Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

mcs/class/referencesource/System.Xml/System/Xml/HWStack.cs

@@ -0,0 +1,111 @@
+//------------------------------------------------------------------------------
+// <copyright file="HWStack.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>
+// <owner current="true" primary="true">[....]</owner>
+//------------------------------------------------------------------------------
+
+using System;
+
+
+namespace System.Xml {
+
+// This stack is designed to minimize object creation for the
+// objects being stored in the stack by allowing them to be
+// re-used over time.  It basically pushes the objects creating
+// a high water mark then as Pop() is called they are not removed
+// so that next time Push() is called it simply returns the last
+// object that was already on the stack.
+
+    internal class HWStack : ICloneable {
+        internal HWStack(int GrowthRate) : this (GrowthRate, int.MaxValue) {}
+
+        internal HWStack(int GrowthRate, int limit) {
+            this.growthRate = GrowthRate;
+            this.used = 0;
+            this.stack = new Object[GrowthRate];
+            this.size = GrowthRate;
+            this.limit = limit;
+        }
+
+        internal Object Push() {
+            if (this.used == this.size) {
+                if (this.limit <= this.used) {
+                    throw new XmlException(Res.Xml_StackOverflow, string.Empty);
+                }
+                Object[] newstack = new Object[this.size + this.growthRate];
+                if (this.used > 0) {
+                    System.Array.Copy(this.stack, 0, newstack, 0, this.used);
+                }
+                this.stack = newstack;
+                this.size += this.growthRate;
+            }
+            return this.stack[this.used++];
+        }
+
+        internal Object Pop() {
+            if (0 < this.used) {
+                this.used--;
+                Object result = this.stack[this.used];
+                return result;
+            }
+            return null;
+        }
+
+        internal object Peek() {
+            return this.used > 0 ? this.stack[this.used - 1] : null;
+        }
+
+        internal void AddToTop(object o) {
+            if (this.used > 0) {
+                this.stack[this.used - 1] = o;
+            }
+        }
+
+        internal Object this[int index] {
+            get {
+                if (index >= 0 && index < this.used) {
+                    Object result = this.stack[index];
+                    return result;
+                }
+                else {
+					throw new IndexOutOfRangeException();
+				}
+            }
+            set {
+                if (index >= 0 && index < this.used) {
+					this.stack[index] = value;
+				}
+                else {
+					throw new IndexOutOfRangeException();
+				}
+            }
+        }
+
+        internal int Length {
+            get { return this.used;}
+        }
+
+        //
+        // ICloneable
+        //
+
+        private HWStack(object[] stack, int growthRate, int used, int size) {
+            this.stack      = stack;
+            this.growthRate = growthRate;
+            this.used       = used;
+            this.size       = size;
+        }
+
+        public object Clone() {
+            return new HWStack((object[]) this.stack.Clone(), this.growthRate, this.used, this.size);
+        }
+
+        private Object[] stack;
+        private int growthRate;
+        private int used;
+        private int size;
+        private int limit;
+    };
+
+}