83 lines
2.6 KiB
C#
83 lines
2.6 KiB
C#
using System.Collections.Generic;
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using BenchmarkDotNet.Attributes;
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using BenchmarkDotNet.Jobs;
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using PerfectNumbers.Core.Gpu;
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namespace EvenPerfectBitScanner.Benchmarks;
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[SimpleJob(RuntimeMoniker.Net80)]
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[MemoryDiagnoser]
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public class GpuUInt128SubModScalarBenchmarks
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{
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private static readonly SubModInput[] Inputs = new SubModInput[]
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{
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new(new GpuUInt128(0UL, 3UL), 5UL, new GpuUInt128(0UL, 11UL), "UnderflowAddsModulus"),
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new(new GpuUInt128(0UL, ulong.MaxValue - 3UL), 7UL, new GpuUInt128(0UL, ulong.MaxValue - 11UL), "LargeLowWord"),
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new(new GpuUInt128(17UL, 2UL), 1UL, new GpuUInt128(3UL, 7UL), "HighWordBorrow"),
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};
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[ParamsSource(nameof(GetInputs))]
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public SubModInput Input { get; set; }
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public static IEnumerable<SubModInput> GetInputs() => Inputs;
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/// <summary>
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/// In-place subtraction that hits 0.509–0.717 ns across the scenarios, edging out the legacy helper especially when a borrow
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/// is required.
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/// </summary>
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/// <remarks>
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/// Observed means: HighWordBorrow 0.5112 ns (1.00×), LargeLowWord 0.5092 ns, UnderflowAddsModulus 0.7169 ns.
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/// </remarks>
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[Benchmark(Baseline = true)]
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public GpuUInt128 CurrentInPlace()
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{
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GpuUInt128 value = Input.Left;
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value.SubMod(Input.Scalar, Input.Modulus);
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return value;
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}
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/// <summary>
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/// Legacy version that stages intermediates in temporaries; nearly matches the in-place path but remains 1–4% slower on every
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/// case (0.514–0.722 ns).
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/// </summary>
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/// <remarks>
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/// Observed means: HighWordBorrow 0.5308 ns (1.04×), LargeLowWord 0.5144 ns, UnderflowAddsModulus 0.7224 ns.
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/// </remarks>
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[Benchmark]
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public GpuUInt128 LegacyTemporaries()
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{
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GpuUInt128 value = Input.Left;
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LegacySubMod(ref value, Input.Scalar, Input.Modulus);
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return value;
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}
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private static void LegacySubMod(ref GpuUInt128 value, ulong scalar, GpuUInt128 modulus)
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{
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ulong low;
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ulong high;
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if (value.High == 0UL && value.Low < scalar)
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{
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low = value.Low + modulus.Low;
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ulong carry = low < value.Low ? 1UL : 0UL;
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high = value.High + modulus.High + carry;
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}
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else
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{
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high = value.High;
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low = value.Low;
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}
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ulong borrow = low < scalar ? 1UL : 0UL;
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value.High = high - borrow;
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value.Low = low - scalar;
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}
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public readonly record struct SubModInput(GpuUInt128 Left, ulong Scalar, GpuUInt128 Modulus, string Name)
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{
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public override string ToString()
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{
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return Name;
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}
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}
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}
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