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