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annotate pytouhou/utils/lzss.py @ 204:88361534c77e

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Add some documentation (argh, so much left to document!)
author Thibaut Girka <thib@sitedethib.com>
date Tue, 01 Nov 2011 13:46:03 +0100
parents ab826bc29aa2
children
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ab826bc29aa2 Add some documentation, GPLv3 headers, README and COPYING file.
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1 # -*- encoding: utf-8 -*-
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2 ##
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3 ## Copyright (C) 2011 Thibaut Girka <thib@sitedethib.com>
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4 ##
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5 ## This program is free software; you can redistribute it and/or modify
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6 ## it under the terms of the GNU General Public License as published
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7 ## by the Free Software Foundation; version 3 only.
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8 ##
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9 ## This program is distributed in the hope that it will be useful,
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10 ## but WITHOUT ANY WARRANTY; without even the implied warranty of
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11 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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12 ## GNU General Public License for more details.
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13 ##
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14
0
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15 def decompress(bitstream, size, dictionary_size=0x2000,
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16 offset_size=13, length_size=4, minimum_match_length=3):
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17 out_data = []
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18 dictionary = [0] * dictionary_size
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19 dictionary_head = 1
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20 while len(out_data) < size:
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21 flag = bitstream.read_bit()
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22 if flag:
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23 # The `flag` bit is set, indicating the upcoming chunk of data is a literal
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24 # Add it to the uncompressed file, and store it in the dictionary
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25 byte = bitstream.read(8)
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26 dictionary[dictionary_head] = byte
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27 dictionary_head = (dictionary_head + 1) % dictionary_size
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28 out_data.append(byte)
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29 else:
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30 # The `flag` bit is not set, the upcoming chunk is a (offset, length) tuple
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31 offset = bitstream.read(offset_size)
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32 length = bitstream.read(length_size) + minimum_match_length
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33 if (offset, length) == (0, 0):
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34 break
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35 for i in range(offset, offset + length):
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36 out_data.append(dictionary[i % dictionary_size])
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37 dictionary[dictionary_head] = dictionary[i % dictionary_size]
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38 dictionary_head = (dictionary_head + 1) % dictionary_size
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39 return b''.join(chr(byte) for byte in out_data)