// Builds necessary utf8 edges between start & end
 void convertOneEdge(State start, State end, int startCodePoint, int endCodePoint) {
   startUTF8.set(startCodePoint);
   endUTF8.set(endCodePoint);
   // System.out.println("start = " + startUTF8);
   // System.out.println("  end = " + endUTF8);
   build(start, end, startUTF8, endUTF8, 0);
 }
  private void build(
      State start, State end, UTF8Sequence startUTF8, UTF8Sequence endUTF8, int upto) {

    // Break into start, middle, end:
    if (startUTF8.byteAt(upto) == endUTF8.byteAt(upto)) {
      // Degen case: lead with the same byte:
      if (upto == startUTF8.len - 1 && upto == endUTF8.len - 1) {
        // Super degen: just single edge, one UTF8 byte:
        start.addTransition(new Transition(startUTF8.byteAt(upto), endUTF8.byteAt(upto), end));
        return;
      } else {
        assert startUTF8.len > upto + 1;
        assert endUTF8.len > upto + 1;
        State n = newUTF8State();

        // Single value leading edge
        start.addTransition(new Transition(startUTF8.byteAt(upto), n)); // type=single

        // Recurse for the rest
        build(n, end, startUTF8, endUTF8, 1 + upto);
      }
    } else if (startUTF8.len == endUTF8.len) {
      if (upto == startUTF8.len - 1) {
        start.addTransition(
            new Transition(startUTF8.byteAt(upto), endUTF8.byteAt(upto), end)); // type=startend
      } else {
        start(start, end, startUTF8, upto, false);
        if (endUTF8.byteAt(upto) - startUTF8.byteAt(upto) > 1) {
          // There is a middle
          all(
              start,
              end,
              startUTF8.byteAt(upto) + 1,
              endUTF8.byteAt(upto) - 1,
              startUTF8.len - upto - 1);
        }
        end(start, end, endUTF8, upto, false);
      }
    } else {

      // start
      start(start, end, startUTF8, upto, true);

      // possibly middle, spanning multiple num bytes
      int byteCount = 1 + startUTF8.len - upto;
      final int limit = endUTF8.len - upto;
      while (byteCount < limit) {
        // wasteful: we only need first byte, and, we should
        // statically encode this first byte:
        tmpUTF8a.set(startCodes[byteCount - 1]);
        tmpUTF8b.set(endCodes[byteCount - 1]);
        all(start, end, tmpUTF8a.byteAt(0), tmpUTF8b.byteAt(0), tmpUTF8a.len - 1);
        byteCount++;
      }

      // end
      end(start, end, endUTF8, upto, true);
    }
  }