/-INFINITY and NaN

[John Gilmore]

Sun Unix uses IEEE float.  They provide library routines isnan() and isinf().
Note that there are two infinite values (positive and negative) and many
NaNs, so a simple compare to a single value is not good enough.

These library routines seem to be a good idea, since they can be implemented
for all kinds of float (eg, Vax, IBM) and increase portability.  (A system
without infinites or NaNs would always return false of course.)