Re: [eigen] (General question) Floating point: why are 'inf' and 'nan' slow?

[Robert Bocquier <robert.bocquier@xxxxxxxxxxx>]

Benoit Jacob a écrit :
> Hi,
>
> Sorry for adding to the currently already high traffic here.
>
> Here, on linux / x86, my programs run 100x slower when the
> floating-point values are 'inf' or 'nan'.
>
> Only scalar code is affected, SSE code is not affected.
>
> I haven't enabled floating-point exception signals. I don't have a FP
> signal handler. Just any basic c++ program.
>
> Can this be "fixed"? How?
>
> Otherwise, I really need to make sure that solve() methods avoid
> producing such special values when no solution exists --- otherwise
> they take much longer to return.
>
> Thanks for your help,
> Benoit
>
>
>
>   
Hi Benoit,
may be *before* arriving to those extremes you've encountered
"denormalized numbers" ?
There are provisions to get rid of them with SSE, while in regular "387"
code you must explicitly deal with them. This is consistent with your
observation (but it's not a proof).

Best,
-- 
Robert Bocquier


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