let b2 = BigInt::from_vec(vec![0, 1]);
assert_eq!(&b1 + &b2, BigInt::from_vec(vec![1 << 32, 1]));
let b2 = BigInt::from_vec(vec![0, 1]);
assert_eq!(&b1 + &b2, BigInt::from_vec(vec![1 << 32, 1]));
// For example, you may want to return an `Option`, to panic, or to return `0`.
// For example, you may want to return an `Option`, to panic, or to return `0`.