[Python-Dev] Base-96

["Martin v. Löwis"]

Josiah Carlson wrote:
> The standard high-bit-density encoding past base-64 is base-85
> (http://en.wikipedia.org/wiki/Ascii85), which encodes 4 binary bytes
> as 5 ascii bytes, versus 3 binary bytes as 4 ascii bytes.  It works,
> is an RFC somewhere,

RFC 1924, published on April 1, 1996, to shorten the representation
of IPv6 addresses, so that you can write

  ssh '4)+k&C#VzJ4br>0wv%Yp'

instead of having to write

  ssh 1080:0:0:0:8:800:200C:417A

Most notably, section 7 (implementation issues) points out

   Many current processors do not find 128 bit integer arithmetic, as
   required for this technique, a trivial operation.  This is not
   considered a serious drawback in the representation, but a flaw of
   the processor designs.

For arbitrary-sized data, you'd have to give up 128-bit arithmetic,
of course, and represent the input data to encode as a long integer.

Regards,
Martin

P.S. Just in case it isn't clear: I would oppose any specific proposal
to add this Ascii85 algorithm to the standard library. It would sound
like we don't have any real problems to solve.