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1 | 1 | # base85.py: pure python base85 codec |
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2 | 2 | # |
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3 | 3 | # Copyright (C) 2009 Brendan Cully <brendan@kublai.com> |
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4 | 4 | # |
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5 | 5 | # This software may be used and distributed according to the terms of |
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6 | 6 | # the GNU General Public License, incorporated herein by reference. |
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7 | 7 | |
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8 | 8 | import struct |
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9 | 9 | |
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10 | 10 | _b85chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ" \ |
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11 | 11 | "abcdefghijklmnopqrstuvwxyz!#$%&()*+-;<=>?@^_`{|}~" |
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12 | _b85chars2 = [(a + b) for a in _b85chars for b in _b85chars] | |
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12 | 13 | _b85dec = {} |
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13 | 14 | |
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14 | 15 | def _mkb85dec(): |
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15 | 16 | for i in range(len(_b85chars)): |
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16 | 17 | _b85dec[_b85chars[i]] = i |
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17 | 18 | |
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18 | 19 | def b85encode(text, pad=False): |
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19 | 20 | """encode text in base85 format""" |
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20 | 21 | l = len(text) |
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21 | 22 | r = l % 4 |
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22 | 23 | if r: |
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23 | 24 | text += '\0' * (4 - r) |
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24 | 25 | longs = len(text) >> 2 |
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25 | out = [] | |
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26 | 26 | words = struct.unpack('>%dL' % (longs), text) |
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27 | for word in words: | |
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28 | # unrolling improved speed by 33% | |
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29 | word, r = divmod(word, 85) | |
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30 | e = _b85chars[r] | |
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31 | word, r = divmod(word, 85) | |
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32 | d = _b85chars[r] | |
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33 | word, r = divmod(word, 85) | |
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34 | c = _b85chars[r] | |
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35 | word, r = divmod(word, 85) | |
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36 | b = _b85chars[r] | |
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37 | word, r = divmod(word, 85) | |
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38 | a = _b85chars[r] | |
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39 | 27 | |
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40 | out += (a, b, c, d, e) | |
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28 | out = ''.join(_b85chars[(word / 52200625) % 85] + | |
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29 | _b85chars2[(word / 7225) % 7225] + | |
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30 | _b85chars2[word % 7225] | |
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31 | for word in words) | |
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41 | 32 | |
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42 | out = ''.join(out) | |
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43 | 33 | if pad: |
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44 | 34 | return out |
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45 | 35 | |
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46 | 36 | # Trim padding |
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47 | 37 | olen = l % 4 |
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48 | 38 | if olen: |
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49 | 39 | olen += 1 |
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50 | 40 | olen += l / 4 * 5 |
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51 | 41 | return out[:olen] |
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52 | 42 | |
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53 | 43 | def b85decode(text): |
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54 | 44 | """decode base85-encoded text""" |
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55 | 45 | if not _b85dec: |
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56 | 46 | _mkb85dec() |
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57 | 47 | |
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58 | 48 | l = len(text) |
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59 | 49 | out = [] |
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60 | 50 | for i in range(0, len(text), 5): |
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61 | 51 | chunk = text[i:i+5] |
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62 | 52 | acc = 0 |
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63 | 53 | for j in range(len(chunk)): |
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64 | 54 | try: |
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65 | 55 | acc = acc * 85 + _b85dec[chunk[j]] |
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66 | 56 | except KeyError: |
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67 | 57 | raise TypeError('Bad base85 character at byte %d' % (i + j)) |
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68 | 58 | if acc > 4294967295: |
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69 | 59 | raise OverflowError('Base85 overflow in hunk starting at byte %d' % i) |
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70 | 60 | out.append(acc) |
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71 | 61 | |
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72 | 62 | # Pad final chunk if necessary |
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73 | 63 | cl = l % 5 |
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74 | 64 | if cl: |
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75 | 65 | acc *= 85 ** (5 - cl) |
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76 | 66 | if cl > 1: |
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77 | 67 | acc += 0xffffff >> (cl - 2) * 8 |
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78 | 68 | out[-1] = acc |
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79 | 69 | |
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80 | 70 | out = struct.pack('>%dL' % (len(out)), *out) |
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81 | 71 | if cl: |
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82 | 72 | out = out[:-(5 - cl)] |
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83 | 73 | |
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84 | 74 | return out |
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