def encode(bindata):
    ''' Encode a bytearray to a Base91 string '''
    l = len(bindata)
    b = 0
    n = 0
    out = ''
    for byte in bindata:
        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