redhat man page for isnan

ISINF(3)						     Linux Programmer's Manual							  ISINF(3)

NAME
       isinf, isnan, finite - test for infinity or not-a-number (NaN)

SYNOPSIS
       #include <math.h>

       int isinf(double value);

       int isnan(double value);

       int finite(double value);

DESCRIPTION
       The isinf() function returns -1 if value represents negative infinity, 1 if value represents positive infinity, and 0 otherwise.

       The isnan() function returns a non-zero value if value is "not-a-number" (NaN), and 0 otherwise.

       The finite() function returns a non-zero value if value is neither infinite nor a "not-a-number" (NaN) value, and 0 otherwise.

CONFORMING TO
       BSD 4.3

GNU
								    1993-06-02								  ISINF(3)