| ISNAN(3) | Library Functions Manual | ISNAN(3) | 
isnan —
#include <math.h>
int
  
  isnan(real-floating
    x);
isnan() macro determines whether its argument
  x is not-a-number (“NaN”). An argument
  represented in a format wider than its semantic type is converted to its
  semantic type first. The determination is then based on the type of the
  argument.
isnan() macro returns a non-zero value if the value
  of x is a NaN. Otherwise 0 is returned.
IEEE Standard for Binary Floating-Point Arithmetic, Std 754-1985, ANSI.
isnan() macro conforms to ISO/IEC
  9899:1999 (“ISO C99”).
isnan() function always returns 0, as the
  architecture doesn't support NaN.
| September 27, 2017 | NetBSD 10.0 |