even-perfect-numbers-scanner/PerfectNumbers.Core/PrimeTester.cs

using System.Buffers;
using System.Collections.Concurrent;
using System.Numerics;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using ILGPU;
using ILGPU.Runtime;
using PerfectNumbers.Core.Gpu;

namespace PerfectNumbers.Core;

public sealed class PrimeTester
{
	public PrimeTester()
	{
	}

	[ThreadStatic]
	private static PrimeTester? _tester;

	public static PrimeTester Exclusive => _tester ??= new();

	public static bool IsPrime(ulong n)
	{
		if (n <= 1UL)
		{
			return false;
		}

		if (n == 2UL)
		{
			throw new InvalidOperationException("PrimeTester.IsPrime encountered the sentinel input 2.");
		}

		bool isOdd = (n & 1UL) != 0UL;
		bool result = isOdd;

		bool requiresTrialDivision = result && n >= 7UL;

		if (requiresTrialDivision)
		{
			// EvenPerfectBitScanner streams exponents starting at 136,279,841, so the Mod10/GCD guard never fires on the
			// production path. Leave the logic commented out as instrumentation for diagnostic builds.
			// bool sharesMaxExponentFactor = n.Mod10() == 1UL && SharesFactorWithMaxExponent(n);
			// result &= !sharesMaxExponentFactor;

			if (result)
			{
				uint[] smallPrimeDivisors = PrimesGenerator.SmallPrimes;
				ulong[] smallPrimeDivisorsMul = PrimesGenerator.SmallPrimesPow2;

				ulong nMod10 = n.Mod10();
				switch (nMod10)
				{
					case 1UL:
						smallPrimeDivisors = PrimesGenerator.SmallPrimesLastOne;
						smallPrimeDivisorsMul = PrimesGenerator.SmallPrimesPow2LastOne;
						break;
					case 3UL:
						smallPrimeDivisors = DivisorGenerator.SmallPrimesLastThree;
						smallPrimeDivisorsMul = DivisorGenerator.SmallPrimesPow2LastThree;
						break;
					case 7UL:
						smallPrimeDivisors = PrimesGenerator.SmallPrimesLastSeven;
						smallPrimeDivisorsMul = PrimesGenerator.SmallPrimesPow2LastSeven;
						break;
					case 9UL:
						smallPrimeDivisors = DivisorGenerator.SmallPrimesLastNine;
						smallPrimeDivisorsMul = DivisorGenerator.SmallPrimesPow2LastNine;
						break;
				}

				int smallPrimeDivisorsLength = smallPrimeDivisors.Length;
				for (int i = 0; i < smallPrimeDivisorsLength; i++)
				{
					if (smallPrimeDivisorsMul[i] > n)
					{
						break;
					}

					if (n % smallPrimeDivisors[i] == 0)
					{
						result = false;
						break;
					}
				}
			}
		}

		return result;
	}

	[MethodImpl(MethodImplOptions.AggressiveInlining)]
	public bool IsPrimeGpu(ulong n)
	{
		bool forceCpu = GpuContextPool.ForceCpu;
		bool belowGpuRange = n < 31UL;

		if (forceCpu || belowGpuRange)
		{
			return IsPrime(n);
		}

		var limiter = GpuPrimeWorkLimiter.Acquire();
		var gpu = PrimeTesterGpuContextPool.Rent(1);
		var accelerator = gpu.Accelerator;
		var kernel = gpu.Kernel;

		ulong value = n;
		byte flag = 0;

		var input = gpu.Input;
		var output = gpu.Output;
		var inputView = input.View;
		var outputView = output.View;

		inputView.CopyFromCPU(ref value, 1);
		kernel(
						1,
						inputView,
						gpu.DevicePrimesDefault.View,
						gpu.DevicePrimesLastOne.View,
						gpu.DevicePrimesLastSeven.View,
						gpu.DevicePrimesLastThree.View,
						gpu.DevicePrimesLastNine.View,
						gpu.DevicePrimesPow2Default.View,
						gpu.DevicePrimesPow2LastOne.View,
						gpu.DevicePrimesPow2LastSeven.View,
						gpu.DevicePrimesPow2LastThree.View,
						gpu.DevicePrimesPow2LastNine.View,
						outputView);
		accelerator.Synchronize();
		outputView.CopyToCPU(ref flag, 1);

		gpu.Dispose();
		limiter.Dispose();

		return flag != 0;
	}

	public static int GpuBatchSize { get; set; } = 262_144;

	[MethodImpl(MethodImplOptions.AggressiveInlining)]
	public static void IsPrimeBatchGpu(ReadOnlySpan<ulong> values, Span<byte> results)
	{
		var limiter = GpuPrimeWorkLimiter.Acquire();
		var gpu = PrimeTesterGpuContextPool.Rent(GpuBatchSize);
		var accelerator = gpu.Accelerator;
		var kernel = gpu.Kernel;
		int totalLength = values.Length;
		int batchSize = GpuBatchSize;

		var input = gpu.Input;
		var output = gpu.Output;
		var inputView = input.View;
		var outputView = output.View;

		int pos = 0;
		while (pos < totalLength)
		{
			int remaining = totalLength - pos;
			int count = remaining > batchSize ? batchSize : remaining;

			var valueSlice = values.Slice(pos, count);
			ref ulong valueRef = ref MemoryMarshal.GetReference(valueSlice);
			inputView.CopyFromCPU(ref valueRef, count);

			kernel(
					count,
					inputView,
					gpu.DevicePrimesDefault.View,
					gpu.DevicePrimesLastOne.View,
					gpu.DevicePrimesLastSeven.View,
					gpu.DevicePrimesLastThree.View,
					gpu.DevicePrimesLastNine.View,
					gpu.DevicePrimesPow2Default.View,
					gpu.DevicePrimesPow2LastOne.View,
					gpu.DevicePrimesPow2LastSeven.View,
					gpu.DevicePrimesPow2LastThree.View,
					gpu.DevicePrimesPow2LastNine.View,
					outputView);
			accelerator.Synchronize();
			var resultSlice = results.Slice(pos, count);
			ref byte resultRef = ref MemoryMarshal.GetReference(resultSlice);
			outputView.CopyToCPU(ref resultRef, count);

			pos += count;
		}

		gpu.Dispose();
		limiter.Dispose();
	}

	internal static class PrimeTesterGpuContextPool
	{
		private static readonly ConcurrentQueue<PrimeTesterGpuContextLease> Pool = new();

		internal static PrimeTesterGpuContextLease Rent(int minBufferCapacity = 1)
		{
			if (!Pool.TryDequeue(out var lease))
			{
				lease = new PrimeTesterGpuContextLease(minBufferCapacity);
			}
			else
			{
				lease.EnsureCapacity(minBufferCapacity);
			}

			lease.ResetReturnFlag();
			return lease;
		}

		internal static void Return(PrimeTesterGpuContextLease lease)
		{
			lease.Accelerator.Synchronize();
			Pool.Enqueue(lease);
		}

		internal static void DisposeAll()
		{
			while (Pool.TryDequeue(out var lease))
			{
				lease.DisposeResources();
			}
		}

		internal static void Clear(Accelerator accelerator)
		{
			if (accelerator is null)
			{
				return;
			}

			var retained = new List<PrimeTesterGpuContextLease>();
			while (Pool.TryDequeue(out var lease))
			{
				if (lease.Accelerator == accelerator)
				{
					lease.DisposeResources();
				}
				else
				{
					retained.Add(lease);
				}
			}

			int retainedCount = retained.Count;
			for (int i = 0; i < retainedCount; i++)
			{
				Pool.Enqueue(retained[i]);
			}
		}

		internal sealed class PrimeTesterGpuContextLease : IDisposable
		{
			private bool _returned;

			internal readonly Context AcceleratorContext;
			public readonly Accelerator Accelerator;
			public readonly Action<Index1D, ArrayView<ulong>, ArrayView<uint>, ArrayView<uint>, ArrayView<uint>, ArrayView<uint>, ArrayView<uint>, ArrayView<ulong>, ArrayView<ulong>, ArrayView<ulong>, ArrayView<ulong>, ArrayView<ulong>, ArrayView<byte>> Kernel;
			public readonly Action<Index1D, ArrayView<ulong>, ulong, ArrayView<int>> HeuristicTrialDivisionKernel;
			public readonly MemoryBuffer1D<uint, Stride1D.Dense> DevicePrimesDefault;
			public readonly MemoryBuffer1D<uint, Stride1D.Dense> DevicePrimesLastOne;
			public readonly MemoryBuffer1D<uint, Stride1D.Dense> DevicePrimesLastSeven;
			public readonly MemoryBuffer1D<uint, Stride1D.Dense> DevicePrimesLastThree;
			public readonly MemoryBuffer1D<uint, Stride1D.Dense> DevicePrimesLastNine;
			public readonly MemoryBuffer1D<ulong, Stride1D.Dense> DevicePrimesPow2Default;
			public readonly MemoryBuffer1D<ulong, Stride1D.Dense> DevicePrimesPow2LastOne;
			public readonly MemoryBuffer1D<ulong, Stride1D.Dense> DevicePrimesPow2LastSeven;
			public readonly MemoryBuffer1D<ulong, Stride1D.Dense> DevicePrimesPow2LastThree;
			public readonly MemoryBuffer1D<ulong, Stride1D.Dense> DevicePrimesPow2LastNine;
			public MemoryBuffer1D<ulong, Stride1D.Dense> Input;
			public MemoryBuffer1D<byte, Stride1D.Dense> Output;
			public MemoryBuffer1D<int, Stride1D.Dense> HeuristicFlag;
			public int BufferCapacity;
	        public ulong[] DivisorArray;

			internal PrimeTesterGpuContextLease(int minBufferCapacity)
			{
				AcceleratorContext = Context.CreateDefault();
				Accelerator = AcceleratorContext.GetPreferredDevice(false).CreateAccelerator(AcceleratorContext);
				Kernel = Accelerator.LoadAutoGroupedStreamKernel<Index1D, ArrayView<ulong>, ArrayView<uint>, ArrayView<uint>, ArrayView<uint>, ArrayView<uint>, ArrayView<uint>, ArrayView<ulong>, ArrayView<ulong>, ArrayView<ulong>, ArrayView<ulong>, ArrayView<ulong>, ArrayView<byte>>(PrimeTesterKernels.SmallPrimeSieveKernel);
				HeuristicTrialDivisionKernel = Accelerator.LoadAutoGroupedStreamKernel<Index1D, ArrayView<ulong>, ulong, ArrayView<int>>(PrimeTesterKernels.HeuristicTrialDivisionKernel);

				var primesDefault = DivisorGenerator.SmallPrimes;
				DevicePrimesDefault = Accelerator.Allocate1D<uint>(primesDefault.Length);
				DevicePrimesDefault.View.CopyFromCPU(primesDefault);

				var primesLastOne = DivisorGenerator.SmallPrimesLastOne;
				DevicePrimesLastOne = Accelerator.Allocate1D<uint>(primesLastOne.Length);
				DevicePrimesLastOne.View.CopyFromCPU(primesLastOne);

				var primesLastSeven = DivisorGenerator.SmallPrimesLastSeven;
				DevicePrimesLastSeven = Accelerator.Allocate1D<uint>(primesLastSeven.Length);
				DevicePrimesLastSeven.View.CopyFromCPU(primesLastSeven);

				var primesLastThree = DivisorGenerator.SmallPrimesLastThree;
				DevicePrimesLastThree = Accelerator.Allocate1D<uint>(primesLastThree.Length);
				DevicePrimesLastThree.View.CopyFromCPU(primesLastThree);

				var primesLastNine = DivisorGenerator.SmallPrimesLastNine;
				DevicePrimesLastNine = Accelerator.Allocate1D<uint>(primesLastNine.Length);
				DevicePrimesLastNine.View.CopyFromCPU(primesLastNine);

				var primesPow2Default = DivisorGenerator.SmallPrimesPow2;
				DevicePrimesPow2Default = Accelerator.Allocate1D<ulong>(primesPow2Default.Length);
				DevicePrimesPow2Default.View.CopyFromCPU(primesPow2Default);

				var primesPow2LastOne = DivisorGenerator.SmallPrimesPow2LastOne;
				DevicePrimesPow2LastOne = Accelerator.Allocate1D<ulong>(primesPow2LastOne.Length);
				DevicePrimesPow2LastOne.View.CopyFromCPU(primesPow2LastOne);

				var primesPow2LastSeven = DivisorGenerator.SmallPrimesPow2LastSeven;
				DevicePrimesPow2LastSeven = Accelerator.Allocate1D<ulong>(primesPow2LastSeven.Length);
				DevicePrimesPow2LastSeven.View.CopyFromCPU(primesPow2LastSeven);

				var primesPow2LastThree = DivisorGenerator.SmallPrimesPow2LastThree;
				DevicePrimesPow2LastThree = Accelerator.Allocate1D<ulong>(primesPow2LastThree.Length);
				DevicePrimesPow2LastThree.View.CopyFromCPU(primesPow2LastThree);

				var primesPow2LastNine = DivisorGenerator.SmallPrimesPow2LastNine;
				DevicePrimesPow2LastNine = Accelerator.Allocate1D<ulong>(primesPow2LastNine.Length);
				DevicePrimesPow2LastNine.View.CopyFromCPU(primesPow2LastNine);

				BufferCapacity = minBufferCapacity;
				Input = Accelerator.Allocate1D<ulong>(minBufferCapacity);
				Output = Accelerator.Allocate1D<byte>(minBufferCapacity);
				HeuristicFlag = Accelerator.Allocate1D<int>(minBufferCapacity);
				DivisorArray = ThreadStaticPools.UlongPool.Rent(minBufferCapacity);

				_returned = false;
			}

			public void EnsureCapacity(int minCapacity)
			{
				int required = minCapacity;
				if (required <= BufferCapacity)
				{
					return;
				}

				Input.Dispose();
				Output.Dispose();
				HeuristicFlag.Dispose();
				ThreadStaticPools.UlongPool.Return(DivisorArray);
				Input = Accelerator.Allocate1D<ulong>(required);
				Output = Accelerator.Allocate1D<byte>(required);
				HeuristicFlag = Accelerator.Allocate1D<int>(required);
				DivisorArray = ThreadStaticPools.UlongPool.Rent(required);
				BufferCapacity = required;
			}

			internal void ResetReturnFlag()
			{
				_returned = false;
			}

			public void Dispose()
			{
				if (_returned)
				{
					return;
				}

				_returned = true;
				PrimeTesterGpuContextPool.Return(this);
			}

			internal void DisposeResources()
			{
				Input.Dispose();
				Output.Dispose();
				HeuristicFlag.Dispose();
				DevicePrimesDefault.Dispose();
				DevicePrimesLastOne.Dispose();
				DevicePrimesLastSeven.Dispose();
				DevicePrimesLastThree.Dispose();
				DevicePrimesLastNine.Dispose();
				DevicePrimesPow2Default.Dispose();
				DevicePrimesPow2LastOne.Dispose();
				DevicePrimesPow2LastSeven.Dispose();
				DevicePrimesPow2LastThree.Dispose();
				DevicePrimesPow2LastNine.Dispose();
				Accelerator.Dispose();
				AcceleratorContext.Dispose();
			}
		}
	}
	// Expose cache clearing for accelerator disposal coordination
	public static void ClearGpuCaches(Accelerator accelerator)
	{
		PrimeTesterGpuContextPool.Clear(accelerator);
	}

	internal static void DisposeGpuContexts()
	{
		PrimeTesterGpuContextPool.DisposeAll();
	}

	[MethodImpl(MethodImplOptions.AggressiveInlining)]
	internal static bool SharesFactorWithMaxExponent(ulong n)
	{
		// TODO: Replace this on-the-fly GCD probe with the cached factor table derived from
		// ResidueComputationBenchmarks so divisor-cycle metadata can short-circuit the test
		// instead of recomputing binary GCD for every candidate.
		ulong m = (ulong)BitOperations.Log2(n);
		return BinaryGcd(n, m) != 1UL;
	}

	internal static void SharesFactorWithMaxExponentBatch(ReadOnlySpan<ulong> values, Span<byte> results)
	{
		// TODO: Route this batch helper through the shared GPU kernel pool from
		// GpuUInt128BinaryGcdBenchmarks so we reuse cached kernels, pinned host buffers,
		// and divisor-cycle staging instead of allocating new device buffers per call.
		var gpu = PrimeTesterGpuContextPool.Rent();
		var accelerator = gpu.Accelerator;
		var kernel = accelerator.LoadAutoGroupedStreamKernel<Index1D, ArrayView<ulong>, ArrayView<byte>>(PrimeTesterKernels.SharesFactorKernel);

		int length = values.Length;
		var inputBuffer = accelerator.Allocate1D<ulong>(length);
		var resultBuffer = accelerator.Allocate1D<byte>(length);

		ArrayPool<ulong> pool = ThreadStaticPools.UlongPool;
		ulong[] temp = pool.Rent(length);
		values.CopyTo(temp);
		inputBuffer.View.CopyFromCPU(ref temp[0], length);
		kernel(length, inputBuffer.View, resultBuffer.View);
		accelerator.Synchronize();
		resultBuffer.View.CopyToCPU(ref results[0], length);
		pool.Return(temp, clearArray: false);
		resultBuffer.Dispose();
		inputBuffer.Dispose();
		gpu.Dispose();
	}

	[MethodImpl(MethodImplOptions.AggressiveInlining)]
	private static ulong BinaryGcd(ulong u, ulong v)
	{
		// TODO: Swap this handwritten binary GCD for the optimized helper measured in
		// GpuUInt128BinaryGcdBenchmarks so CPU callers share the faster subtract-less
		// ladder once the common implementation is promoted into PerfectNumbers.Core.
		if (u == 0UL)
		{
			return v;
		}

		if (v == 0UL)
		{
			return u;
		}

		int shift = BitOperations.TrailingZeroCount(u | v);
		u >>= BitOperations.TrailingZeroCount(u);

		do
		{
			v >>= BitOperations.TrailingZeroCount(v);
			if (u > v)
			{
				(u, v) = (v, u);
			}

			v -= u;
		}
		while (v != 0UL);

		return u << shift;
	}
}