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