base 64

    A file format using 64 ASCII
   characters to encode the six bit binary data values 0-63.

   To convert data to base 64, the first byte is placed in the
   most significant eight bits of a 24-bit buffer, the next in
   the middle eight, and the third in the least significant eight
   bits.  If there a fewer than three bytes to encode, the
   corresponding buffer bits will be zero.  The buffer is then
   used, six bits at a time, most significant first, as indices
   into the string
   "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
   and the indicated character output.  If there were only one or
   two input bytes, the output is padded with two or one "="
   characters respectively.  This prevents extra bits being added
   to the reconstructed data.  The process then repeats on the
   remaining input data.

   Base 64 is used when transmitting binary data through
   text-only media such as electronic mail, and has largely
   replaced the older uuencode encoding.

   (2004-07-17)