__builtin_cpow((0,0),(0,0))

[Ronny Peine]

Hi,

Kai Henningsen wrote:
> dewar@adacore.com (Robert Dewar)  wrote on 07.03.05 in <422CFBA7.8080001@adacore.com>:
> 
> 
>>Ronny Peine wrote:
>>
>>
>>>Sorry for this, maybe i should sleep :) (It's 2 o'clock here)
>>>But as i know of 0^0 is defined as 1 in every lecture i had so far.
>>
>>Were these math classes, or CS classes.
> 
> 
> Let's just say that this didn't happen in any of the German math classes I  
> ever took, school or uni. This is in fact a classic example of this type  
> of behaviour.
> 
> 
>>Generally when you have a situation like this, where the value of
>>the function is different depending on how you approach the limit,
>>you prefer to simply say that the function is undefined at that
>>point.
> 
> 
> And that's how it was always taught to me.

Well yes, in the general case this is the right way. But for some 
special cases a definition is used to simplify mathematical sentences as 
it is done for 0^0 = 1 or gcd(0,0,...,0) = 0. See for example:
http://mathworld.wolfram.com/ExponentLaws.html

Even though, gcc returns 1 for pow(0.0,0.0) in version 3.4.3 like many 
other c-compiler do. The same behaviour would be expected from cpow.

> 
> 
> This is, of course, a different question from what a library should  
> implement ... though I must say if I were interested in NaNs at all for a  
> given problem, I'd be disappointed by any such library that didn't return  
> a NaN for 0^0, and of any language standard saying so - I'd certainly  
> consider a result of 1 wrong in the general case.
> 
> MfG Kai
> 
>


cu, Ronny