61 lines
1.8 KiB
C#
61 lines
1.8 KiB
C#
// Licensed to the .NET Foundation under one or more agreements.
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// The .NET Foundation licenses this file to you under the MIT license.
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// See the LICENSE file in the project root for more information.
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#if !NET6_0_OR_GREATER
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using System.Runtime.CompilerServices;
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#if NETCOREAPP3_1
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using System.Runtime.Intrinsics.X86;
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using static System.Numerics.BitOperations;
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#endif
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namespace CommunityToolkit.HighPerformance.Helpers.Internals;
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/// <summary>
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/// Utility methods for intrinsic bit-twiddling operations. The methods use hardware intrinsics
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/// when available on the underlying platform, otherwise they use optimized software fallbacks.
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/// </summary>
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internal static class BitOperations
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{
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/// <summary>
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/// Round the given integral value up to a power of 2.
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/// </summary>
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/// <param name="value">The value.</param>
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/// <returns>
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/// The smallest power of 2 which is greater than or equal to <paramref name="value"/>.
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/// If <paramref name="value"/> is 0 or the result overflows, returns 0.
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/// </returns>
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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public static unsafe uint RoundUpToPowerOf2(uint value)
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{
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#if NETCOREAPP3_1
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if (Lzcnt.IsSupported)
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{
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if (sizeof(nint) == 8)
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{
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return (uint)(0x1_0000_0000ul >> LeadingZeroCount(value - 1));
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}
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else
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{
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int shift = 32 - LeadingZeroCount(value - 1);
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return (1u ^ (uint)(shift >> 5)) << shift;
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}
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}
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#endif
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// Based on https://graphics.stanford.edu/~seander/bithacks.html#RoundUpPowerOf2
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--value;
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value |= value >> 1;
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value |= value >> 2;
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value |= value >> 4;
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value |= value >> 8;
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value |= value >> 16;
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return value + 1;
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}
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}
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#endif
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