blob: 9c1279b641b54f37636b508d756cab6934e94bb5 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
|
#!/usr/bin/python3
"""Print the codes in the first Huffman tree header in the given file.
USAGE: decode-huffman-header FILE
The number of codes of different length is printed first, followed by
the implied total frequency of codes, followed by the deduced codes.
If the total is not 1.0, the header is invalid.
"""
import sys
if '--help' in sys.argv or '-h' in sys.argv or len(sys.argv) != 2:
print(__doc__)
exit(len(sys.argv) != 2)
def read_table(data):
lengths = [[] for x in range(16)]
for i, b in enumerate(data):
even = b & 15
odd = b >> 4
lengths[even].append(i * 2)
lengths[odd].append(i * 2 + 1)
code = 0
total = 0.0
for i, bucket in enumerate(lengths):
if bucket and i:
portion = 1.0 / (1 << i) * len(bucket)
total += portion
print(f"length {i:2}: {len(bucket):4} ({portion})")
print(f"total {total}")
for i, bucket in enumerate(lengths):
if i == 0:
continue
code <<= 1
for c in bucket:
print(f'{c:03x} {code:0{i}b}')
code += 1
def main():
fn = sys.argv[1]
with open(fn, 'rb') as f:
data = f.read(256)
read_table(data)
main()
|
