Imported Upstream version 5.20.0.208

Former-commit-id: 8fbf7dae6cd486bffb1fa6a52020e8eb23c570b1

external/cecil/Mono/MergeSort.cs

@@ -0,0 +1,66 @@
+//
+// Author:
+//   Jb Evain (jbevain@gmail.com)
+//
+// Copyright (c) 2008 - 2015 Jb Evain
+// Copyright (c) 2008 - 2011 Novell, Inc.
+//
+// Licensed under the MIT/X11 license.
+//
+
+using System;
+using System.Collections.Generic;
+
+namespace Mono {
+
+	class MergeSort<T> {
+		private readonly T [] elements;
+		private readonly T [] buffer;
+		private readonly IComparer<T> comparer;
+
+		private MergeSort (T [] elements, IComparer<T> comparer)
+		{
+			this.elements = elements;
+			this.buffer = new T [elements.Length];
+			Array.Copy (this.elements, this.buffer, elements.Length);
+			this.comparer = comparer;
+		}
+
+		public static void Sort (T [] source, IComparer<T> comparer)
+		{
+			Sort (source, 0, source.Length, comparer);
+		}
+
+		public static void Sort (T [] source, int start, int length, IComparer<T> comparer)
+		{
+			new MergeSort<T> (source, comparer).Sort (start, length);
+		}
+
+		private void Sort (int start, int length)
+		{
+			TopDownSplitMerge (this.buffer, this.elements, start, length);
+		}
+
+		private void TopDownSplitMerge (T [] a, T [] b, int start, int end)
+		{
+			if (end - start < 2)
+				return;
+
+			int middle = (end + start) / 2;
+			TopDownSplitMerge (b, a, start, middle);
+			TopDownSplitMerge (b, a, middle, end);
+			TopDownMerge (a, b, start, middle, end);
+		}
+
+		private void TopDownMerge (T [] a, T [] b, int start, int middle, int end)
+		{
+			for (int i = start, j = middle, k = start; k < end; k++) {
+				if (i < middle && (j >= end || comparer.Compare (a [i], a [j]) <= 0)) {
+					b [k] = a [i++];
+				} else {
+					b [k] = a [j++];
+				}
+			}
+		}
+	}
+}