code: private int getBondTypes(int idx) {
          int btypes = container.getAtom(idx).getImplicitHydrogenCount();
          for (int end : graph[idx]) {
              IBond bond = edgeToBond.get(idx, end);
              if (bond.getOrder() == SINGLE)
                  btypes += 0x00_0001;
              else if (bond.getOrder() == DOUBLE)
                  btypes += 0x00_0100;
              else // other bond types
                  btypes += 0x01_0000;
          }
          return btypes;
      }
docs: Generate a bond type code for a given atom. The bond code
  can be quickly tested to count the number of single, double,
  or 'other' bonds.
  
  @param idx the atom idx
  @return bond code