code: public static int count_2(int[] buffer, int n) {
  		final int n1 = n - n % 48;
  		final int n2 = n - n % 6;
  
  		int cnt = 0;
  		int i;
  		for (i = 0; i < n1; i += 48)
  			cnt += merging3_2(buffer, i);
  		for (; i < n2; i += 6)
  			cnt += merging2_2(buffer, i);
  		cnt += popcount_fbsd2_2(buffer, i, n);
  		return cnt;
  	}
docs: Population count, skipping words at even positions
  <p>
  It counts 24 words at a time, then 3 at a time, then 1 at a time
  
  @param buffer
  array of <code>int</code>
  @param n
  number of elements of <code>buffer</code> to count
  @return population count