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+ − 1 The PBG3 format is an archive format used by Touhou 6 (The Embodiment of Scarlet Devil).
+ − 2
+ − 3 It is a bitstream composed of a header, a file table, and LZSS-compressed files.
+ − 4
+ − 5
+ − 6
+ − 7 Reading integers
+ − 8 ----------------
+ − 9
+ − 10 Integers in PBG3 files are never signed, they are not byte-aligned, and have a variable size.
+ − 11 Their size is given by two bits: 00 means the number is stored in one byte, 10 means it is stored in three bytes.
+ − 12
+ − 13 Ex:
+ − 14 0x0012 is stored as: 0000010010
+ − 15 0x0112 is stored as: 010000000100010010
+ − 16
+ − 17
+ − 18
+ − 19 Reading strings
+ − 20 ---------------
+ − 21
+ − 22 Strings are stored as standard NULL-terminated sequences of bytes.
+ − 23 The only catch is they are not byte-aligned.
+ − 24
+ − 25
+ − 26
+ − 27 Header
+ − 28 ------
+ − 29
+ − 30 The header is composed of three fields:
+ − 31 * magic (string): "PBG3"
+ − 32 * number of entries (integer)
+ − 33 * offset of the file table (integer)
+ − 34
+ − 35 The size of the header is thus comprised between 52 bits and 100 bits.
+ − 36
+ − 37
+ − 38
+ − 39 File table
+ − 40 ----------
+ − 41
+ − 42 The file table starts at a byte boundary, but as the rest of the file, isn't byte-aligned.
+ − 43 It consists of a sequence of entries.
+ − 44 Each entry is composed of five fields:
+ − 45 * unknown1 (int) #TODO
+ − 46 * unknown2 (int) #TODO
+ − 47 * checksum (int): simple checksum of compressed data
+ − 48 * size (int): size of uncompressed data
+ − 49 * name (string): name of the file
+ − 50
+ − 51 The checksum is a mere sum of the compressed data.
+ − 52 Files are compressed using the LZSS algorithm, with a dictionary size of 8192 bytes and a minimum matching length of 4 bytes.
+ − 53 The size of the offset component of (offset, length) tuples is 13 bits, whereas the size of the length component is 4 bits.
+ − 54 A file ends with a (0, 0) tuple, that is, 18 zero bits.
+ − 55
+ − 56 Uncompressing a LZSS-compressed file is quite easy, see lzss.py.
+ − 57
