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From: Roland M. <rol...@nr...> - 2017-06-01 11:47:01
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On Mon, May 29, 2017 at 1:20 PM, FEVOTTE Francois
<fra...@ed...> wrote:
> Dear Valgrind developers,
>
> first, please forgive us if this post is out of place in this list.
>
> We would like to introduce Verrou [1], a floating-point error diagnostics
> tool based on Valgrind. The idea behind the tool is that it replaces all
> floating-point operations by randomly rounded ones (which means that instead
> of always rounding non-representable results to the nearest floating-point
> number, one of the two nearest floating-point numbers is chosen randomly).
It would be nice to be able to "define" the randomness here, e.g. by
providing a pseudo-random-number generator and a command line option
to provide the "seed" value. Point is that you can actually debug
issues in a deterministic&&repeatable way *IF* they happen.
> Instrumented program results thus become realizations of a random variable,
> the dispersion of which gives an estimation of the impact of the
> accumulation of floating-point round-off errors during program execution. In
> the computer arithmetic community, this technique is known as an
> asynchronous CESTAC method, which is a variant of Monte-Carlo arithmetic.
> More details can be found in Verrou's user manual [2].
>
> This work was pursued at EDF R&D [3], but we think such a tool might be of
> broader interest, especially since Valgrind's "Project Suggestions" page
> lists the detection of floating-point inaccuracies as a topic of interest.
Another issue is to make sure things like +nan/-nan and NaNs with
payloads work correctly with your tool since there are lots of
applications which use this kind of stuff for error ("error" as in
"error message") propagation.
----
Bye,
Roland
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