osu/osu.Game.Rulesets.Mania/MathUtils/FastRandom.cs

92 lines
3.1 KiB
C#

// 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.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;
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;
}
}
}