def encode(self, message):
#initializing Table[0 to 255] to corresponding ASCII charaters
Table = initialize(encode=True)
#initializing table index and P
index = 256
counter = 0
output = []
P = ''
#LZW compression algorithm
while counter != len(message) + 1:
try:
C = message[counter]
except IndexError: # for the last iteration, C is empty so just return P and exit
output.append(Table[P])
break
if P + C in Table:
P = P + C
else:
output.append(Table[P])
Table[P + C] = index
index += 1
P = C
counter += 1
#if the dictionary outgrew the word_size, re_initialize the dictionary
if index > 2**self.word_size:
Table = initialize(encode=True)
index = 256
packed_output = BitString()
packed_output.pack_numbers(output, self.word_size)
return packed_output
def encode(self, message):
output = []
main_dictionary = {}
for i in range(256):
main_dictionary[chr(i)] = i
string = message[0]
curr_index = 0
l = len(message)
while curr_index < l - 1:
symbol = message[curr_index + 1]
if string + symbol in main_dictionary:
string += symbol
else:
output.append(main_dictionary[string])
max_key = max(main_dictionary, key=main_dictionary.get)
max_val = main_dictionary[max_key]
if max_val == 2**16 - 1:
main_dictionary = {}
for i in range(256):
main_dictionary[chr(i)] = i
#main_dictionary[string+symbol]=0
else:
main_dictionary[string + symbol] = max_val + 1
string = symbol
curr_index += 1
output.append(main_dictionary[string])
bits = BitString()
bits.pack_numbers(output, 16)
return bits
