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85 lines
3.0 KiB
C#
85 lines
3.0 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.Utils
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{
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/// <summary>
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/// Provides a fast stateless function that can be used in randomly-looking visual elements.
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/// </summary>
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public static class StatelessRNG
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{
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private static ulong mix(ulong x)
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{
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unchecked
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{
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x ^= x >> 33;
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x *= 0xff51afd7ed558ccd;
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x ^= x >> 33;
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x *= 0xc4ceb9fe1a85ec53;
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x ^= x >> 33;
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return x;
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}
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}
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/// <summary>
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/// Generate a random 64-bit unsigned integer from given seed.
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/// </summary>
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/// <param name="seed">
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/// The seed value of this random number generator.
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/// </param>
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/// <param name="series">
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/// The series number.
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/// Different values are computed for the same seed in different series.
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/// </param>
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public static ulong NextULong(int seed, int series = 0)
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{
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unchecked
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{
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ulong combined = ((ulong)(uint)series << 32) | (uint)seed;
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// The xor operation is to not map (0, 0) to 0.
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return mix(combined ^ 0x12345678);
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}
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}
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/// <summary>
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/// Generate a random integer in range [0, maxValue) from given seed.
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/// </summary>
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/// <param name="maxValue">
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/// The number of possible results.
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/// </param>
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/// <param name="seed">
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/// The seed value of this random number generator.
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/// </param>
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/// <param name="series">
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/// The series number.
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/// Different values are computed for the same seed in different series.
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/// </param>
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public static int NextInt(int maxValue, int seed, int series = 0)
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{
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ArgumentOutOfRangeException.ThrowIfNegativeOrZero(maxValue);
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return (int)(NextULong(seed, series) % (ulong)maxValue);
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}
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/// <summary>
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/// Compute a random floating point value between 0 and 1 (excluding 1) from given seed and series number.
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/// </summary>
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/// <param name="seed">
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/// The seed value of this random number generator.
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/// </param>
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/// <param name="series">
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/// The series number.
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/// Different values are computed for the same seed in different series.
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/// </param>
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public static float NextSingle(int seed, int series = 0) =>
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(float)(NextULong(seed, series) & ((1 << 24) - 1)) / (1 << 24); // float has 24-bit precision
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/// <summary>
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/// Compute a random floating point value between <paramref name="min"/> and <paramref name="max"/> from given seed and series number.
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/// </summary>
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public static float NextSingle(float min, float max, int seed, int series = 0) => min + NextSingle(seed, series) * (max - min);
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}
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}
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