| # base85.py: pure python base85 codec |
| # |
| # Copyright (C) 2009 Brendan Cully <brendan@kublai.com> |
| # |
| # This software may be used and distributed according to the terms of the |
| # GNU General Public License version 2 or any later version. |
| |
| import struct |
| |
| _b85chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ" \ |
| "abcdefghijklmnopqrstuvwxyz!#$%&()*+-;<=>?@^_`{|}~" |
| _b85chars2 = [(a + b) for a in _b85chars for b in _b85chars] |
| _b85dec = {} |
| |
| def _mkb85dec(): |
| for i, c in enumerate(_b85chars): |
| _b85dec[c] = i |
| |
| 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) |
| |
| out = ''.join(_b85chars[(word // 52200625) % 85] + |
| _b85chars2[(word // 7225) % 7225] + |
| _b85chars2[word % 7225] |
| for word in words) |
| |
| if pad: |
| return out |
| |
| # Trim padding |
| olen = l % 4 |
| if olen: |
| olen += 1 |
| olen += l // 4 * 5 |
| 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 |
| for j, c in enumerate(chunk): |
| try: |
| acc = acc * 85 + _b85dec[c] |
| except KeyError: |
| raise ValueError('bad base85 character at position %d' |
| % (i + j)) |
| if acc > 4294967295: |
| raise ValueError('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 |
