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digitalmars.D - Disable NaN and Inf

reply Jonathan Crapuchettes <jcrapuchettes gmail.com> writes:
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
parent reply Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:
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
next sibling parent =?ISO-8859-1?Q?Pelle_M=E5nsson?= <pelle.mansson gmail.com> writes:
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
prev sibling next sibling parent reply dsimcha <dsimcha yahoo.com> writes:
== Quote from Andrei Alexandrescu (SeeWebsiteForEmail erdani.org)'s article

 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



 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
parent reply Andrei Alexandrescu <SeeWebsiteForEmail erdani.org> writes:
dsimcha wrote:

 == Quote from Andrei Alexandrescu (SeeWebsiteForEmail erdani.org)'s article

 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



 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
parent Don <nospam nospam.com> writes:
Andrei Alexandrescu wrote:

 dsimcha wrote:

 == Quote from Andrei Alexandrescu (SeeWebsiteForEmail erdani.org)'s 
 article

 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



 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
prev sibling next sibling parent reply Jonathan Crapuchettes <jcrapuchettes gmail.com> writes:
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 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
parent BCS <none anon.com> writes:
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
prev sibling parent Trass3r <un known.com> writes:
 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