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