def decompress(compf, f):
"""
Decompress a file.
"""
# read alphabet
alphabet = cPickle.load(compf)
print "alphabet:\n%r" % alphabet
count = 0
while True:
header = compf.read(8)
if header == '':
break
print "block %r:" % count
nbits, I = struct.unpack('>2I', header)
freqs = load_freqs(compf)
#print freqs
nbyte = (nbits+7) / 8
huff_encode = to01(compf.read(nbyte))[:nbits]
#print "huff_encode:\n%r" % huff_encode
coding, root = huff.generate_coding(freqs)
#print "coding:\n%r" % coding
huff_decode = huff.decode(huff_encode, root)
mtf_decode = mtf.decode(alphabet, huff_decode)
bwt_decode = bwt.decode(mtf_decode, I, reverse = True)
content = ''.join(bwt_decode)
f.write(content)
print "nbits = %r, I = %r, length = %r" % (nbits, I, len(content))
count = count + 1
def test_same(self):
seq = [0] * 16
from collections import Counter
freqs = Counter(seq)
coding, root = huff.generate_coding(freqs)
encode = huff.encode(seq, coding)
decode = huff.decode("".join(encode), root)
self.assertEqual(list(seq), decode)
def test_mix(self):
seq = [1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 3, 4, 4, 4, 5, 5, 5]
random.shuffle(seq)
from collections import Counter
freqs = Counter(seq)
expect = {1: "10", 2: "01", 3: "11", 4: "001", 5: "000"}
coding, root = huff.generate_coding(freqs)
self.assertDictEqual(expect, coding)
encode = huff.encode(seq, coding)
decode = huff.decode("".join(encode), root)
self.assertEqual(seq, decode)
def compress(f, compf, block = None):
"""
Compress a file by bwt-mtf-huff processes.
f: a file-like object, content for compressing
compf: compression result
"""
# craete alphabet for move-to-front
content = f.read()
alphabet_set = set(content)
alphabet = [''] + list(alphabet_set)
# dump alphabet
cPickle.dump(alphabet, compf, 2)
content = None
f.seek(0)
count = 0
while True:
data = f.read(BLOCK_SIZE)
if data == '':
break
if block == None or block == count:
print "block %r:" % count
bwt_encode, I = bwt.encode(data)
mtf_encode = mtf.encode(alphabet, bwt_encode)
# create Huffman tree
freqs = Counter(mtf_encode)
if block:
print freqs
coding, root = huff.generate_coding(freqs)
if block:
print coding
# encoding
huff_encode = ''.join(huff.encode(mtf_encode, coding))
#print "huff_encode:\n%r" % huff_encode
nbits = len(huff_encode)
huff_bytes = tobytes(huff_encode)
compf.write(struct.pack(">2I", nbits, I))
dump_freqs(compf, freqs)
compf.write(huff_bytes)
print "nbits = %r, I = %r, length = %r" % (nbits, I, len(data))
count = count + 1
