104 lines
2.4 KiB
Python
104 lines
2.4 KiB
Python
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"""
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This module contains generic base85 encoding and decoding functions. The
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whoosh.util.numeric module contains faster variants for encoding and
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decoding integers.
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Modified from:
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http://paste.lisp.org/display/72815
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"""
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import struct
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from whoosh.compat import xrange
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# Instead of using the character set from the ascii85 algorithm, I put the
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# characters in order so that the encoded text sorts properly (my life would be
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# a lot easier if they had just done that from the start)
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b85chars = ("!$%&*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ"
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"^_abcdefghijklmnopqrstuvwxyz{|}~")
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b85dec = {}
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for i in range(len(b85chars)):
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b85dec[b85chars[i]] = i
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# Integer encoding and decoding functions
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def to_base85(x, islong=False):
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"Encodes the given integer using base 85."
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size = 10 if islong else 5
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rems = ""
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for i in xrange(size):
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rems = b85chars[x % 85] + rems
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x //= 85
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return rems
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def from_base85(text):
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"Decodes the given base 85 text into an integer."
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acc = 0
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for c in text:
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acc = acc * 85 + b85dec[c]
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return acc
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# Bytes encoding and decoding functions
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def b85encode(text, pad=False):
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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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out = []
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words = struct.unpack('>' + 'L' * longs, text[0:longs * 4])
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for word in words:
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rems = [0, 0, 0, 0, 0]
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for i in range(4, -1, -1):
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rems[i] = b85chars[word % 85]
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word /= 85
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out.extend(rems)
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out = ''.join(out)
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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[0:olen]
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def b85decode(text):
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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 in range(len(chunk)):
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try:
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acc = acc * 85 + b85dec[chunk[j]]
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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('>' + 'L' * ((l + 4) / 5), *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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