projecteuler.net/012/compute_primes.rs

const SIZE: usize  = 1500000;
type Rs = [bool; SIZE + 1];

fn remove_divs(m: usize, xs: &mut Rs) {
    let mut i = m + m;
    while i <= SIZE {
        xs[i] = false;
        i += m;
    }
}

fn get_next_p(m_from: usize, xs: &Rs) -> Option<usize> {
    for k in (m_from + 1)..=SIZE {
       if xs[k] { return Some(k); } 
    }
    return None;
}

fn main() {
    let mut xs: Rs = [true; SIZE + 1];
    let mut q: usize = 1;
    let mut count = 0;
    loop {
        match get_next_p(q, &xs) {
            Some(p) => { 
                q = p; 
                count += 1;
                println!("{}", p);
                if count == 500 { break; }
            }, 
            None => break
        }
        remove_divs(q, &mut xs);
    }
    // println!("[{}]: {}", count, q);
}