Mercurial > touhou
comparison 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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| -1:000000000000 | 0:6b2c7af2384c |
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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 |