code: public FP64 extend(String s) {
      final int len = s.length();
      for (int i = 0; i < len; i++) {
        extend(s.charAt(i));
      }
      return this;
    }
docs: Extends this fingerprint by the characters of the String
  <code>s</code>, which must be non-null.
  
  @return
  the resulting fingerprint.