System.Xml.Xsl.Runtime.DifferenceIterator.MoveNext C# (CSharp) Method

        public SetIteratorResult MoveNext(XPathNavigator nestedNavigator) {
            switch (this.state) {
                case IteratorState.InitLeft:
                    // Fetched node from left iterator, now get initial node from right iterator
                    this.navLeft = nestedNavigator;
                    this.state = IteratorState.NeedRight;
                    return SetIteratorResult.InitRightIterator;

                case IteratorState.NeedLeft:
                    this.navLeft = nestedNavigator;
                    break;

                case IteratorState.NeedRight:
                    this.navRight = nestedNavigator;
                    break;

                case IteratorState.NeedLeftAndRight:
                    // After fetching left node, still need right node
                    this.navLeft = nestedNavigator;
                    this.state = IteratorState.NeedRight;
                    return SetIteratorResult.NeedRightNode;

                case IteratorState.HaveCurrent:
                    // Just returned left node as current, so fetch new left node
                    Debug.Assert(nestedNavigator == null, "null is passed to MoveNext after IteratorState.HaveCurrent has been returned.");
                    this.state = IteratorState.NeedLeft;
                    return SetIteratorResult.NeedLeftNode;
            }

            if (this.navLeft == null) {
                // If navLeft is null, then difference operation is complete
                return SetIteratorResult.NoMoreNodes;
            }
            else if (this.navRight != null) {
                int order = this.runtime.ComparePosition(this.navLeft, this.navRight);

                // If navLeft is positioned to same node as navRight,
                if (order == 0) {
                    // Skip navLeft and navRight
                    this.state = IteratorState.NeedLeftAndRight;
                    return SetIteratorResult.NeedLeftNode;
                }

                // If navLeft is after navRight in document order, then skip navRight
                if (order > 0) {
                    this.state = IteratorState.NeedRight;
                    return SetIteratorResult.NeedRightNode;
                }
            }

            // Return navLeft
            this.state = IteratorState.HaveCurrent;
            return SetIteratorResult.HaveCurrentNode;
        }