import sys class Stream: def __init__(self, string): self.string = string self.cursor = 0 def rewind(self): self.cursor = 0 def end_of_stream(self): return self.cursor >= len(self.string) 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 elias(n): assert n > 0 binary = bin(n)[2:] result = binary while len(binary) != 1: binary = "0" + bin(len(binary) - 1)[3:] result = binary + result return result def decode_elias(encoded, offset=0): if encoded[0 + offset] == "1": return 1 start, end = 1, 2 while True: binary = encoded[start + offset:end + 1 + offset] if binary[0] == "0": chunk = int(f"1{binary[1:]}", 2) + 1 start = end + 1 end += chunk else: return int(binary, 2) 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) print(decode_message("01111000011111000100100011000110100100011111111010011000100100001101111"))