[Python-numerics]Re: [Python-Dev] Re: WYSIWYG decimal fractions

[Tim Peters]

[Alex Martelli]
> ...
> There's another free library that interoperates with GMP to remedy
> this -- it's called MPFR and lives at http://www.loria.fr/projets/mpfr/.
> It's also LGPL.  I haven't looked much into it as it seems it's not been
> ported to Windows yet (and that looks like quite a project) which is
> the platform I'm currently using (and, rationals do what I need:-).

Thanks for the pointer!  From a quick skim, good news & bad news (although
which is which may depend on POV):

+ The authors apparently believe their MPFR routines "should replace
  the MPF class in further releases of GMP".  Then somebody else will
  port them.

+ Allows exact specification of result precision (which will make the
  results 100% platform-independent, unlike GMP's).

+ Allows choice of IEEE 754 rounding modes (unlike GMP's truncation).

+ But is still binary floating-point.

Marc-Andre is especially interested in decimal fixed- and floating-point, and
even more specifically than that, of a flavor that will be efficient for
working with decimal types in databases (which I suspect-- but don't
know --means that I/O (conversion) costs are more important than computation
speed once converted).  GMP + MPFR don't really address the decimal part of
that.  Then again, MAL hasn't quantified any of his desires either <wink>; I
bet he'd be happier with a BCD-ish scheme.

> ...
> Hmmm, port MPFR everywhere...?-)  Pearu Peterson already did the
> MPFR Python wrapper interoperating with GMPY, btw -- it lives at
> http://cens.ioc.ee/~pearu/misc/gmpy-mpfr/ (haven't tested it as
> I can't run MPFR myself, as above explained).

OK, that amounts to ~200 lines of C code to wrap some of the MPFR functions
(exp, log, sqrt, sincos, agm, log2, pi, pow; many remain to be wrapped; and
they don't allow specifying precision yet).  So Pearu still has significant
work to do here, while MAL is wondering who in their right mind would want to
do *anything* with numbers except add them <wink>.

hmm-he's-got-a-good-point-there-ly y'rs  - tim