[Python-Dev] Base-96 (original) (raw)

Josiah Carlson josiah.carlson at gmail.com
Sat Aug 2 19:37:34 CEST 2008

On Sat, Aug 2, 2008 at 10:09 AM, "Martin v. Löwis" <martin at v.loewis.de> wrote:

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.

Original intent (encoding IPV6 addresses) != current usefulness (a more efficient ascii encoding of binary data). Generally, I'm of the opinion that base64 (as an ascii encoding of binary data) is sufficient for any needs I have, but there are cases where having a more efficient representation would be useful. I would also not suggest addition in the 2.6/3.0 timeframe, at best it would be 2.7/3.1, and only if someone submits a patch with testcases (note that the wiki page provides C source for one-shot encoding and decoding that doesn't require 128-bit arithmetic).

Sounds to me like a project for the OP.

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