Let's say we have the following code:
float f = 999999999999*9999999999999999*999999999999; //a large number to make it overflow
so according to the float-pointing rule, the result should be infinity as:
But I checked the result's bit representation , it is not the infinity, it is some else, how come?
None of the values in 999999999999*9999999999999999*999999999999 are floating points, so you aren't doing floating point arithmetic. In fact, even without any extra warning options set, gcc gives me this warning for your code (clang gives a similar warning):
warning: integer overflow in expression of type 'long int' results in '4467987020393345025' [-Woverflow]
Do this instead
float f = 999999999999.0f*9999999999999999*999999999999;
printf("%f\n", f);
output:
inf
Making the first literal a floating point number forces floating point arithmetic, so you get the infinite value you want.