checkNonnegative(oldCount, "oldCount");
    checkNonnegative(newCount, "newCount");
    int entryIndex = backingMap.indexOf(element);
    if (entryIndex == -1) {
      if (oldCount != 0) {
        return false;
      }
      if (newCount > 0) {
        backingMap.put(element, newCount);
        size += newCount;
      }
      return true;
    }

  public boolean setCount(@ParametricNullness E element, int oldCount, int newCount) {
    checkNonnegative(newCount, "newCount");
    checkNonnegative(oldCount, "oldCount");
    checkArgument(range.contains(element));

    AvlNode<E> root = rootReference.get();
    if (root == null) {
      if (oldCount == 0) {
        if (newCount > 0) {
          add(element, newCount);
        }
        return true;
      } else {

  public boolean setCount(@ParametricNullness E element, int oldCount, int newCount) {
    checkNonnegative(newCount, "newCount");
    checkNonnegative(oldCount, "oldCount");
    checkArgument(range.contains(element));

    AvlNode<E> root = rootReference.get();
    if (root == null) {
      if (oldCount == 0) {
        if (newCount > 0) {
          add(element, newCount);
        }
        return true;
      } else {

    AtomicInteger existingCounter = safeGet(countMap, element);
    if (existingCounter == null) {
      if (expectedOldCount != 0) {
        return false;
      } else if (newCount == 0) {
        return true;
      } else {
        // if our write lost the race, it must have lost to a nonzero value, so we can stop
        return countMap.putIfAbsent(element, new AtomicInteger(newCount)) == null;

      count += values.length();
      return this;
    }

    private void ensureRoomFor(int numberToAdd) {
      int newCount = count + numberToAdd; // TODO(kevinb): check overflow now?
      if (newCount > array.length) {
        array = Arrays.copyOf(array, expandedCapacity(array.length, newCount));
      }
    }

    // Unfortunately this is pasted from ImmutableCollection.Builder.

      count += values.length();
      return this;
    }

    private void ensureRoomFor(int numberToAdd) {
      int newCount = count + numberToAdd; // TODO(kevinb): check overflow now?
      if (newCount > array.length) {
        array = Arrays.copyOf(array, expandedCapacity(array.length, newCount));
      }
    }

    // Unfortunately this is pasted from ImmutableCollection.Builder.