Your "isodd" function should probably not be doing bounds checking and throwing an error when it encounters large even integers.
If you have a use case where you need to know if you multiplied two large integers and got a result larger than 2^53, then you should do it explicitly before you get to the point of checking if your number is even or odd.
If you have a use case where you need to know if you multiplied two large integers and got a result larger than 2^53, then you should do it explicitly before you get to the point of checking if your number is even or odd.