* @param m total number of bits in Bloom filter (must be positive)
   */
  @VisibleForTesting
  static int optimalNumOfHashFunctions(long n, long m) {
    // (m / n) * log(2), but avoid truncation due to division!
    return Math.max(1, (int) Math.round((double) m / n * Math.log(2)));
  }

  /**
   * Computes m (total bits of Bloom filter) which is expected to achieve, for the specified