// returns index of most significant '1' bit in a number
pub fn msb_idx(b: u64) -> u8 {
    let mut idx: u8 = 0;
    let mut tmp: u64 = b;

    while tmp != 0 {
        tmp >>= 1;
        idx += 1;
    }
    idx - 1
}

// returns index of the least significant '1' bit in a number
pub fn lsb_idx(b: u64) -> u8 {
    let lsb: u64 = b ^ (b & (b - 1));  // isolate the LSB
    msb_idx(lsb)  // the isolated LSB is now also the MSB
}