Re: [xsl] XSL Documentation: a number is true when...

[Norman Gray <norman@xxxxxxxxxxxxxxx>]

Kai, hello.

On 25 Jul 2007, at 10:57, Kai Hackemesser wrote:

>      a number is true if and only if it is neither positive or  
> negative
>      zero nor NaN<<
>
> My problem may be just lack of english language, but I need some  
> explanation here. What is meant by positive or negative zero? From  
> my math understandings zero is neither positive nor negative. If I  
> drop that and say, a number is true when the value is neither zero  
> nor NaN, would this be correct?

On essentially all significant hardware these days, floating point  
numbers are represented according to the IEEE 754 standard[1].   
Amongst other things, that includes special bit patterns for positive  
and negative infinity, a large set of bit patterns for NaN (not-a- 
number), and the property that zero can be signed, so that 1.0*0.0= 
+0.0 and -1.0*0.0 = -0.0.  The distinction matters in certain  
numerical contexts, but is ignorable for everyone else.

All the best,

Norman

[1] http://en.wikipedia.org/wiki/IEEE_754


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Norman Gray  :  http://nxg.me.uk
eurovotech.org  :  University of Leicester, UK