NaN

[ark at alice.UUCP]

In article <660011 at hpclscu.HP.COM>, shankar at hpclscu.UUCP writes:
 
> Thus, it's kind of difficult to do a thing like:

>    if (f == NaN) { /* .. */ }

Not if traps are disabled.  NaN is not equal to anything, so you
can simply say

	if (f != f) { /* ... */ }

> How's about
 
>    #define NaN (1.0 / 0.0)
 
Nope.  1.0/0.0 is infinity, not NaN.  However, if appropriate traps
are disabled, 0.0/0.0 is a NaN.

> A good solution would be to add a few routines to libm.a

IEEE recommends specific routines, though I've forgotten what they are.
Of course, any such routines will only work on machines with IEEE
floating point (or equivalent).