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

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*To*: eigen@xxxxxxxxxxxxxxxxxxx*Subject*: Re: [eigen] (General question) Floating point: why are 'inf' and 'nan' slow?*From*: Benoit Jacob <jacob.benoit.1@xxxxxxxxx>*Date*: Wed, 23 Sep 2009 11:28:07 -0400*Dkim-signature*: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:received:in-reply-to:references :date:message-id:subject:from:to:content-type; bh=sMXkKz7SvzZ6o9UbfAXR3fIDto7w9B+yO4ff2iHq52M=; b=BWctPCGAqiwdYIBAdqTaSWdzFx10xG0oOS7TvA8VjrhdgXrM40WtHn0AqDp20R2GvM N6x+v+bxm/tgovNz7Y67JFiMgYmtwvAfwt8z6aIouQrdjQtXUjnJvRMRTBeP8RK7q4gp 1BJUeS+FZOOmmef+3LlX6xqlW4E6Jpt/hqAaY=*Domainkey-signature*: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :content-type; b=FwBbtXnbwgpGFyBSlJ9/9LZKcCwQLW1tsFa9YS3HEDg//ms4J7mt8UtmirpmJCYs/0 LQXkSV8WEppApKFCd8TKrZ2kgNz7BVhtay8O2fjLYLo4KVaNr85gvNHBzJYTIMuZUUJi oGrI7xjrzEf+OdENxPjZQZKcuD4T26SH8nnI0=

2009/9/23 Jitse Niesen <jitse@xxxxxxxxxxxxxxxxx>: >> 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. > OK, thanks for the link, that was interesting. I confirms exactly my experience (I have a Core 1 Duo so it's not specific to the Pentium 4). It is interesting that it mentions that, while the issues with INF and NAN are specific to Intel non-SSE, the issues with denormals are universal. For Eigen though, the big issue is INF and NAN. Benoit

**References**:**[eigen] (General question) Floating point: why are 'inf' and 'nan' slow?***From:*Benoit Jacob

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

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