BN_is_even
while (BN_is_even(&u) == 1) {
while (BN_is_even(&v) == 1) {
if (BN_is_even(&x) == 1 && BN_is_even(&y) == 1) {
while (BN_is_even(&u) == 1) {
while (BN_is_even(&v) == 1) {