Asriel Camora
65 lines
1.9 KiB
C#
65 lines
1.9 KiB
C#
using System.Diagnostics.Contracts;
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using System.Numerics;
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using System.Runtime.CompilerServices;
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using System.Runtime.Intrinsics;
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using System.Runtime.Intrinsics.X86;
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namespace Craftimizer.Solver.Crafty;
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internal static class Intrinsics
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{
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[Pure]
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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// https://stackoverflow.com/a/73439472
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private static Vector128<float> HMax(Vector256<float> v1)
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{
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var v2 = Avx.Permute(v1, 0b10110001);
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var v3 = Avx.Max(v1, v2);
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var v4 = Avx.Permute(v3, 0b00001010);
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var v5 = Avx.Max(v3, v4);
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var v6 = Avx.ExtractVector128(v5, 1);
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var v7 = Sse.Max(v5.GetLower(), v6);
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return v7;
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}
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[Pure]
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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private static int HMaxIndexScalar(Vector<float> v, int len)
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{
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var m = 0;
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for (var i = 1; i < len; ++i)
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{
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if (v[i] >= v[m])
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m = i;
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}
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return m;
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}
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[Pure]
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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// https://stackoverflow.com/a/23592221
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private static int HMaxIndexAVX2(Vector<float> v, int len)
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{
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// Remove NaNs
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var vfilt = Avx.Blend(v.AsVector256(), Vector256<float>.Zero, (byte)~((1 << len) - 1));
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// Find max value and broadcast to all lanes
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var vmax128 = HMax(vfilt);
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var vmax = Vector256.Create(vmax128, vmax128);
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// Find the highest index with that value, respecting len
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var vcmp = Avx.CompareEqual(vfilt, vmax);
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var mask = unchecked((uint)Avx2.MoveMask(vcmp.AsByte()));
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var inverseIdx = BitOperations.LeadingZeroCount(mask << ((8 - len) << 2)) >> 2;
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return len - 1 - inverseIdx;
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}
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[Pure]
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[MethodImpl(MethodImplOptions.AggressiveInlining)]
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public static int HMaxIndex(Vector<float> v, int len) =>
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Avx2.IsSupported ?
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HMaxIndexAVX2(v, len) :
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HMaxIndexScalar(v, len);
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}
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