docs: public boolean add(long key) {
          final int index = ((((int) (key >>> 32)) ^ ((int) (key))) & 0x7fffffff) % capacity;
          final Entry entryOriginal = table[index];
          for (Entry entry = entryOriginal; entry != null; entry = entry.next) {
              if (entry.key == key) {
                  return false;
              }
          }
          table[index] = new Entry(key, entryOriginal);
          size++;
          if (size > threshold) {
              setCapacity(2 * capacity);
          }
          return true;
      }