docs: private static byte[] expandHrp(final String hrp) {
          int hrpLength = hrp.length();
          byte ret[] = new byte[hrpLength * 2 + 1];
          for (int i = 0; i < hrpLength; ++i) {
              int c = hrp.charAt(i) & 0x7f; // Limit to standard 7-bit ASCII
              ret[i] = (byte) ((c >>> 5) & 0x07);
              ret[i + hrpLength + 1] = (byte) (c & 0x1f);
          }
          ret[hrpLength] = 0;
          return ret;
      }