mirror of https://github.com/ppy/osu
45 lines
1.6 KiB
C#
45 lines
1.6 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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namespace osu.Game.Utils
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{
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/// Provides a fast stateless function that can be used in randomly-looking visual elements.
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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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/// Compute an integer from given seed and series number.
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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 Get(int seed, int series = 0) =>
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unchecked(mix(((ulong)(uint)series << 32) | ((uint)seed ^ 0x12345678)));
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/// Compute a floating point value between 0 and 1 (excluding 1) from given seed and series number.
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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 GetSingle(int seed, int series = 0) =>
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(float)(Get(seed, series) & ((1 << 24) - 1)) / (1 << 24); // float has 24-bit precision
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}
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}
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