code: protected final int keyToIndex (int key)
      {
          // we lift the hash-fixing function from HashMap because Sun
          // wasn't kind enough to make it public
          key += ~(key << 9);
          key ^=  (key >>> 14);
          key +=  (key << 4);
          key ^=  (key >>> 10);
          return key & (_buckets.length - 1);
      }
docs: Turn the specified key into an index.