fn get_nth_zero(val: u8, n: u8) -> u8 {
    let mut num_zs = n + 1;
    let mut bitset = val;
    let mut bitn = 0;
    println!("start loop");
    while num_zs > 0 {
        println!("num_zs {} ", num_zs);

        let trz = (!bitset).trailing_zeros() as u8;

        println!("!bitset = {:08b}, trz = {} bitn = {}", !bitset, trz, bitn);

        bitset >>= trz;
        bitn += trz;

        let trz = (bitset).trailing_zeros() as u8;
        println!(" bitset = {:08b}, trz = {} bitn = {}", bitset, trz, bitn);

        if trz < num_zs {
            bitn += trz;
        } else {
            bitn += num_zs - 1;
            println!();
            break;
        }

        bitset >>= trz;

        num_zs -= trz;
    }
    bitn
}

//#[test]
fn main() {
    assert_eq!(0, get_nth_zero(0, 0));
    assert_eq!(1, get_nth_zero(0b1, 0));
    assert_eq!(6, get_nth_zero(0b00111111, 0));
    assert_eq!(7, get_nth_zero(0b00111111, 1));

    assert_eq!(1, get_nth_zero(0b001111101, 0));
    assert_eq!(7, get_nth_zero(0b001111101, 1));
    assert_eq!(8, get_nth_zero(0b001111101, 2));

    assert_eq!(3, get_nth_zero(0, 3));
}