Comparing for NaN

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Kevin E.
Loveland, CO

Jul 28, 2010
4 Posts

1 ✔  |  ✗ 0  

Re: Comparing for NaN

My ATEasy application uses a 3rd party DLL with functions that may return an IEEE NaN (Not a Number).  Does ATEasy have a built-in means to determine if the value (as a float or double) is a NaN?

DrATEasy (Ron Y.)
Mission Viejo, CA

Jul 28, 2010
358 Posts

0 ✔  |  ✗ 0  

Re: Comparing for NaN

Take a look at the following example:

ddwQNaN:DDWord
d:Double
dQNaN:Double

ddwQNaN=0xFFF8000000000000
MemoryCopy(&dQNaN, &ddwQNaN, 8)
print d  ! will print  -1.#IND
d=dQNaN
print d
if ddQNaN=d
    print "same"
endif

You can do the same for any NaN representation.

Aaron R.
Tucson, AZ

Jan 6, 2011
9 Posts

0 ✔  |  ✗ 0  

Re: Comparing for NaN

I do not have my ATEasy environment available right now.  Does the if test pass and same prints out?

DrATEasy (Ron Y.)
Mission Viejo, CA

Jan 7, 2011
358 Posts

0 ✔  |  ✗ 0  

Re: Comparing for NaN

Yes, it will print "same".

Aaron R.
Tucson, AZ

Jan 7, 2011
9 Posts

0 ✔  |  ✗ 0  

Re: Comparing for NaN

Ron, I would submit that is incorrect behavior. A NaN is not equal to anything, even itself. Looking at IEEE754 will confirm this behavior. The correct test for a NaN in languages like C, C++, and python is:

if x != x

python implements an isNaN() function as well.

I would suggest creatiion of an isNaN type procedure and the equality comparison be changed to false when comparing two NaNs to fall inline with IEEE754.

Wikipedia has a discussion of NaN: http://en.wikipedia.org/wiki/NaN which echoes the behavior I mentioned.

DrATEasy (Ron Y.)
Mission Viejo, CA

Jan 7, 2011
358 Posts

0 ✔  |  ✗ 0  

Re: Comparing for NaN

You are right, it should not print (according to IEEE754). I will add it to our suggestion list. BTW why do you need this?

Aaron R.
Tucson, AZ

Jan 11, 2011
9 Posts

0 ✔  |  ✗ 0  

Re: Comparing for NaN

Ron -

I don't have an immediate need, but was trying to be complete for when the situation comes up in the future.  Kevin's original question sounded like a perfect example of what can happen when interfacing with an external DLL.



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