Guillermo Ballester Valor ([EMAIL PROTECTED]) writes:
<< You say your code is twice
faster than FFTW, sure it is, *BUT* in my pentium-166 the short code I
wrote do an iteration of my actual exponent 3975659 in 0.901 seconds
while mprime take only 0.359. This makes a RPI=40%. Then, your code will
reach nearly 90% !and without lots of assembler code! >>
Hi, Guillermo:
Alas, I don't think it works that way, for several reasons. On RISC
Microprocessors, instruction scheduling (while nontrivial) is much
easier than on CISCs, meaning that a good compiler can usually generate
code that runs nearly as fast as hand-tuned assembly code (ASM) written
by a skilled programmer. By "nearly" I mean 50-90%, depending on the
CPU, the compiler and the ASM programmer. Non-RISCs like the Intel x86
are notoriously difficult to generate good code for, either automatically
or by hand - I believe George spent 2 years getting the ASM for the early
versions of Prime95 put together, and he (George - correct me if I'm wrong)
was an x86 ASM expert to begin with.
I'm not familiar enough with the details of FFTW to say for sure (Steven
Johnson or Jason Papadopoulos could answer this), but I'm pretty sure
Frigo/Johnson have done some machine-specific ASM of critical portions
of the code, at least for some popular architectures - if so, the x86
would be one of the first candidates, for the above reason and the fact
that it's so numerous. That may explain why FFTW performs so well on
the x86. Whenever I've tried my code (not including v2.7 - that should
run at least 2x faster on x86 than 2.6, in my estimation) on x86, it's
been 5-10x slower than Prime95. (That's partly due to the fact that my
f90 compiler for x86 is awful, but only partly.)
>Is there any linux or window Mlucas 2.7 executable for intel machines?
No, but anyone with an f90 compiler for x86 is free to download and
compile the source. By far the best compiler I know of for x86 is the
Digital/Compaq/Microsoft Visual f90 for Windows - I don't have that
one to play with, unfortunately, but I'd be interested to hear from
someone who does what timings they get.
Regards,
Ernst
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