>Henk Stokhorst wrote:
>>L.S.,
>>
>>Just curious, what makes factoring 13.388.659 take four times as
>>long as 13.375.793?
>
>It's because 13,388,659 is past the cutoff of 13,380,000 where
>Prime95 starts factoring to the depth of 2^65 instead of 2^64.
>Normally, increasing the depth by a factor of one only doubles
>the time required. However, because of the nature of chip architecture, it
>takes a longer period of time than normal
>above 2^62 and again above 2^64 to do the necessary
>calculations (more instructions and such).
Now, I may be totally off base here, but...
The reason is because the integer part of the Intel CPU is 64 bit...okay, so
Prime95 does some additional steps to provide greater bit depth factoring...
Now, if that's really the case, would it be of any advantage to have the FPU
handle factoring? I know that some processors only do factoring because
they have a slow FPU to begin with (like Cyrix and AMD K6 chips), but would
a Pentium be able to use it's FPU to do trial-factoring to greater bit
depths any faster than the software based solution George uses beyond 64
bits?
Just curious...
Better yet, do any of the wacky SIMD/MMX/3DNow instructions provide any
possible benefits for trial factoring? I recall a discussion before about
how those instructions wouldn't be too useful for LL testing because of they
only handle double-word sized data (32 bits), but for trial-factoring...any
uses?
Aaron
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