Bill Coffman wrote:
> NegNan doesn't exist, except as a fluke of the representation (see link for
> how they are represented). A -NaN is the same as a NaN. They both fail
> all
> comparison tests, even NaN == NaN is false (unless your compiler optimizes
> the comparison out). Only difference is the way they are stringified,
> which
> should be "NaN", but stringification of NaN is non-standard. Solaris
> compilers will print "-NaN", but gcc only prints "nan". Microsoft compiler
> prints strange stuff.
I am wondering if this NaN != NaN property could be used for the isnan
and finite tests, like so:
int
Parrot_math_isnan(double x)
{
return x != x;
}
int
Parrot_math_finite(double x)
{
return (!Parrot_math_isnan(x - x));
}
That is, if "x != x" it's a NaN. If x is finite, "x - x" should yield
something close to 0. Otherwise, "Inf - Inf" or "NaN - NaN", it's NaN.
Is this not portable enough? Is it better to look at the bits directly?
Ron
