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

[Jitse Niesen <jitse@xxxxxxxxxxxxxxxxx>]

On Tue, 22 Sep 2009, Benoit Jacob wrote:

> Sorry for adding to the currently already high traffic here.

Well, that's what the mailing list is for, isn't it?

> Here, on linux / x86, my programs run 100x slower when the
> floating-point values are 'inf' or 'nan'.

I seem to remember that this is a problem / feature in the design with 
Intel FPUs, but not with the AMD ones. Computations with these special 
values take longer, presumably because the people that designed the chip 
thought that they are not used often. Here's an article I found (it's from 
some time ago though): 
http://www.cygnus-software.com/papers/x86andinfinity.html

I never looked into it in detail though.

Cheers,
Jitse