Rust Sieve of Eratosthenes

prime_sieve.rs

// Find all prime numbers less than n
fn small_primes(bound: uint) -> ~[uint] {
  // num is considered prime as long as primes[num] is true
  // Start with all evens besides 2 filtered out
  let mut primes = std::vec::from_fn(bound+1, |num| num == 2 || num & 1 != 0);

  // Start at 3 and step by 2 because we've already filtered multiples of 2
  for num in count(3u, 2).filter(|&num| primes[num]).take_while(|&num| num * num <= bound) {
    // Mark prime num's multiples non-prime
    // We can start at num^2 because smaller non-primes have already been eliminated
    for j in range_step_inclusive(num*num, bound, num) { primes[j] = false; }
  }

  primes.
    move_iter().
    enumerate().
    skip(2).
    filter_map(|(i, p)| if p {Some(i)} else {None}).
    collect::<~[uint]>()
}

#[test]
fn test_small_primes() {
  assert_eq!(small_primes(20), ~[2, 3, 5, 7, 11, 13, 17, 19]);
}

A version that works with Rust v1+: https://gist.github.com/glebm/440bbe2fc95e7abee40eb260ec82f85c