Mercurial > touhou
comparison pytouhou/utils/lzss.py @ 0:6b2c7af2384c
Hello Gensokyo _o/
| author | Thibaut Girka <thib@sitedethib.com> |
|---|---|
| date | Sun, 31 Jul 2011 21:32:12 +0200 |
| parents | |
| children | ab826bc29aa2 |
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| -1:000000000000 | 0:6b2c7af2384c |
|---|---|
| 1 def decompress(bitstream, size, dictionary_size=0x2000, | |
| 2 offset_size=13, length_size=4, minimum_match_length=3): | |
| 3 out_data = [] | |
| 4 dictionary = [0] * dictionary_size | |
| 5 dictionary_head = 1 | |
| 6 while len(out_data) < size: | |
| 7 flag = bitstream.read_bit() | |
| 8 if flag: | |
| 9 # The `flag` bit is set, indicating the upcoming chunk of data is a literal | |
| 10 # Add it to the uncompressed file, and store it in the dictionary | |
| 11 byte = bitstream.read(8) | |
| 12 dictionary[dictionary_head] = byte | |
| 13 dictionary_head = (dictionary_head + 1) % dictionary_size | |
| 14 out_data.append(byte) | |
| 15 else: | |
| 16 # The `flag` bit is not set, the upcoming chunk is a (offset, length) tuple | |
| 17 offset = bitstream.read(offset_size) | |
| 18 length = bitstream.read(length_size) + minimum_match_length | |
| 19 if (offset, length) == (0, 0): | |
| 20 break | |
| 21 for i in range(offset, offset + length): | |
| 22 out_data.append(dictionary[i % dictionary_size]) | |
| 23 dictionary[dictionary_head] = dictionary[i % dictionary_size] | |
| 24 dictionary_head = (dictionary_head + 1) % dictionary_size | |
| 25 return b''.join(chr(byte) for byte in out_data) |