ISINFF(3) Library Functions Manual ISINFF(3)

isinff, isnanf
test for infinity or not-a-number

Math Library (libm, -lm)

#include <math.h>

int
isinff(float);

int
isnanf(float);

The isinff() function returns 1 if the number is “infinity”, otherwise 0.

The isnanf() function returns 1 if the number is “not-a-number”, otherwise 0.

isinf(3), isnan(3), math(3)

IEEE Standard for Binary Floating-Point Arithmetic, Std 754-1985, ANSI.

Neither the VAX nor the Tahoe floating point have distinguished values for either infinity or not-a-number. These routines always return 0 on those architectures.
August 16, 1999 NetBSD 9.2