rename OpenRA.Support.Random aka XRandom to MersenneTwister

OpenRA.Game/Support/MersenneTwister.cs

@@ -0,0 +1,67 @@
+#region Copyright & License Information
+/*
+ * Copyright 2007-2014 The OpenRA Developers (see AUTHORS)
+ * This file is part of OpenRA, which is free software. It is made
+ * available to you under the terms of the GNU General Public License
+ * as published by the Free Software Foundation. For more information,
+ * see COPYING.
+ */
+#endregion
+
+using System;
+
+namespace OpenRA.Support
+{
+	// quick & dirty Mersenne Twister [MT19937] implementation
+	public class MersenneTwister
+	{
+		uint[] mt = new uint[624];
+		int index = 0;
+
+		public int Last;
+		public int TotalCount = 0;
+
+		public MersenneTwister() : this(Environment.TickCount) { }
+
+		public MersenneTwister(int seed)
+		{
+			mt[0] = (uint)seed;
+			for (var i = 1u; i < mt.Length; i++)
+				mt[i] = 1812433253u * (mt[i - 1] ^ (mt[i - 1] >> 30)) + i;
+		}
+
+		public int Next()
+		{
+			if (index == 0) Generate();
+
+			var y = mt[index];
+			y ^= (y >> 11);
+			y ^= ((y << 7) & 2636928640);
+			y ^= ((y << 15) & 4022730752);
+			y ^= y >> 18;
+
+			index = (index + 1) % 624;
+			TotalCount++;
+			Last = (int)(y % int.MaxValue);
+			return Last;
+		}
+
+		public int Next(int low, int high) { return low + Next() % (high - low); }
+		public int Next(int high) { return Next() % high; }
+		public float NextFloat() { return Math.Abs(Next() / (float)0x7fffffff); }
+
+		void Generate()
+		{
+			unchecked
+			{
+				for (var i = 0u; i < mt.Length; i++)
+				{
+					var y = (mt[i] & 0x80000000) | (mt[(i + 1) % 624] & 0x7fffffff);
+					mt[i] = mt[(i + 397u) % 624u] ^ (y >> 1);
+					if ((y & 1) == 1)
+						mt[i] = (mt[i] ^ 2567483615);
+				}
+			}
+		}
+	}
+}