implementation of isnan() function - c++

Question

I am a beginner to c++ programming and I am given a task of implementation of fixed point math arithmetic in c++. here I am trying to implementation a function isnan() which returns true if the number is not-a-number else will return false.
Test file
#include "fixed_point_header.h"
int main()
{
fp::fixed_point<long long int, 63> a=fp::fixed_point<long long int, 63>::positive_infinity(); // will assign positive infinity value to a from an function from header
fp::fixed_point<long long int, 63> b=fp::fixed_point<long long int, 63>::negative_infinity(); // will assign positive infinity value to b from an function from header
float nan=fp::fixed_point<long long int, 63>::isnan(a,b);
printf( "fixed point nan value == %f\n", float (nan));
}
In the header I want to do somewhat like the code shown below if positive and negative infinity values are added, the isnan function should return 1 else 0.
Header file
#include fixed_point_header
static fp::fixed_point<FP, I, F> isnan (fp::fixed_point<FP, I, F> x,fp::fixed_point<FP, I, F> y){
/*if ( x + y ) happens, ie. x and y are infinities
{
should return 1; }
else {
should return 0; }
} */
can anyone please tell how to proceed with it? or how to solve this paradigm

Answer 1

I am trying to implementation a function isnan() which returns true if the number is not-a-number else will return false.
That's simple enough; define a reserved value to represent nan (as you have for the infinities), and compare with that:
bool isnan(fixed_point x) {
return x == fixed_point::nan();
}
I want to do somewhat like the code shown below if positive and negative infinity values are added, the isnan function should return 1 else 0
It would be the responsibility of the addition operator to check the inputs and return nan if appropriate:
fixed_point operator+(fixed_point x, fixed_point y) {
if (x == fixed_point::nan() || y == fixed_point::nan()) {
return nan;
}
if (x == fixed_point::positive_infinity()) {
return y == fixed_point::negative_infinity() ? fixed_point::nan() : x;
}
// and so on
}
then the test in main becomes:
bool nan = fixed_point::isnan(a+b);