The following function computes X^Y for positive integers X and Y. int exp(int…

The following function computes X^Y for positive integers X and Y.

int exp(int X, int Y) {
    int res = 1, a = X, b = Y;
    while (b != 0) {
        if (b % 2 == 0) {
            a = a * a;
            b = b / 2;
        } else {
            res = res * a;
            b = b - 1;
        }
    }
    return res;
}

Which one of the following conditions is TRUE before every iteration of the loop?