Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Data.SqlXml/System/Xml/Xsl/Runtime/DodSequenceMerge.cs

@@ -0,0 +1,136 @@
+//------------------------------------------------------------------------------
+// <copyright file="DodSequenceMerge.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>                                                                
+// <owner current="true" primary="true">[....]</owner>
+//------------------------------------------------------------------------------
+using System;
+using System.Collections.Generic;
+using System.Xml.XPath;
+using System.Diagnostics;
+using System.Globalization;
+using System.ComponentModel;
+
+namespace System.Xml.Xsl.Runtime {
+
+    /// <summary>
+    /// Merges several doc-order-distinct sequences into a single doc-order-distinct sequence.
+    /// </summary>
+    [EditorBrowsable(EditorBrowsableState.Never)]
+    public struct DodSequenceMerge {
+        private IList<XPathNavigator> firstSequence;
+        private List<IEnumerator<XPathNavigator>> sequencesToMerge;
+        private int nodeCount;
+        private XmlQueryRuntime runtime;
+
+        /// <summary>
+        /// Initialize this instance of DodSequenceMerge.
+        /// </summary>
+        public void Create(XmlQueryRuntime runtime) {
+            this.firstSequence = null;
+            this.sequencesToMerge = null;
+            this.nodeCount = 0;
+            this.runtime = runtime;
+        }
+
+        /// <summary>
+        /// Add a new sequence to the list of sequences to merge.
+        /// </summary>
+        public void AddSequence(IList<XPathNavigator> sequence) {
+            // Ignore empty sequences
+            if (sequence.Count == 0)
+                return;
+
+            if (this.firstSequence == null) {
+                this.firstSequence = sequence;
+            }
+            else {
+                if (this.sequencesToMerge == null) {
+                    this.sequencesToMerge = new List<IEnumerator<XPathNavigator>>();
+                    MoveAndInsertSequence(this.firstSequence.GetEnumerator());
+                    this.nodeCount = this.firstSequence.Count;
+                }
+
+                MoveAndInsertSequence(sequence.GetEnumerator());
+                this.nodeCount += sequence.Count;
+            }
+        }
+
+        /// <summary>
+        /// Return the fully merged sequence.
+        /// </summary>
+        public IList<XPathNavigator> MergeSequences() {
+            XmlQueryNodeSequence newSequence;
+
+            // Zero sequences to merge
+            if (this.firstSequence == null)
+                return XmlQueryNodeSequence.Empty;
+
+            // One sequence to merge
+            if (this.sequencesToMerge == null || this.sequencesToMerge.Count <= 1)
+                return this.firstSequence;
+
+            // Two or more sequences to merge
+            newSequence = new XmlQueryNodeSequence(this.nodeCount);
+
+            while (this.sequencesToMerge.Count != 1) {
+                // Save last item in list in temp variable, and remove it from list
+                IEnumerator<XPathNavigator> sequence = this.sequencesToMerge[this.sequencesToMerge.Count - 1];
+                this.sequencesToMerge.RemoveAt(this.sequencesToMerge.Count - 1);
+
+                // Add current node to merged sequence
+                newSequence.Add(sequence.Current);
+
+                // Now move to the next node, and re-insert it into the list in reverse document order
+                MoveAndInsertSequence(sequence);
+            }
+
+            // Add nodes in remaining sequence to end of list
+            Debug.Assert(this.sequencesToMerge.Count == 1, "While loop should terminate when count == 1");
+            do {
+                newSequence.Add(this.sequencesToMerge[0].Current);
+            }
+            while (this.sequencesToMerge[0].MoveNext());
+
+            return newSequence;
+        }
+
+        /// <summary>
+        /// Move to the next item in the sequence.  If there is no next item, then do not
+        /// insert the sequence.  Otherwise, call InsertSequence.
+        /// </summary>
+        private void MoveAndInsertSequence(IEnumerator<XPathNavigator> sequence) {
+            if (sequence.MoveNext())
+                InsertSequence(sequence);
+        }
+
+        /// <summary>
+        /// Insert the specified sequence into the list of sequences to be merged.
+        /// Insert it in reverse document order with respect to the current nodes in other sequences.
+        /// </summary>
+        private void InsertSequence(IEnumerator<XPathNavigator> sequence) {
+            for (int i = this.sequencesToMerge.Count - 1; i >= 0; i--) {
+                int cmp = this.runtime.ComparePosition(sequence.Current, this.sequencesToMerge[i].Current);
+
+                if (cmp == -1) {
+                    // Insert after current item
+                    this.sequencesToMerge.Insert(i + 1, sequence);
+                    return;
+                }
+                else if (cmp == 0) {
+                    // Found duplicate, so skip the duplicate
+                    if (!sequence.MoveNext()) {
+                        // No more nodes, so don't insert anything
+                        return;
+                    }
+
+                    // Next node must be after current node in document order, so don't need to reset loop
+                }
+            }
+
+            // Insert at beginning of list
+            this.sequencesToMerge.Insert(0, sequence);
+        }
+    }
+}
+