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 13:56:31 -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=Reli+FFDgy/SsIEPLvHoW2IVR7C4wuDoH2uB+PyI2KA=; b=TFdy/jzibxGQ29D2bPw5EarVQEU4C9aYAqjPvA8SrALPyg0oXd5w6IDrVhWPixNNTB pJ6Mfh59VIqT8oxBaQYR9EMEm6Q6r5ihdfc7iNb0CWiXWeMW2HpTVv1rx4VbjVTMX2Zb fZ0SKJSTRhPe7h+XuWQwwaGxlvxzwAWx8Nvq8=*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=wqNt9FFqWjV50igFKa3rxRa0Oo+xSSY1BUBNk4MyeWot+nHRFm5sPpS49IMMrkEeHL tch5TMd9/5NVBvHY4dkJqzr3iq5VsUSIe7YeZ8ONWjsmEivY7Ewum/bxyXiEE7Qz96g8 q99F85pqr3Vamp3cM7VQMEU7Y3fW7k7bm9VNU=

2009/9/23 Rohit Garg <rpg.314@xxxxxxxxx>: > On Wed, Sep 23, 2009 at 10:27 PM, Benoit Jacob <jacob.benoit.1@xxxxxxxxx> wrote: >> The list of x86 CPUs that don't have SSE2 (SSE is not enough for >> double) includes Pentium 3, Athlon XP, VIA C7, AMD Geode, etc. There's >> no way that we could neglect all of them performance-wise. Moreover, >> even with SSE2, people may still want to use -mfpmath=387 (and it's >> the default) in which case the non-vectorized part of Eigen >> computations is affected. >> >> It's not a corner case at all, I was wondering if when redesigning the >> solvers I could assume it to be safe to produce INF and NAN during the >> computation, not just as return values at the end, and the answer is >> that I can't do that. > > How do you propose to handle this then? Will you check for values > before writing them to memory? And what happens on the SSE2 machines? > There too, denormals are handled in sw. I don't need to handle all cases, it's OK if in corner cases I have INF values. All I need to take care of is the "mainstream" cases. This is far easier :) Current Eigen already does that, as does LAPACK. 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:*Rohit Garg

**Re: [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:*Rohit Garg

**Re: [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:*Rohit Garg

**Re: [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:*Rohit Garg

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