How can I detect integer overflow on 32 bits int?

Question

I know such topic was asked several times, but my question is about overflow on full 32 bits of int. For example:

  11111111111111111111111         


        

Answer 1

The most intuitive method I can think of: calculate the sum (or difference) as a long, then convert that sum to an int and see if its value has changed.

long longSum = (long) a + b;
int sum = (int) longSum;
if (sum == longSum) {
    // sum contains the correct result
} else {
    // overflow/underflow
}

Remember that on modern 64 bit processors, working with longs is no less efficient than working with ints (the opposite may be true). So if you have a choice between checking for overflows or using longs, go for the latter.