public static int computeIndex(long hash, int indexBitLength)
    {
        return (int) (hash >>> (Long.SIZE - indexBitLength));
    }
@Test
    public void testComputeIndex()
    {
        for (int indexBitLength : new int[] {6, 12, 18}) {
            long index = 5L;
            long hash = index << (Long.SIZE - indexBitLength);
            assertEquals(SfmSketch.computeIndex(hash, indexBitLength), index);
        }
    }