69 lines
1.6 KiB
Python
69 lines
1.6 KiB
Python
import sys
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def opts(byte):
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# top bit: 0 = left, 1 = right
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# bottom bit: 0 = or, 1 = and
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if byte is None: return []
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return [
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byte | (byte << 1) & 0xff,
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byte & (byte << 1),
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byte | (byte >> 1) & 0xff,
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byte & (byte >> 1),
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]
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def pb12(data):
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data = iter(data)
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literals = bytearray()
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bits = 0
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control = 0
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prev = [None, None]
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gotta_end = False
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chunk = bytearray()
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while True:
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try:
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byte = next(data)
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except StopIteration:
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if bits == 0: break
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byte = 0
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chunk.append(byte)
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if byte in prev:
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bits += 2
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control <<= 1
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control |= 1
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control <<= 1
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if prev[1] == byte:
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control |= 1 # 10 = out[-2], 11 = out[-1]
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else:
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bits += 2
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control <<= 2
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options = opts(prev[1])
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if byte in options:
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# 01 = modify
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control |= 1
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bits += 2
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control <<= 2
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control |= options.index(byte)
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else:
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# 00 = literal
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literals.append(byte)
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prev = [prev[1], byte]
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if bits >= 8:
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outctl = control >> (bits - 8)
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assert outctl != 1 # that's the end byte
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yield bytes([outctl]) + literals
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bits -= 8
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control &= (1 << bits) - 1
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literals = bytearray()
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chunk = bytearray()
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yield b'\x01'
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_, infile, outfile = sys.argv
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with open(infile, 'rb') as f:
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data = f.read()
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with open(outfile, 'wb') as f:
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f.writelines(pb12(data))
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