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1 class BitStream(object):
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2 def __init__(self, io):
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3 self.io = io
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4 self.bits = 0
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5 self.byte = 0
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6
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7
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8 def seek(self, offset, whence=0):
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9 self.io.seek(offset, whence)
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10 self.byte = 0
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11 self.bits = 0
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12
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13
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14 def tell(self):
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15 return self.io.tell()
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16
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17
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18 def tell2(self):
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19 return self.io.tell(), self.bits
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20
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21
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22 def read_bit(self):
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23 if not self.bits:
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24 self.byte = ord(self.io.read(1))
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25 self.bits = 8
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26 self.bits -= 1
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27 return (self.byte >> self.bits) & 0x01
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28
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29
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30 def read(self, nb_bits):
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31 value = 0
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32 for i in range(nb_bits - 1, -1, -1):
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33 value |= self.read_bit() << i
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34 return value
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35
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36
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37 def write_bit(self, bit):
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38 if self.bits == 8:
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39 self.io.write(chr(self.byte))
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40 self.bits = 0
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41 self.byte = 0
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42 self.byte &= ~(1 << (7 - self.bits))
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43 self.byte |= bit << (7 - self.bits)
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44 self.bits += 1
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45
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46
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47 def write(self, bits, nb_bits):
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48 for i in range(nb_bits):
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49 self.write_bit(bits >> (nb_bits - 1 - i) & 0x01)
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50
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51
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52 def flush(self):
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53 self.io.write(chr(self.byte))
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54 self.bits = 0
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55 self.byte = 0
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56 self.io.flush()
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57
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