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  1. #!/usr/bin/env python3
  2. from pprint import pprint as P
  3. import struct
  4.  
  5. def test(data_in, data_out):
  6.     print("==========================")
  7.     print("IN: %s"%data_in)
  8.     try:
  9.         r = decode(data_in)
  10.     except:
  11.         print("ERR: exception during decoding")
  12.     else:
  13.         print("FINAL OUT: %s"%r)
  14.         if r == data_out:
  15.             print("MATCH")
  16.         else:
  17.             print("ERR: decompressed output doesnt match %d %d"%(len(r), len(data_out)))
  18.  
  19. def main():
  20.  
  21.     test(bytes.fromhex(" ff ff ff 1f 61 62 63 17 00 0f ff 26 01"),
  22.          b'abcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabc'+
  23.          b'abcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabc'+
  24.          b'abcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabc'+
  25.          b'abcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabc'+
  26.          b'abcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabc')
  27.  
  28.     test(bytes.fromhex('ff ff ff 7f ff 07 00 0f ff 00 00 fc ff 01 00'),
  29.          b'\xff'*(1024*128))
  30.  
  31. def decode(ibuf):
  32.     obuf = bytearray()
  33.     BufferedFlags = 0
  34.     BufferedFlagCount = 0
  35.     InputPosition = 0
  36.     OutputPosition = 0
  37.     LastLengthHalfByte = 0
  38.  
  39.     def output(x):
  40.         obuf.append(x)
  41.         #print("OUT: %02x"%x)
  42.  
  43.     while True:
  44.         if BufferedFlagCount == 0:
  45.             # Read 4 bytes at InputPosition
  46.             BufferedFlags = struct.unpack_from('<I', ibuf, InputPosition)[0] 
  47.             InputPosition += 4
  48.             BufferedFlagCount = 32
  49.         BufferedFlagCount = BufferedFlagCount - 1
  50.         if (BufferedFlags & (1 << BufferedFlagCount)) == 0:
  51.             # Copy 1 byte from InputPosition to OutputPosition.  Advance both.
  52.             output(ibuf[InputPosition])
  53.             InputPosition += 1
  54.             OutputPosition += 1
  55.         else:
  56.             if InputPosition == len(ibuf):
  57.                 # Decompression is complete.  Return with success.
  58.                 return obuf
  59.             # Read 2 bytes from InputPosition
  60.             MatchBytes = struct.unpack_from('<H', ibuf, InputPosition)[0]
  61.             InputPosition += 2
  62.             MatchLength = MatchBytes % 8
  63.             MatchOffset = (MatchBytes // 8) + 1
  64.             if MatchLength == 7:
  65.                 if LastLengthHalfByte == 0:
  66.                     #read 1 byte from InputPosition
  67.                     MatchLength = ibuf[InputPosition]
  68.                     MatchLength = MatchLength % 16
  69.                     LastLengthHalfByte = InputPosition
  70.                     InputPosition += 1
  71.                 else:
  72.                     # read 1 byte from LastLengthHalfByte position
  73.                     MatchLength = ibuf[LastLengthHalfByte]
  74.                     MatchLength = MatchLength / 16
  75.                     LastLengthHalfByte = 0
  76.                 if MatchLength == 15:
  77.                     # read 1 byte from InputPosition
  78.                     MatchLength = ibuf[InputPosition]
  79.                     InputPosition += 1
  80.                     if MatchLength == 255:
  81.                         # read 2 bytes from InputPosition
  82.                         MatchLength = struct.unpack_from('<H', ibuf, InputPosition)[0]
  83.                         InputPosition += 2
  84.                         if MatchLength < 15 + 7:
  85.                            raise Exception("error")
  86.                         MatchLength -= (15 + 7)
  87.                     MatchLength += 15
  88.                 MatchLength += 7
  89.             MatchLength += 3
  90.             for i in range(MatchLength):# i = 0 to MatchLength - 1:
  91.                 # Copy 1 byte from OutputBuffer[OutputPosition - MatchOffset]
  92.                 output(obuf[OutputPosition-MatchOffset])
  93.                 OutputPosition += 1
  94.  
  95. if __name__ == '__main__':
  96.     main()
  97.  
Success #stdin #stdout 0.02s 27968KB
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stdin
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Standard input is empty
stdout
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==========================
IN: b'\xff\xff\xff\x1fabc\x17\x00\x0f\xff&\x01'
FINAL OUT: bytearray(b'abcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabcabc')
MATCH
==========================
IN: b'\xff\xff\xff\x7f\xff\x07\x00\x0f\xff\x00\x00\xfc\xff\x01\x00'
ERR: exception during decoding
https://ideone.com/7Lr6tN
language:
Python 3 (python  3.9.5)
created:
4 years ago
visibility:
public

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