Fast-growing function

/*
A(0,0,0) = 3
A(x,0,0) = 3x+3
A(0,0,z) = A(z,A(0,0,z-1),z-1)
A(x,0,z) = A(x,A(x-1,0,z),z-1)
A(0,y,z) = A(A(0,y-1,z),y-1,z)
A(x,y,z) = A(A(x-1,y,z),y-1,z)
*/

int A(int x, int y, int z) {
    if (x == 0) {
        if (y == 0)  {
            if (z == 0) {
                return 3;
            }
            return A(z, A(0, 0, z - 1), z - 1);
        }
        return A(A(0, y - 1, z), y - 1, z);
    }
    if (y == 0) {
        if (z == 0) {
            return (3 * x) + 3;
        }
        return A(x, A(x - 1, 0, z), z - 1);
    }
    return A(A(x - 1, y, z), y - 1, z);
}