Re: [Gnash-commit] gnash ChangeLog server/as_value.cpp server/as_v...

[Eric Hughes]

At 11:24 PM 7/8/2007, zou lunkai wrote:
> For swf>=5, The observed results here are:
>
> trace(NaN == NaN);   //true
> trace(NaN >= NaN);   //true
> trace(NaN <= NaN);  //true
> trace(NaN > NaN);    //undefined
> trace(NaN < NaN);    //undefined
> trace(NaN != NaN);   //false

I'm just whinging here, but all these should return "undefined" in the 
mathematically-correct world.  If the comparisons are on numbers, and you 
have a meta-value that means not-a-number, but the comparisons between 
numbers, as functions on the set "numbers union special-value" would be 
partial functions defined only on pairs of numbers and be undefined if one 
or both elements of the pair were not a number.

This is less purely academic that it sounds.  Not-a-number means "I have no 
information".  It does not mean "I have a special new kind of number with 
special axiomatic properties".  To say that "a=b" when both are not a 
number means asserting that "I have no information about a, and I have no 
information about b, but I know they're the same."  Put this in some 
generic algorithm with wonky input data, and you'll get an unintended 
(therefore incorrect) result.

This is all FYI.  I am promoting no cause to fix AS.

Incidentally, this argument isn't the same for underflow and overflow 
meta-values.  Overflow creates a compact representation of infinity, and 
underflow creates a non-Haussdorf point at 0, i.e. three topologically 
inseparable values, but these are still well-defined spaces.

Eric