On Tue, 2013-03-05 at 18:54 +0100, Lionel Cons wrote:
> (1) in https://bugs.kde.org/show_bug.cgi?id=197915#c9 is a joke:
> >Julian Seward 2010-07-12 15:58:25 UTC
> > As per comment #0, adding support for 80-bit floats is low priority,
> > because (1) AIUI the majority of floating point code is portable
> > and restricts itself to 64-bit values,
>
> The majority of _consumer_ software uses using double (aka 64bit
> float), but the majority of _scientific_ software (for example the
> whole NIH bioinformtics software stack or 99.9% of CERNs simulation
> software) is relying on long long double aka 80bit or 128bit floats
> (depending on platform, AMD64 uses 80bits). valgrind is useless for
> such software.
I am not too sure about the proportion of consumer software
versus scientific software. Assuming there is more consumer software,
the note (1) above is not such a joke at the end :).
Reading the gcc manual, wouldn't it be a good idea to have the
scientific software to be rewritten (or at least compilable)
so as to use sse ?
gcc manual tells for `sse'
The resulting code should be considerably faster in the
majority of cases and avoid the numerical instability
problems of 387 code, but may break some existing code that
expects temporaries to be 80bit.
This is the default choice for the x86-64 compiler.
And as a bonus, you can run it under Valgrind on x86/amd64 :).
If this scientific code is fully portable, then you could also decide
to run it under Valgrind e.g. on ppc32/ppc64 systems.
Note: at my work, we are using Ada/gnat/gcc on x86/amd64.
The application code is compiled with sse.
We contemplated recompiling and/or changing the
Ada runtime to use sse only and fully avoid the 80 bits.
However, as at the end, we found very little impact (at least for
our apps) of running the 80 bits runtime on Valgrind, we have kept
the default gnat runtime (which uses 80 bits floats here and there).
As long as these 80 bits computation are "ok" if computation is
in reality done with 64 bits float, then not much impact.
YMMV.
Note that we have not got any indication that the original problem
of Bob is linked to 80 bits. Duncan's trials were succesful, I also
tried at work and at home, and always obtained the expected answer.
Philippe
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