## digitalmars.D - Disable NaN and Inf

- Jonathan Crapuchettes <jcrapuchettes gmail.com> Feb 05 2010
- Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> Feb 06 2010
- =?ISO-8859-1?Q?Pelle_M=E5nsson?= <pelle.mansson gmail.com> Feb 06 2010
- dsimcha <dsimcha yahoo.com> Feb 06 2010
- Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> Feb 06 2010
- Don <nospam nospam.com> Feb 06 2010
- Jonathan Crapuchettes <jcrapuchettes gmail.com> Feb 06 2010
- BCS <none anon.com> Feb 06 2010
- Trass3r <un known.com> Feb 06 2010

I would like to divide one array by another using the slice syntax so that I can benefit from the vectorized operation, but I am running into a problem. Some of the numbers is my denominator array are 0, producing NaNs and Infs in the result. My question is: Is there a way to force 0/0 and x/0 to result in 0? Thank you, JC

Feb 05 2010

Jonathan Crapuchettes wrote:I would like to divide one array by another using the slice syntax so that I can benefit from the vectorized operation, but I am running into a problem. Some of the numbers is my denominator array are 0, producing NaNs and Infs in the result. My question is: Is there a way to force 0/0 and x/0 to result in 0? Thank you, JC

I don't know of a way. You may want to try first running a loop replacing 0 with inf throughout the denominator array. Then run vectorized division; any non-inf divided by inf yields 0. Andrei

Feb 06 2010

On 02/06/2010 09:16 AM, Andrei Alexandrescu wrote:Jonathan Crapuchettes wrote:I would like to divide one array by another using the slice syntax so that I can benefit from the vectorized operation, but I am running into a problem. Some of the numbers is my denominator array are 0, producing NaNs and Infs in the result. My question is: Is there a way to force 0/0 and x/0 to result in 0? Thank you, JC

I don't know of a way. You may want to try first running a loop replacing 0 with inf throughout the denominator array. Then run vectorized division; any non-inf divided by inf yields 0. Andrei

divide several other arrays. A single pass will be faster and more clear, I think.

Feb 06 2010

== Quote from Andrei Alexandrescu (SeeWebsiteForEmail erdani.org)'s articleJonathan Crapuchettes wrote:

replacing 0 with inf throughout the denominator array. Then run vectorized division; any non-inf divided by inf yields 0. Andrei

At this point it's probably useless to vectorize, though. You may as well just write something like: if(isNaN(arr2[i])) { result[i] = 0; } else { result[i] = arr1[i] / arr2[i]; }

Feb 06 2010

dsimcha wrote:== Quote from Andrei Alexandrescu (SeeWebsiteForEmail erdani.org)'s articleJonathan Crapuchettes wrote:

replacing 0 with inf throughout the denominator array. Then run vectorized division; any non-inf divided by inf yields 0. Andrei

At this point it's probably useless to vectorize, though. You may as well just write something like: if(isNaN(arr2[i])) { result[i] = 0; } else { result[i] = arr1[i] / arr2[i]; }

I don't know. In such cases only experimentation can prove anything. Andrei

Feb 06 2010

Andrei Alexandrescu wrote:dsimcha wrote:== Quote from Andrei Alexandrescu (SeeWebsiteForEmail erdani.org)'s articleJonathan Crapuchettes wrote:

replacing 0 with inf throughout the denominator array. Then run vectorized division; any non-inf divided by inf yields 0. Andrei

At this point it's probably useless to vectorize, though. You may as well just write something like: if(isNaN(arr2[i])) { result[i] = 0; } else { result[i] = arr1[i] / arr2[i]; }

I don't know. In such cases only experimentation can prove anything. Andrei

I think it would depend heavily on cache effects. If it fits into the L1 cache, my guess is that doing a vectorized check followed by a vectorized division would be faster. But it's extremely difficult to predict this kind of thing. If the array is larger than the cache, the per-element check would definitely be much quicker, since you'd only have one cache miss instead of two.

Feb 06 2010

Are NaNs and Infs the result of a CPU operation or is that part of the D language? JC Andrei Alexandrescu wrote:Jonathan Crapuchettes wrote:

I don't know of a way. You may want to try first running a loop replacing 0 with inf throughout the denominator array. Then run vectorized division; any non-inf divided by inf yields 0. Andrei

Feb 06 2010

Hello Jonathan,Are NaNs and Infs the result of a CPU operation or is that part of the D language?

The Floating point unit does all of that and IIRC it's defined as part of the IEEE standard. -- <IXOYE><

Feb 06 2010

Are NaNs and Infs the result of a CPU operation or is that part of the D language?

http://en.wikipedia.org/wiki/NaN

Feb 06 2010