LZ78Decoder.py

from base64 import decode
from symtable import Symbol
import time

from LZ78Coder import LZ78_file


filenames = ["cantrbry/kennedy.xls"] #, "cantrbry/fields.c", "cantrbry/sum"]

shortfilenames = ["cantrbry/alice29.txt", "cantrbry/asyoulik.txt", "cantrbry/cp.html", "cantrbry/fields.c", "cantrbry/grammar.lsp", "cantrbry/kennedy.xls", "cantrbry/lcet10.txt",
                  "cantrbry/plrabn12.txt", "cantrbry/ptt5", "cantrbry/sum", "cantrbry/xargs.1"]
bigfilenames = ["large/bible.txt", "large/E.coli", "large/world192.txt"]

BITS = 10

def read_file(filename):
    # Load bytes from file and count symbol occurances
    with open(filename, "rb") as f:  # 'rb' means read binary
        data = f.read()
        return data


def LZ78_decoder(filename, code):
    datasize = len(code)
    decoded = []
    i = 0
    while i <= len(code)-1:
        index_symbol = code[i]
        if index_symbol[0] == 0 or index_symbol[0] == 2**BITS-1:
            if index_symbol[1] != None :  # not None
                decoded.append(index_symbol[1])
                i += 1
            elif index_symbol[0] == 2**BITS-1:   # clear code and start over
                code = code[i+1:]
                i = 0
                print(f'dec {filename} @ {len(decoded)}')
            elif index_symbol[1] == None:  
                i += 1

        else:
            symbols = [index_symbol[1]]
            next_index_symbol = code[index_symbol[0]]
            while next_index_symbol[0] != 0:
                symbols.insert(0, next_index_symbol[1])
                next_index_symbol = code[next_index_symbol[0]]
            symbols.insert(0, next_index_symbol[1])

            # add symbols to decoded
            for symbol in symbols:
                decoded.append(symbol)

            i += 1

    return decoded


for filename in bigfilenames:

    # Coding
    start = time.time()
    list = [(0, None)]
    code = LZ78_file(filename, list)
    end = time.time()

    print("Coding ", filename, " took ", end-start, " seconds!\n")

    # Decoding
    tic = time.time()
    decoded = LZ78_decoder(filename, code)
    tec = time.time()

    #%%
    nr_symbols = 500
    print(f'\nFirst {nr_symbols} symbols is:\n\n')
    
    for i in range(0, nr_symbols):
        print(chr(decoded[i]), end="")
        
    #%%
    #for i in range(len(orig)):
    #    if(orig[i] != decoded[i]):
    #        print(decoded[i])

    print("\n\nDecoding took ", tec-tic, " seconds")