//check the infinity
double x1=(double)0x7ff0000000000000;
double x2=(double)0x7ff0000000000001; // <=== not the ending 1
printf("nx1=%f, x2=%f sizeof(double) = %d", x1,x2, sizeof(x2));
if(x1==x2)
    printf("nx1==x2");
else
    printf("nx1!=x2");

x1=9218868437227405300.000000, x2=9218868437227405300.000000 sizeof(double) = 8
x1==x2