[Openmcl-devel] bignums on x8664 (and ppc64, too)

R. Matthew Emerson rme at clozure.com
Fri Sep 18 17:32:48 UTC 2009


On Sep 15, 2009, at 10:29 PM, R. Matthew Emerson wrote:

> I just checked in a change to the trunk (http://trac.clozure.com/openmcl/changeset/12839
> ) that tries to multiply bignums on x8664 64-bits at a time.
>
> Unfortunately, I'm not really sure whether this is a net win as
> currently implemented.  On the one hand, trivial benchmarks like (time
> (null (fact 10000))) seem to show a small performance regression with
> this new change.  On the other hand, the little benchmark in http://clozure.com/pipermail/openmcl-devel/2008-October/008591.html
>  shows an improvement.
>
> I would be very interested to hear from users who use bignums a lot to
> see if this change makes a positive difference.   Otherwise, it might
> make sense to take it back out.

There's also a specialized function to multiply a bignum by a fixnum.   
After updating that, (fact 10000) runs in half the time.  (gb  
explained to me in small words that FACT is all about multiplying a  
bignum by a fixnum.)

I think this bignum change is probably a win after all.




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