From ca2c2097016521c16a345e6a173d4e62c78cac0a Mon Sep 17 00:00:00 2001
From: ekrctb <ekrctb@gmail.com>
Date: Fri, 25 May 2018 16:26:19 +0900
Subject: [PATCH] add FastRandom

---
 .../MathUtils/FastRandom.cs                   | 91 +++++++++++++++++++
 1 file changed, 91 insertions(+)
 create mode 100644 osu.Game.Rulesets.Catch/MathUtils/FastRandom.cs

diff --git a/osu.Game.Rulesets.Catch/MathUtils/FastRandom.cs b/osu.Game.Rulesets.Catch/MathUtils/FastRandom.cs
new file mode 100644
index 0000000000..5e8256a504
--- /dev/null
+++ b/osu.Game.Rulesets.Catch/MathUtils/FastRandom.cs
@@ -0,0 +1,91 @@
+// Copyright (c) 2007-2018 ppy Pty Ltd <contact@ppy.sh>.
+// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
+
+using System;
+
+namespace osu.Game.Rulesets.Catch.MathUtils
+{
+    /// <summary>
+    /// A PRNG specified in http://heliosphan.org/fastrandom.html.
+    /// </summary>
+    internal class FastRandom
+    {
+        private const double int_to_real = 1.0 / (int.MaxValue + 1.0);
+        private const uint int_mask = 0x7FFFFFFF;
+        private const uint y = 842502087;
+        private const uint z = 3579807591;
+        private const uint w = 273326509;
+        private uint _x, _y = y, _z = z, _w = w;
+
+        public FastRandom(int seed)
+        {
+            _x = (uint)seed;
+        }
+
+        public FastRandom()
+            : this(Environment.TickCount)
+        {
+        }
+
+        /// <summary>
+        /// Generates a random unsigned integer within the range [<see cref="uint.MinValue"/>, <see cref="uint.MaxValue"/>).
+        /// </summary>
+        /// <returns>The random value.</returns>
+        public uint NextUInt()
+        {
+            uint t = _x ^ _x << 11;
+            _x = _y;
+            _y = _z;
+            _z = _w;
+            return _w = _w ^ _w >> 19 ^ t ^ t >> 8;
+        }
+
+        /// <summary>
+        /// Generates a random integer value within the range [0, <see cref="int.MaxValue"/>).
+        /// </summary>
+        /// <returns>The random value.</returns>
+        public int Next() => (int)(int_mask & NextUInt());
+
+        /// <summary>
+        /// Generates a random integer value within the range [0, <paramref name="upperBound"/>).
+        /// </summary>
+        /// <param name="upperBound">The upper bound.</param>
+        /// <returns>The random value.</returns>
+        public int Next(int upperBound) => (int)(NextDouble() * upperBound);
+
+        /// <summary>
+        /// Generates a random integer value within the range [<paramref name="lowerBound"/>, <paramref name="upperBound"/>).
+        /// </summary>
+        /// <param name="lowerBound">The lower bound of the range.</param>
+        /// <param name="upperBound">The upper bound of the range.</param>
+        /// <returns>The random value.</returns>
+        public int Next(int lowerBound, int upperBound) => (int)(lowerBound + NextDouble() * (upperBound - lowerBound));
+
+        /// <summary>
+        /// Generates a random double value within the range [0, 1).
+        /// </summary>
+        /// <returns>The random value.</returns>
+        public double NextDouble() => int_to_real * Next();
+
+        private uint bitBuffer;
+        private int bitIndex = 32;
+
+        /// <summary>
+        /// Generates a reandom boolean value. Cached such that a random value is only generated once in every 32 calls.
+        /// </summary>
+        /// <returns>The random value.</returns>
+        public bool NextBool()
+        {
+            if (bitIndex == 32)
+            {
+                bitBuffer = NextUInt();
+                bitIndex = 1;
+
+                return (bitBuffer & 1) == 1;
+            }
+
+            bitIndex++;
+            return ((bitBuffer >>= 1) & 1) == 1;
+        }
+    }
+}