Christoph Groth wrote:
<snipped inconsistent floating point results>
This is on a computer with an Intel Core 2 CPU (I tried several
different variants).
If I take the second (-O1) binary and execute it on an Opteron it
produces the _first_ result. Thus, the same static binary produces
different results on different processors!
This is a hardware-related effect - in a nutshell, it happens because Intel
hardware can extend double-precision floating point operations to 80 bits
internally, whereas AMD hardware usually enforces 64 bits at all times.
Here's a link to an old message from when I encountered the same problem and
people on this list helped me out:
http://gcc.gnu.org/ml/gcc-help/2005-12/msg00062.html
The links in that message point to articles which detail exactly why this sort
of thing happens. Once you understand the problem, you'll need to read through
the various floating point and optimisation related options for your compiler,
then choose a set which provide you with an acceptable compromise.
I observe this problem also with g++ 4.4.2.
As this is a hardware-related effect, it can happen to you with any version of
any compiler, not just GCC.
Hope that helps!
Neil.
