NaN, Inf, isNaN, isInf - not-a-number and infinity functions
int isInf(double, int)
The IEEE floating point standard defines values called `not-a-number'
and positive and negative `infinity'. These values can be produced by
such things as overflow and division by zero. Also, the library func‐
tions sometimes return them when the arguments are not in the domain,
or the result is out of range. By default, manipulating these values
may cause a floating point exception on some processors but setfcr (see
getfcr(2)) can change that behavior.
NaN returns a double that is not-a-number. IsNaN returns true if its
argument is not-a-number.
Inf(i) returns positive infinity if i is greater than or equal to zero,
else negative infinity. IsInf returns true if its first argument is
infinity with the same sign as the second argument.