mirror of
https://github.com/ppy/osu
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92 lines
3.2 KiB
C#
92 lines
3.2 KiB
C#
// Copyright (c) 2007-2018 ppy Pty Ltd <contact@ppy.sh>.
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// Licensed under the MIT Licence - https://raw.githubusercontent.com/ppy/osu/master/LICENCE
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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 uint_to_real = 1.0 / (uint.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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private uint _x, _y = y, _z = z, _w = 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() => uint_to_real * NextUInt();
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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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