def get_frequencies(filepath): freqs = arithmeticcoding.SimpleFrequencyTable([0] * 257) with open(filepath, "rb") as input: while True: b = input.read(1) if len(b) == 0: break b = b[0] if python3 else ord(b) freqs.increment(b) return freqs
def read_frequencies(bitin):
def read_int(n):
result = 0
for _ in range(n):
result = (result << 1) | bitin.read_no_eof() # Big endian
return result
freqs = [read_int(32) for _ in range(256)]
freqs.append(1) # EOF symbol
return arithmeticcoding.SimpleFrequencyTable(freqs)
def decompress(bitin, out):
initfreqs = arithmeticcoding.FlatFrequencyTable(257)
freqs = arithmeticcoding.SimpleFrequencyTable(initfreqs)
dec = arithmeticcoding.ArithmeticDecoder(32, bitin)
while True:
# Decode and write one byte
symbol = dec.read(freqs)
if symbol == 256: # EOF symbol
break
out.write(bytes((symbol, )))
freqs.increment(symbol)
def compress(inp, bitout):
initfreqs = arithmeticcoding.FlatFrequencyTable(257)
freqs = arithmeticcoding.SimpleFrequencyTable(initfreqs)
enc = arithmeticcoding.ArithmeticEncoder(32, bitout)
while True:
# Read and encode one byte
symbol = inp.read(1)
if len(symbol) == 0:
break
symbol = symbol[0] if python3 else ord(symbol)
enc.write(freqs, symbol)
freqs.increment(symbol)
enc.write(freqs, 256) # EOF
enc.finish() # Flush remaining code bits
def __init__(self, symbols, hassubctx):
self.frequencies = arithmeticcoding.SimpleFrequencyTable([0] *
symbols)
self.subcontexts = ([None] * symbols) if hassubctx else None