base91.py

# Base91 encode/decode for Python 2 and Python 3
#
# Copyright (c) 2012 Adrien Beraud
# Copyright (c) 2015 Guillaume Jacquenot
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
#
#   * Redistributions of source code must retain the above copyright notice,
#     this list of conditions and the following disclaimer.
#   * Redistributions in binary form must reproduce the above copyright notice,
#     this list of conditions and the following disclaimer in the documentation
#     and/or other materials provided with the distribution.
#   * Neither the name of Adrien Beraud, Wisdom Vibes Pte. Ltd., nor the names
#     of its contributors may be used to endorse or promote products derived
#     from this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
# SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#
import struct

base91_alphabet = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
	'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
	'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm',
	'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z',
	'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '!', '#', '$',
	'%', '&', '(', ')', '*', '+', ',', '.', '/', ':', ';', '<', '=',
	'>', '?', '@', '[', ']', '^', '_', '`', '{', '|', '}', '~', '"']

decode_table = dict((v,k) for k,v in enumerate(base91_alphabet))

def decode(encoded_str):
    ''' Decode Base91 string to a bytearray '''
    v = -1
    b = 0
    n = 0
    out = bytearray()
    for strletter in encoded_str:
        if not strletter in decode_table:
            continue
        c = decode_table[strletter]
        if(v < 0):
            v = c
        else:
            v += c*91
            b |= v << n
            n += 13 if (v & 8191)>88 else 14
            while True:
                out += struct.pack('B', b&255)
                b >>= 8
                n -= 8
                if not n>7:
                    break
            v = -1
    if v+1:
        out += struct.pack('B', (b | v << n) & 255 )
    return out

def encode(bindata):
    ''' Encode a bytearray to a Base91 string '''
    b = 0
    n = 0
    out = ''
    for count in range(len(bindata)):
        byte = bindata[count:count+1]
        b |= struct.unpack('B', byte)[0] << n
        n += 8
        if n>13:
            v = b & 8191
            if v > 88:
                b >>= 13
                n -= 13
            else:
                v = b & 16383
                b >>= 14
                n -= 14
            out += base91_alphabet[v % 91] + base91_alphabet[v // 91]
    if n:
        out += base91_alphabet[b % 91]
        if n>7 or b>90:
            out += base91_alphabet[b // 91]
    return out