Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Web/Util/DoubleLinkList.cs

@@ -0,0 +1,114 @@
+//------------------------------------------------------------------------------
+// <copyright file="DoubleLinkList.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>                                                                
+//------------------------------------------------------------------------------
+
+/*
+ * DoubleLinkList
+ * 
+ * Copyright (c) 1998-1999, Microsoft Corporation
+ * 
+ */
+
+namespace System.Web.Util {
+    using System.Text;
+    using System.Runtime.Serialization.Formatters;
+
+    internal class DoubleLinkList : DoubleLink {
+        internal DoubleLinkList() {
+        }
+
+        internal bool IsEmpty() {
+            return _next == this;
+        }
+
+        internal virtual void InsertHead(DoubleLink entry) {
+            entry.InsertAfter(this);
+        }
+        internal virtual void InsertTail(DoubleLink entry) {
+            entry.InsertBefore(this);
+        }
+
+        internal DoubleLinkListEnumerator GetEnumerator() {
+            return new DoubleLinkListEnumerator(this);
+        }
+
+#if DBG
+        internal override void DebugValidate() {
+            DoubleLink  l1, l2;
+
+            base.DebugValidate();
+
+            /*
+             * Detect loops by moving one pointer forward 2 for every 1
+             * of the other.
+             */
+
+            l1 = l2 = this;
+            for (;;) {
+                /* move l2 forward */
+                l2 = l2._next;
+                if (l2 == this)
+                    break;
+
+                Debug.CheckValid(l2 != l1, "Invalid loop in list, first move.");
+                l2.DebugValidate();
+
+                /* move l2 forward again */
+                l2 = l2._next;
+                if (l2 == this)
+                    break;
+
+                Debug.CheckValid(l2 != l1, "Invalid loop in list, second move.");
+                l2.DebugValidate();
+
+                /* move l1 forward */
+                l1 = l1._next;
+            }
+        }
+
+        internal override string DebugDescription(String indent) {
+            string                      desc;
+            DoubleLinkListEnumerator    lenum;
+            int                         c;
+            StringBuilder               sb;
+            string                      i2 = indent + "    ";
+
+            if (IsEmpty()) {
+                desc = indent + "DoubleLinkList is empty\n";
+            }
+            else {
+                c = Length;
+
+                sb = new StringBuilder(indent + "DoubleLinkList has " + c + " entries.\n");
+                lenum = GetEnumerator();
+                while (lenum.MoveNext()) {
+                    sb.Append(Debug.GetDescription(lenum.GetDoubleLink(), i2));
+                }
+
+                desc = sb.ToString();
+            }
+
+            return desc;
+        }
+#endif    
+
+        internal int Length {
+            get {
+                DoubleLinkListEnumerator    lenum;
+                int                         c;
+
+                Debug.Validate(this);
+
+                c = 0;
+                lenum = GetEnumerator();
+                while (lenum.MoveNext()) {
+                    c++;
+                }
+
+                return c;
+            }
+        }
+    }
+}