use decimal

Maciej Stachowiak mjs at apple.com
Thu Sep 18 17:22:04 PDT 2008


On Sep 18, 2008, at 5:13 PM, Mark S. Miller wrote:

> On Thu, Sep 18, 2008 at 4:52 PM, Brendan Eich <brendan at mozilla.org>  
> wrote:
> -0 and 0 are not the same "given floating point number". 1/-0 vs.  
> 1/0 and Math.atan2(-0,0) vs. 0,0 are but two examples.
>
> Yes, I understand their operational difference. Whether that  
> difference means they are not the same number depends on how you  
> define "number". I would have defined "representing the same number"  
> by correspondence to the reals. YMMV.

But the mathematical behavior of floating point numbers is not the  
same as that of the reals. Not just because of -0. See <http://docs.sun.com/source/806-3568/ncg_goldberg.html 
 >

Floating point numbers are a useful rough approximation of the reals  
for many practical calculations, but treating them as if they were in  
fact a subset of the reals is not mathematically sound.

> In any case, my question is, does there exist any similar  
> operational difference between decimal floating point values that  
> are considered to be in the same cohort? If not, then I back Sam's  
> proposal without compareTotal().

I assumed not, but it would be nice to hear from an expert.

If there is an operational difference (in the sense you helpfully  
expressed in more precise form) then I tend to think it undermines the  
notion of cohort.

Regards,
Maciej

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