pub fn eq_mask(a: u64, b: u64) -> u64 {
    let x = a ^ b;
    let minus_x = (!x).wrapping_add(1u64);
    let x_or_minus_x = x | minus_x;
    let xnx = x_or_minus_x.wrapping_shr(63);
    xnx.wrapping_sub(1u64)
}

pub fn gte_mask(a: u64, b: u64) -> u64 {
    let x = a;
    let y = b;
    let x_xor_y = x ^ y;
    let x_sub_y = x.wrapping_sub(y);
    let x_sub_y_xor_y = x_sub_y ^ y;
    let q = x_xor_y | x_sub_y_xor_y;
    let x_xor_q = x ^ q;
    let x_xor_q_ = x_xor_q.wrapping_shr(63);
    x_xor_q_.wrapping_sub(1u64)
}