7.12.3.3 The isinf macro
Synopsis
#include <math.h>
int isinf(real-floating x);
Description
The isinf macro determines whether its argument value is an infinity (positive or negative). First, an argument represented in a format wider than its semantic type is converted to its semantic type. Then determination is based on the type of the argument.
Returns
The isinf macro returns a nonzero value if and only if its argument has an infinite value.