RE: [xsl] Addition/Subtraction of numbers.

[Wendell Piez <wapiez at mulberrytech dot com>]

Joshua,

At 06:24 PM 1/23/02, you wrote:
>I have the understanding that the XPath number() function will return the 
>string 'NaN' if the parameter passed in is not a number.

No, not exactly, it will return the number Not-a-Number (which if 
stringified comes out 'NaN').

>  Though, at a lower level, won't the same function called twice with 
> identical parameter(s) return the same thing?

Yes, it will (thank goodness).

>  So, when would your test of "number($t1) = number($t1)" fail?

When either number is Not-a-number. According to the Java Language 
Specification, which is cited by XPath (section 3.5) for its summary of the 
behavior of IEEE 754 double-precision numbers, "The equality operator == 
returns false if either operand is NaN" (of course in XPath the operator is 
'=' ... for now).

So NaN is not equal to itself.

It's confusing, but it comes with the territory of a number that is 
Not-a-Number. :-> Trust Jeni to be able to use this wrinkle productively.

Cheers,
Wendell

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