Move FastRandom to LegacyRandom in osu.Game project

osu.Game/Utils/LegacyRandom.cs

@@ -0,0 +1,108 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+using osu.Framework.Utils;
+
+namespace osu.Game.Utils
+{
+    /// <summary>
+    /// A PRNG specified in http://heliosphan.org/fastrandom.html.
+    /// Should only be used to match legacy behaviour. See <see cref="RNG"/> for a newer alternative.
+    /// </summary>
+    /// <remarks>
+    /// Known in osu-stable code as `FastRandom`.
+    /// </remarks>
+    public class LegacyRandom
+    {
+        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;
+
+        public uint X { get; private set; }
+        public uint Y { get; private set; } = y;
+        public uint Z { get; private set; } = z;
+        public uint W { get; private set; } = w;
+
+        public LegacyRandom(int seed)
+        {
+            X = (uint)seed;
+        }
+
+        public LegacyRandom()
+            : 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 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(double lowerBound, double 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;
+        }
+    }
+}