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import sys
class Stream:
def __init__(self, string):
self.string = string
self.cursor = 0
def read_elias(self):
offset = self.cursor
if self.string[0 + offset] == "1":
self.cursor += 1
return 1
start, end = 1, 2
while True:
binary = self.string[start + offset:end + 1 + offset]
if binary[0] == "0":
chunk = int(f"1{binary[1:]}", 2) + 1
start = end + 1
end += chunk
else:
self.cursor += end + 1
return int(binary, 2)
def read_binary(self, length):
blob = self.string[self.cursor:self.cursor + length]
self.cursor += length
return blob
def read_int(self, bits):
return int(self.read_binary(bits), 2)
def read_char(self, bits=7):
return chr(self.read_int(bits))
def read_bit(self):
return self.read_binary(1)
def read_huff_char(self, decode_table):
window_size = 1
window = self.string[self.cursor:self.cursor + window_size]
while window not in decode_table:
if window_size >= len(self.string):
raise Exception("Went for too long looking for a Huffman char")
window_size += 1
window = self.string[self.cursor:self.cursor + window_size]
self.cursor += window_size
return decode_table[window]
def read_lzss_tuple(self, decode_table):
format_type = self.read_bit()
if format_type == "0":
return 0, self.read_elias(), self.read_elias()
else:
return 1, self.read_huff_char(decode_table)
def parse_header(stream):
huff = {}
alphabet_size = stream.read_elias()
for i in range(alphabet_size):
char = stream.read_char()
length = stream.read_elias()
codeword = stream.read_binary(length)
huff[codeword] = char
return huff
def parse_body_tuples(stream, decode_table):
num_tuples = stream.read_elias()
return [stream.read_lzss_tuple(decode_table) for _ in range(num_tuples)]
def decode_lzss(tuples):
result = ""
for tup in tuples:
if tup[0] == 0:
_, offset, length = tup
cursor = len(result) - offset
for i in map(lambda x: x % offset, range(length)):
result += result[cursor + i]
else:
result += tup[1]
return result
def decode_message(raw_data):
stream = Stream(raw_data)
decode_table = parse_header(stream)
tuples = parse_body_tuples(stream, decode_table)
return decode_lzss(tuples)
def read_file(filename):
with open(filename, "r") as file:
contents = file.read()
return contents
def write_file(filename, contents):
with open(filename, "w") as file:
file.write(contents)
def main():
assert len(sys.argv) >= 2
raw = read_file(sys.argv[1])
result = decode_message(raw)
write_file("output_decoder_lzss.txt", result)
if __name__ == "__main__":
main()
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