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Old 2005-05-22, 03:32   #1

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Question How does prime95 use 3dnow?

24.11 whatsnew.txt says it now uses 3dnow instructions. What are they used for
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Old 2005-05-22, 08:16   #2
dsouza123's Avatar
Sep 2002

2·331 Posts

In the past Prime95 only used ALU (CPU integer), FPU (x87 floating point) and
SSE2 (SIMD/Vector floating point).
3DNow are SIMD for 32 bit floating point or integer but it is unlikely that 32 bit
floating point are used for LL because only a few bits of precision can be extracted
for FFT.
My guess is 3DNow is used for trial factoring somehow,
even though it works mainly with integer values about 64 bits in size.

Haven't looked at any code though to really findout.

It just may be a way of distingushing Athlon64/Opteron from Pentium 4/D
because only the AMD will have 3DNow but both have SSE2.
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Old 2005-05-22, 13:49   #3
P90 years forever!
Prime95's Avatar
Aug 2002
Yeehaw, FL

157448 Posts

Only the prefetchw instruction is used. On AMD machines this is better than using the prefetcht1 instruction.
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