code: Item newDouble(final double value) {
          key.set(value);
          Item result = get(key);
          if (result == null) {
              pool.putByte(DOUBLE).putLong(key.longVal);
              result = new Item(index, key);
              put(result);
              index += 2;
          }
          return result;
      }
docs: Adds a double to the constant pool of the class being build. Does nothing
  if the constant pool already contains a similar item.
  
  @param value the double value.
  @return a new or already existing double item.