code: public static int mixHashCodes(int hash1, int hash2, int hash3) {
      long result = hash1 * HASHPRIME + hash2;
      return (int) (result * HASHPRIME + hash3);
    }
docs: Mix multiple hashcodes into one.
  
  @param hash1 First hashcode to mix
  @param hash2 Second hashcode to mix
  @param hash3 Third hashcode to mix
  @return Mixed hash code