static int compareUtf8(byte[] left, byte[] right) {
  int n = min(left.length, right.length);
  for (int i = 0; i < n; i++) {
    int a = left[i] & 0xff;
    int b = right[i] & 0xff;
    if (a != b) ret a-b;
  }
  ret left.length - right.length;
}