[Openmcl-devel] Fun with Measurements

[Gary Byers]

On Sat, 28 Oct 2006, Brent Fulgham wrote:

>
> While the 64-bit build of OpenMCL looks great on nearly all tests
> (and substantially improves over the 32-bit build in some cases),
> something seems very wrong with the 64-bit support for BIGNUMS (see
> BIGNUM/PARI-200-5, PI-DECIMAL/BIG and PI-DECIMAL/SMALL for example).
> Remember that the non-reference columns are relative scales, so on PI-
> DECIMAL/SMALL, 64-bit OpenMCL is 10x as slo as OpenMCL 1.1/1.0 in 32-
> bit.  One small bright spot is the CRC40 benchmark, which due to it's
> heavy use of 40-bit integers is substantially improved using native
> 64-bit words.

I haven't looked at this (Apple's CHUD performance tools don't yet work
in 64-bit mode); can you tell whether it's more accurate to say "bignum
arithmetic is slower in ppc64 OpenMCL" or "bignum -multiplication- is
slower ..." ?

The ppc32 version does Karatsuba multiplication
<http://en.wikipedia.org/wiki/Karatsuba_multiplication> if the
operands are big enough; neither the ppc64 nor x86-64 versions do (for no
particularly good reason.)  I'd be a little surprised if that was the difference,
but I'm also surprised by the results: a year of so ago, the ppc64 bignum code
seemed as fast or faster in all of the cases that I tried.