docs: public boolean contains(final long key) {
  
          final int hash  = hashOf(key);
          int index = hash & mask;
          if (contains(key, index)) {
              return true;
          }
  
          if (states[index] == FREE) {
              return false;
          }
  
          int j = index;
          for (int perturb = perturb(hash); states[index] != FREE; perturb >>= PERTURB_SHIFT) {
              j = probe(perturb, j);
              index = j & mask;
              if (contains(key, index)) {
                  return true;
              }
          }
  
          return false;
  
      }