// 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; namespace osu.Game.Rulesets.Mania.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; internal uint X { get; private set; } internal uint Y { get; private set; } = y; internal uint Z { get; private set; } = z; internal uint W { get; private set; } = 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; } } }