Re: Question on performance

[Arnold Neumaier <Arnold.Neumaier@xxxxxxxxxxxx>]

Paul Zimmermann wrote:
> > The problem in your example is not the inlining of the function 
> > nan2zero(). The problem is the function call isnan().
> > If you replace this function by a "x != x" then you will get a better 
> > performance which is close to the runtime without a call of nan2zero().
>
> right, but Arnold's explicitly mentioned a call to isnan(x).

Only for lack of knowledge that x!=x executes much faster.
Can someone explain _why_ this is so?

Are the predicates isfinite(x) and/or isinf(x) also much slower than
an arithmetic operation? Can they also be replaced by something
costing next to nothing?


Arnold Neumaier