[Python-Dev] Re: PEP239 (Rational Numbers) Reference Implementation and new issues

[Christopher A. Craig]

Tim Peters <tim.one@comcast.net> writes:

> If you haven't yet, you should strive to understand Moshe Zadka's prototype
> rational implementation in Python CVS nondist/sandbox/ (which has all the
> approximation functions you could need).  Unfortunately, the SourceForge
> Python Numerics list:
> 
>     https://sourceforge.net/mailarchive/forum.php?forum_id=2280
> 
> appears to have lost almost all the voluminous discussions that went into
> that, retaining mostly a random sampling of spam.

I have read the module.  I really liked his (your?) trim code and I
used that algorithm in cRat and my rational patch.  I don't think I'd
use any of that for generating decimal (or binary) float
approximations, though.  Trim introduces some error into the
calculation which is then furthered by the float division.  You can
provably generate the closest scaled long of a given size (and thus
hopefully the closest float) with one shift and one long integer
division.

-- 
Christopher A. Craig <list-python@ccraig.org>
"It mearly pleases me to behave in a certain way to what appears to be a
cat" -- The Ruler of the Universe (The Restaurant at the End of the Universe)