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import sys
def main():
input_file = sys.argv[1]
output_file = sys.argv[2]
with open(input_file, 'rb') as f_in, open(output_file, 'wb') as f_out:
decompressed_length = int.from_bytes(f_in.read(4), 'little')
bytes_written = 0
output_buffer = [0] * 4096
output_buffer_pos = 0xFEE
def get_byte(offset):
nonlocal output_buffer
return output_buffer[offset % len(output_buffer)]
def write_byte(b):
nonlocal output_buffer, output_buffer_pos, bytes_written, f_out
output_buffer[output_buffer_pos] = b
output_buffer_pos += 1
output_buffer_pos %= len(output_buffer)
bytes_written += 1
f_out.write(bytes([b]))
while True:
# >= to catch an over-run, if we're unlucky enough for one to
# happen
if bytes_written >= decompressed_length:
return
control = ord(f_in.read(1))
control_bits = [(control >> i) & 1 for i in range(8)]
for control_bit in control_bits:
# same deal as above
if bytes_written >= decompressed_length:
return
if control_bit == 1:
# literal
literal = ord(f_in.read(1))
write_byte(literal)
else:
# reference
reference = int.from_bytes(f_in.read(2), 'big')
offset = (((reference >> 4) & 0xF) << 8) | (reference >> 8)
length = (reference & 0xF) + 3
for i in range(length):
write_byte(get_byte(offset + i))
if __name__ == '__main__':
main()
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