What do you guys thing about the P4

Richard Walsh rbw at networkcs.com
Fri Apr 13 12:45:47 PDT 2001

Phillip Matz wrote:

>Which brings up another question.  My current impression was that SSE/SSE2
>is only single-precision while G98 (and probably most computational
>chemistry programs) requires double-precision -> if this is correct then SSE
>doesn't help, rather, it invalidates ones G98 results.  Would anyone care to
>set me straight?

I think SSE---> 2 is what makes the difference.

Intel's write up on the P4 shows a packed double precision (IEEE 64-bit)
floating point data type (2 per XMM register) and goes on to say

"The SSE2 instructions have two primary functions.
    Permit packed [read small-vector] and scalar double-precision
    [read 64-bit] floating-point operations to be carried out in 
    the XMM [that's MMX backwards ... ;-)] registers.



I read that as a go for compiler developers wanting to improve their
compiler's double-precision (64-bit) performance on a P4. Bob Feller's
G98 benchmarks in an earlier posting confirm the excellent Gaussian
performance on the P4. 


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