one byte, 10 means it is stored in three bytes. Ex: 0x0012 is stored as: 0000010010 0x0112 is stored as: 010000000100010010 Reading strings --------------- Strings are stored as standard NULL-terminated sequences of bytes. The only catch is they are not byte-aligned. Header ------ The header is composed of three fields: * magic (string): "PBG3" * number of entries (integer) * offset of the file table (integer) The size of the header is thus comprised between 52 bits and 100 bits. File table ---------- The file table starts at a byte boundary, but as the rest of the file, isn't byte-aligned. It consists of a sequence of entries. Each entry is composed of five fields: * unknown1 (int) #TODO * unknown2 (int) #TODO * checksum (int): simple checksum of compressed data * size (int): size of uncompressed data * name (string): name of the file The checksum is a mere sum of the compressed data. Files are compressed using the LZSS algorithm, with a dictionary size of 8192 bytes and a minimum matching length of 4 bytes. The size of the offset component of (offset, length) tuples is 13 bits, whereas the size of the length component is 4 bits. A file ends with a (0, 0) tuple, that is, 18 zero bits. Uncompressing a LZSS-compressed file is quite easy, see lzss.py.