On Sat, 17 Jun 2000 [EMAIL PROTECTED] wrote:
> Will Prime95 be rewritten to run on the Itanium, when it comes out? Seems to
> me like 64-bit operation will speed it up significantly, as will the insane
> amount of registers and floating point units and all the other
> microprocessor
> whatnot that I'm not current on.
Intel has had documentation available on the Web for a while that details
the architecture of Itanium. If Prime95 is ever rewritten for IA64 it
would have to be not only a total rewrite but a complete rethinking of
the FFTs it uses. For example, integer multiply-adds take only a little
longer than floating point multiply-adds; should IA64Prime use an integer
or floating point FFT? If integer, there are big delays in shuffling
between integer and FPU registers (only the FPU can multiply). If floating
point, loads and stores will all take longer, the cache behavior is
totally different, and the arrays involved get longer because you can't
pack bits as densely as an integer solution.
Itanium can do two FPU operations per clock, but both can be multiply-adds
instead of just multiplies or adds. Can you rearrange a real-valued FFT
to use multiply-adds as much as possible? It could cut the operation count
in half if you do, but to my knowledge no one has yet done so. It's been
done for complex FFTs, but Prime95 really wants real-valued FFTs, not
complex ones.
Moving to IA64 will be a much bigger challenge than simply rewriting
half a meg of assembly language.
jasonp
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