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This section describes some miscellaneous test functions on doubles.
Prototypes for these functions appear in `math.h'. These are BSD
functions, and thus are available if you define _BSD_SOURCE or
_GNU_SOURCE.
Function: int isinf (double x)
This function returns -1 if x represents negative infinity,
1 if x represents positive infinity, and 0 otherwise.
Function: int isnan (double x)
This function returns a nonzero value if x is a "not a number"
value, and zero otherwise. (You can just as well use x !=
x to get the same result).
Function: int finite (double x)
This function returns a nonzero value if x is finite or a "not a number" value, and zero otherwise.
Function: double infnan (int error)
This function is provided for compatibility with BSD. The other
mathematical functions use infnan to decide what to return on
occasion of an error. Its argument is an error code, EDOM or
ERANGE; infnan returns a suitable value to indicate this
with. -ERANGE is also acceptable as an argument, and corresponds
to -HUGE_VAL as a value.
In the BSD library, on certain machines, infnan raises a fatal
signal in all cases. The GNU library does not do likewise, because that
does not fit the ANSI C specification.
Portability Note: The functions listed in this section are BSD extensions.
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