[Beowulf] Question about amd64 architecture and floating point operations

Ivan Paganini ispmarin at gmail.com
Wed Nov 22 03:01:54 PST 2006

Hello everybody at beowulf. Sorry about the _really_ newbie question, but
after doing some tests and researching a little, a question arose when
fooling around with amd64 (more precisely, an amd64 Athlon 4200 X2) and gcc
and sun studio 11. The architecture has 64 bits integer registers and 128
bits floating point registers, but my test programs in C just gave me the
same precision that I got with an old athlon 2400 xp (32bits), that is, long
double go only to 1x10^ 4961, even with the -m64 flag. I always imagined
that I would get the double precision without the long double declaration
(or, maybe, 40bits precision). What am I missing here? Is the compiler (gcc
4.1, sun studio express 11), the operating system (ubuntu 64bits edgy), or
just an error in my logic?

Thank you for the patience!

Ivan S. P. Marin
Laboratório de Física Computacional
Instituto de Física de São Carlos - USP
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