base85.py
74 lines
| 1.9 KiB
| text/x-python
|
PythonLexer
|
r7701 | # base85.py: pure python base85 codec | ||
# | ||||
# Copyright (C) 2009 Brendan Cully <brendan@kublai.com> | ||||
# | ||||
|
r8225 | # This software may be used and distributed according to the terms of the | ||
|
r10263 | # GNU General Public License version 2 or any later version. | ||
|
r7701 | |||
import struct | ||||
_b85chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ" \ | ||||
"abcdefghijklmnopqrstuvwxyz!#$%&()*+-;<=>?@^_`{|}~" | ||||
|
r7835 | _b85chars2 = [(a + b) for a in _b85chars for b in _b85chars] | ||
|
r7701 | _b85dec = {} | ||
def _mkb85dec(): | ||||
|
r8632 | for i, c in enumerate(_b85chars): | ||
_b85dec[c] = i | ||||
|
r7701 | |||
def b85encode(text, pad=False): | ||||
"""encode text in base85 format""" | ||||
l = len(text) | ||||
r = l % 4 | ||||
if r: | ||||
text += '\0' * (4 - r) | ||||
longs = len(text) >> 2 | ||||
words = struct.unpack('>%dL' % (longs), text) | ||||
|
r9029 | out = ''.join(_b85chars[(word // 52200625) % 85] + | ||
_b85chars2[(word // 7225) % 7225] + | ||||
|
r7835 | _b85chars2[word % 7225] | ||
for word in words) | ||||
|
r7701 | |||
if pad: | ||||
return out | ||||
# Trim padding | ||||
olen = l % 4 | ||||
if olen: | ||||
olen += 1 | ||||
|
r9029 | olen += l // 4 * 5 | ||
|
r7701 | return out[:olen] | ||
def b85decode(text): | ||||
"""decode base85-encoded text""" | ||||
if not _b85dec: | ||||
_mkb85dec() | ||||
l = len(text) | ||||
out = [] | ||||
for i in range(0, len(text), 5): | ||||
chunk = text[i:i+5] | ||||
acc = 0 | ||||
|
r8632 | for j, c in enumerate(chunk): | ||
|
r7701 | try: | ||
|
r8632 | acc = acc * 85 + _b85dec[c] | ||
|
r7701 | except KeyError: | ||
raise TypeError('Bad base85 character at byte %d' % (i + j)) | ||||
if acc > 4294967295: | ||||
raise OverflowError('Base85 overflow in hunk starting at byte %d' % i) | ||||
out.append(acc) | ||||
# Pad final chunk if necessary | ||||
cl = l % 5 | ||||
if cl: | ||||
acc *= 85 ** (5 - cl) | ||||
if cl > 1: | ||||
acc += 0xffffff >> (cl - 2) * 8 | ||||
out[-1] = acc | ||||
out = struct.pack('>%dL' % (len(out)), *out) | ||||
if cl: | ||||
out = out[:-(5 - cl)] | ||||
return out | ||||