[Beowulf] Peformance penalty when using 128-bit reals on AMD64

Prentice Bisbal prentice at ias.edu
Fri Jun 25 10:35:52 PDT 2010

Nifty Tom Mitchell wrote:
> On Fri, Jun 25, 2010 at 10:28:15AM -0400, Prentice Bisbal wrote:
>> Beowulfers,
>> One of my Fortran programmers had to increase the precision of his
>> program so he switched from REAL*8 to REAL*16 which changes the size of
>> his variables from 64 bits to 128 bits. The program now takes 32x longer
>> to run.
> I am surprised that it works as support in things like
> the math lib, log and trig functions could be missing.
> Which compiler is he using?

I'm 99% sure he's using the Intel Fortran Compiler, ifort.


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