docs: public static byte[] longToUID(final long uid, final short width) {
      // Verify that we're going to drop bytes that are 0.
      final byte[] padded = Bytes.fromLong(uid);
      for (int i = 0; i < padded.length - width; i++) {
        if (padded[i] != 0) {
          final String message = "UID " + Long.toString(uid) + 
            " was too large for " + width + " bytes";
          LOG.error("OMG " + message);
          throw new IllegalStateException(message);
        }
      }
      // Shrink the ID on the requested number of bytes.
      return Arrays.copyOfRange(padded, padded.length - width, padded.length);
    }