[m-users.] Too Slow

Delmas Buckley rbuckley at ieee.org
Wed Apr 15 09:31:40 AEST 2015

Thank you, Matthias. The fix you propose is beyond my programming skills
and my interest level. But you've given me insight into where the problem
lies. I think the memory blowup problem may be the result of the "rho/1"
procedure being coded in such a way that it isn't tail recursive. That
problem, I can tackle.

Best regards,
Robert Buckley

On Tue, Apr 14, 2015 at 10:39 AM, Matthias Guedemann <matthias at guedemann.org
> wrote:

> Hi Robert,
> > -disable-most-grades option. I am very disappointed with the slowness
> > of the procedures written for Mercury, and sometimes memory usage
> > begins to blow up (slowly, over time as the process runs. Some of
> > these run overnight). When I say I'm disappointed in the Mercury
> > performance, I mean that by comparison with similar procedures I run
> > written in Prolog, Erlang, Haskell, and Scheme, Mercury is much too
> > slow, often taking 10 times or more as much time to complete. The
> > Mercury runs I've made (not including those abandoned because of
> > memory blowup) do complete and get correct results, but take way too
> > much time to run.
> In my opinion, the principal reason for this is that the Mercury
> implementation for big integers is written in pure Mercury. In contrast,
> Haskell calls GMP via FFI. GMP is a highly optimized library written in
> C. For the other languages, it depends on the implementation, but very
> likely they also use GMP or a similar library directly. The downside of
> using GMP or another library is the added dependency, of course.
> > Does anyone have any suggestions for speedup, other than "Avoid using
> > Mercury for this purpose"? I'm attaching copies of the source code of
> > the procedures that run so slowly.
> A while ago, I implemented a faster multiplication algorithm for Mercury
> (parallel for asm_fast.par.gc.stseg), but IIRC Miller-Rabin requires
> primarily fast modulo and division. I am interested in optimizing these
> routines, too, but have not yet put any work into it. In my opinion,
> there is potential in optimizing the division and modulo algorithms and
> maybe also in optimizing the representation of big integers (currently
> lists of 14 bit digits), but to be honest, I think that reaching the
> speed of anything based directly on GMP is unrealistic.
> Best regards,
> Matthias
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