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96 lines
3.2 KiB
C#
96 lines
3.2 KiB
C#
// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
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// See the LICENCE file in the repository root for full licence text.
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using System;
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namespace osu.Game.Rulesets.Mania.MathUtils
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{
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/// <summary>
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/// A PRNG specified in http://heliosphan.org/fastrandom.html.
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/// </summary>
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internal class FastRandom
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{
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private const double int_to_real = 1.0 / (int.MaxValue + 1.0);
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private const uint int_mask = 0x7FFFFFFF;
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private const uint y = 842502087;
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private const uint z = 3579807591;
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private const uint w = 273326509;
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internal uint X { get; private set; }
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internal uint Y { get; private set; } = y;
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internal uint Z { get; private set; } = z;
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internal uint W { get; private set; } = w;
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public FastRandom(int seed)
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{
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X = (uint)seed;
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}
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public FastRandom()
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: this(Environment.TickCount)
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{
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}
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/// <summary>
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/// Generates a random unsigned integer within the range [<see cref="uint.MinValue"/>, <see cref="uint.MaxValue"/>).
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/// </summary>
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/// <returns>The random value.</returns>
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public uint NextUInt()
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{
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uint t = X ^ (X << 11);
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X = Y;
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Y = Z;
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Z = W;
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return W = W ^ (W >> 19) ^ t ^ (t >> 8);
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}
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/// <summary>
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/// Generates a random integer value within the range [0, <see cref="int.MaxValue"/>).
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/// </summary>
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/// <returns>The random value.</returns>
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public int Next() => (int)(int_mask & NextUInt());
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/// <summary>
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/// Generates a random integer value within the range [0, <paramref name="upperBound"/>).
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/// </summary>
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/// <param name="upperBound">The upper bound.</param>
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/// <returns>The random value.</returns>
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public int Next(int upperBound) => (int)(NextDouble() * upperBound);
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/// <summary>
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/// Generates a random integer value within the range [<paramref name="lowerBound"/>, <paramref name="upperBound"/>).
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/// </summary>
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/// <param name="lowerBound">The lower bound of the range.</param>
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/// <param name="upperBound">The upper bound of the range.</param>
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/// <returns>The random value.</returns>
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public int Next(int lowerBound, int upperBound) => (int)(lowerBound + NextDouble() * (upperBound - lowerBound));
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/// <summary>
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/// Generates a random double value within the range [0, 1).
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/// </summary>
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/// <returns>The random value.</returns>
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public double NextDouble() => int_to_real * Next();
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private uint bitBuffer;
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private int bitIndex = 32;
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/// <summary>
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/// Generates a reandom boolean value. Cached such that a random value is only generated once in every 32 calls.
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/// </summary>
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/// <returns>The random value.</returns>
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public bool NextBool()
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{
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if (bitIndex == 32)
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{
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bitBuffer = NextUInt();
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bitIndex = 1;
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return (bitBuffer & 1) == 1;
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}
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bitIndex++;
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return ((bitBuffer >>= 1) & 1) == 1;
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}
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}
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}
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