What is the correct way to obtain (-1)^n?

Question

Many algorithms require to compute (-1)^n (both integer), usually as a factor in a series. That is, a factor that is -1 for odd n and 1 fo

Answer 1

If it's speed you need, here goes ...

int inline minus_1_pow(int n) {
    static const int retvals[] {1, -1}; 
    return retvals[n&1];
}

The Visual C++ compiler with optimization turned to 11 compiles this down to two machine instructions, neither of which is a branch. It optimizes-away the retvals array also, so no cache misses.