Phil Carmody on Thu, 06 Nov 2003 21:52:41 +0100

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Re: Experimenting with the Alpha build.

--- Karim BELABAS <> 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?). I wasn't expecting
massive changes, I just fancied experimenting. 

The only ones that had an improvement more than the 
likely noise floor were:

* Testing analyz        for gp-sta..TIME=445    for gp-dyn..TIME=399
* Testing number        for gp-sta..TIME=226    for gp-dyn..TIME=231

vs. the "slow" old

* Testing analyz        for gp-sta..TIME=463    for gp-dyn..TIME=411
* Testing number        for gp-sta..TIME=242    for gp-dyn..TIME=243

analyz is a bit weird - I was expecting -dyn to by slower than -sta 
across the board.

> I have just dumped this part of the result in CVS. Same goes for bnfinit, and
> a few other diagnostics which have cluttered outputs for no good reason
> ( bnfisprincipal / bnrisprincipal ).
> The minor backward incompatibility should not pose a problem, since I do not
> see any situation where this component would need to be accessed.

Heheh, sorry for diverting you onto trivialities. 
Experimentation is in my nature, alas...


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