Re: Experimenting with the Alpha build.

[Bill Allombert <allomber@math.u-bordeaux.fr>]

On Fri, Nov 07, 2003 at 12:09:56PM +0100, Karim BELABAS wrote:
> On Thu, 6 Nov 2003, Phil Carmody wrote:
> > --- Karim BELABAS <Karim.Belabas@math.u-psud.fr> wrote:
> >> On Thu, 6 Nov 2003, Phil Carmody wrote:
> >>> I was wondering if -ffast-math would do to Pari/GP/GMP on the alpha.
> >>> The speed-ups weren't significant on the whole (I should have tried
> >>> -mno-ieee too perhaps)
> >>
> >> This is expected: there's almost no floating point code in PARI (everything
> >> is emulated using 'unsigned long' arithmetic). Might be considered a
> >> shortcoming.
> >>
> >> There are lots of variables of type 'double', but they are used in parts of
> >> the code which is negligible timewise. And never where stability / accuracy
> >> is important. I.e --fast-math should be a no-op with respect to performances
> >> or results.
> >
> > I also recompiled GMP with -ffast-math too for the test. In theory GMP might
> > perform some FP maths (FFT multiplication? or is it NTT?).
> 
> NTT from a quick glance at the code. I don't think GMP uses doubles much,
> either. mp_limb_t is always a variant of some unsigned integer (int, long,
> long long).

What is NTT ? GMP FFT use modular arithmetic, not double.

Cheers,
Bill.