938 lines
33 KiB
C#
938 lines
33 KiB
C#
using System.Buffers;
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using System.Collections.Concurrent;
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using System.Runtime.CompilerServices;
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using ILGPU;
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using ILGPU.Runtime;
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using UInt128 = System.UInt128;
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namespace PerfectNumbers.Core.Gpu;
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public class MersenneNumberLucasLehmerGpuTester
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{
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private readonly ConcurrentDictionary<Accelerator, Action<Index1D, ulong, GpuUInt128, ArrayView<GpuUInt128>>> KernelCache = new();
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private readonly ConcurrentDictionary<Accelerator, Action<Index1D, ulong, ArrayView<GpuUInt128>>> AddSmallKernelCache = new();
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private readonly ConcurrentDictionary<Accelerator, Action<Index1D, ulong, ArrayView<GpuUInt128>>> SubSmallKernelCache = new();
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private readonly ConcurrentDictionary<Accelerator, Action<Index1D, ulong, ArrayView<GpuUInt128>>> ReduceKernelCache = new();
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private readonly ConcurrentDictionary<Accelerator, Action<Index1D, ArrayView<GpuUInt128>, ArrayView<byte>>> IsZeroKernelCache = new();
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private readonly ConcurrentDictionary<Accelerator, Action<Index1D, ArrayView<ulong>, ArrayView<GpuUInt128>, ArrayView<GpuUInt128>>> BatchKernelCache = new();
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private Action<Index1D, ulong, GpuUInt128, ArrayView<GpuUInt128>> GetKernel(Accelerator accelerator)
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{
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return KernelCache.GetOrAdd(accelerator, accel => accel.LoadAutoGroupedStreamKernel<Index1D, ulong, GpuUInt128, ArrayView<GpuUInt128>>(Kernel));
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}
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private Action<Index1D, ulong, ArrayView<GpuUInt128>> GetAddSmallKernel(Accelerator accelerator) =>
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AddSmallKernelCache.GetOrAdd(accelerator, acc => acc.LoadAutoGroupedStreamKernel<Index1D, ulong, ArrayView<GpuUInt128>>(AddSmallKernel));
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private Action<Index1D, ulong, ArrayView<GpuUInt128>> GetSubSmallKernel(Accelerator accelerator) =>
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SubSmallKernelCache.GetOrAdd(accelerator, acc => acc.LoadAutoGroupedStreamKernel<Index1D, ulong, ArrayView<GpuUInt128>>(SubtractSmallKernel));
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private Action<Index1D, ulong, ArrayView<GpuUInt128>> GetReduceKernel(Accelerator accelerator) =>
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ReduceKernelCache.GetOrAdd(accelerator, acc => acc.LoadAutoGroupedStreamKernel<Index1D, ulong, ArrayView<GpuUInt128>>(ReduceModMersenneKernel));
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private Action<Index1D, ArrayView<GpuUInt128>, ArrayView<byte>> GetIsZeroKernel(Accelerator accelerator) =>
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IsZeroKernelCache.GetOrAdd(accelerator, acc => acc.LoadAutoGroupedStreamKernel<Index1D, ArrayView<GpuUInt128>, ArrayView<byte>>(IsZeroKernel));
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private Action<Index1D, ArrayView<ulong>, ArrayView<GpuUInt128>, ArrayView<GpuUInt128>> GetBatchKernel(Accelerator accelerator) =>
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BatchKernelCache.GetOrAdd(accelerator, acc => acc.LoadAutoGroupedStreamKernel<Index1D, ArrayView<ulong>, ArrayView<GpuUInt128>, ArrayView<GpuUInt128>>(KernelBatch));
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// Configurable LL slice size to keep kernels short. Default 32.
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public int SliceSize = 32;
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public bool IsMersennePrime(ulong exponent)
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{
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// Default to global kernel preference for backward compatibility.
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bool runOnGpu = !GpuContextPool.ForceCpu;
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// TODO: Inline this wrapper once callers request IsPrime directly so the Lucas–Lehmer fast path
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// avoids an extra method frame; the LucasLehmerGpuBenchmarks showed the delegate hop shaving
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// measurable time off tight reload loops when removed.
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return IsPrime(exponent, runOnGpu);
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}
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public bool IsPrime(ulong exponent, bool runOnGpu)
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{
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// Early rejections aligned with incremental/order sieves, but safe for small p:
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// - If 3 | p and p != 3, then 7 | M_p -> composite.
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// - If p ≡ 1 (mod 4) and p shares a factor with (p-1), reject fast.
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// TODO: Replace this `% 3` guard with ULongExtensions.Mod3 once GPU LL filtering reuses the benchmarked bitmask helper.
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if ((exponent % 3UL) == 0UL && exponent != 3UL)
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{
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return false;
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}
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if ((exponent & 3UL) == 1UL && exponent.SharesFactorWithExponentMinusOne())
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{
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return false;
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}
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var limiter = GpuPrimeWorkLimiter.Acquire();
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bool result;
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if (exponent >= 128UL)
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{
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if (!TryGetNttParameters(exponent, out var nttMod, out var primitiveRoot))
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{
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limiter.Dispose();
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throw new NotSupportedException("NTT parameters for the given exponent are not available.");
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}
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result = IsMersennePrimeNtt(exponent, nttMod, primitiveRoot, runOnGpu);
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}
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else
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{
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var gpu = GpuContextPool.RentPreferred(preferCpu: !runOnGpu);
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var accelerator = gpu.Accelerator;
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var kernel = GetKernel(accelerator);
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var modulus = new GpuUInt128(((UInt128)1 << (int)exponent) - 1UL); // TODO: Cache these Mersenne moduli per exponent so LL GPU runs skip rebuilding them every launch.
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var buffer = accelerator.Allocate1D<GpuUInt128>(1);
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kernel(1, exponent, modulus, buffer.View);
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accelerator.Synchronize();
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result = buffer.GetAsArray1D()[0].IsZero;
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buffer.Dispose();
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gpu.Dispose();
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}
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limiter.Dispose();
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return result;
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}
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public void ComputeResidues(ReadOnlySpan<ulong> exponents, Span<GpuUInt128> residues)
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{
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int count = exponents.Length;
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if (residues.Length < count)
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{
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throw new ArgumentException("Result span too small", nameof(residues));
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}
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for (int i = 0; i < count; i++)
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{
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if (exponents[i] >= 128UL)
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{
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throw new NotSupportedException("Batch residue calculation supports exponents < 128 only.");
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}
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}
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var gpu = GpuContextPool.RentPreferred(preferCpu: false);
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var accelerator = gpu.Accelerator;
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var kernel = GetBatchKernel(accelerator); // TODO: Switch this batch path to the ProcessEightBitWindows residue kernel once Lucas–Lehmer integrates the benchmarked windowed pow2 helper for small exponents.
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var expBuffer = accelerator.Allocate1D<ulong>(count);
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ulong[] expArray = ArrayPool<ulong>.Shared.Rent(count);
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exponents.CopyTo(expArray);
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expBuffer.View.CopyFromCPU(ref expArray[0], count);
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GpuUInt128[] modulusArray = ArrayPool<GpuUInt128>.Shared.Rent(count);
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for (int i = 0; i < count; i++)
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{
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// TODO: Replace this per-exponent shift with a small shared table (one entry per supported exponent < 128)
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// so Lucas–Lehmer batch runs reuse cached GpuUInt128 moduli instead of rebuilding them for every request.
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modulusArray[i] = new GpuUInt128(((UInt128)1 << (int)exponents[i]) - 1UL);
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}
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var modBuffer = accelerator.Allocate1D<GpuUInt128>(count);
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modBuffer.View.CopyFromCPU(ref modulusArray[0], count);
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var stateBuffer = accelerator.Allocate1D<GpuUInt128>(count);
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kernel(count, expBuffer.View, modBuffer.View, stateBuffer.View);
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accelerator.Synchronize();
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stateBuffer.View.CopyToCPU(ref residues[0], count);
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stateBuffer.Dispose();
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modBuffer.Dispose();
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expBuffer.Dispose();
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ArrayPool<GpuUInt128>.Shared.Return(modulusArray);
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ArrayPool<ulong>.Shared.Return(expArray);
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gpu.Dispose();
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}
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public void IsMersennePrimeBatch(ReadOnlySpan<ulong> exponents, Span<bool> results)
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{
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int count = exponents.Length;
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if (results.Length < count)
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{
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throw new ArgumentException("Result span too small", nameof(results));
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}
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GpuUInt128[] buffer = ArrayPool<GpuUInt128>.Shared.Rent(count);
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try
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{
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ComputeResidues(exponents, buffer.AsSpan(0, count));
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for (int i = 0; i < count; i++)
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{
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results[i] = buffer[i].IsZero;
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}
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}
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finally
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{
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ArrayPool<GpuUInt128>.Shared.Return(buffer);
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}
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}
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private bool IsMersennePrimeNtt(ulong exponent, GpuUInt128 nttMod, GpuUInt128 primitiveRoot, bool runOnGpu)
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{
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var gpu = GpuContextPool.RentPreferred(preferCpu: !runOnGpu);
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var accelerator = gpu.Accelerator;
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var addKernel = GetAddSmallKernel(accelerator);
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var subKernel = GetSubSmallKernel(accelerator);
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var reduceKernel = GetReduceKernel(accelerator);
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var zeroKernel = GetIsZeroKernel(accelerator);
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int limbCount = (int)((exponent + 127UL) / 128UL);
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int target = limbCount * 2;
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int transformLength = 1;
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while (transformLength < target)
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{
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transformLength <<= 1;
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}
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var stateBuffer = accelerator.Allocate1D<GpuUInt128>(transformLength);
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stateBuffer.MemSetToZero();
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addKernel(1, 4UL, stateBuffer.View);
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// TODO(LL-SLICE): Slice Lucas–Lehmer iterations into short batches to
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// avoid long-running kernels and TDR. Example: process 8–64 iterations
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// per slice, with synchronization between slices. Combine this with
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// stage-wise NTT to ensure each kernel stays < ~0.5–1.0s.
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ulong i = 0UL;
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ulong limit = exponent - 2UL;
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int slice = Math.Max(1, SliceSize); // process LL iterations in small slices
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while (i < limit)
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{
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int iter = (int)Math.Min((ulong)slice, limit - i);
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for (int s = 0; s < iter; s++)
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{
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// Square in NTT domain with staged kernels (short runtime per kernel).
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NttGpuMath.SquareDevice(accelerator, stateBuffer.View, nttMod, primitiveRoot);
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subKernel(1, 2UL, stateBuffer.View);
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reduceKernel(1, exponent, stateBuffer.View);
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}
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// Synchronize between slices to yield to scheduler and avoid TDR.
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accelerator.Synchronize();
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i += (ulong)iter;
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}
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reduceKernel(1, exponent, stateBuffer.View);
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var resultBuffer = accelerator.Allocate1D<byte>(1);
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zeroKernel(1, stateBuffer.View, resultBuffer.View);
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accelerator.Synchronize();
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byte[] result = new byte[1];
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resultBuffer.View.CopyToCPU(result);
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bool isPrime = result[0] != 0;
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resultBuffer.Dispose();
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stateBuffer.Dispose();
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gpu.Dispose();
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return isPrime;
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}
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private static readonly ConcurrentDictionary<int, (GpuUInt128 Modulus, GpuUInt128 PrimitiveRoot)> NttParameterCache = new()
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{
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// 2^12 transform length using a 64-bit NTT-friendly prime
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[4096] = (new GpuUInt128(0UL, 18446744069414584321UL), new GpuUInt128(0UL, 7UL)),
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// 2^22 transform length precomputed for p ~= 138,000,000
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[4194304] = (new GpuUInt128(0UL, 104857601UL), new GpuUInt128(0UL, 39193363UL))
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};
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private readonly object ParameterFileLock = new();
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private readonly string ParameterFilePath = Path.Combine(AppContext.BaseDirectory, "ntt-params.txt");
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public void WarmUpNttParameters(ulong exponent)
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{
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_ = TryGetNttParameters(exponent, out _, out _);
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}
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private bool TryGetNttParameters(ulong exponent, out GpuUInt128 modulus, out GpuUInt128 primitiveRoot)
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{
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int limbCount = (int)((exponent + 127UL) / 128UL);
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int length = 1;
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int target = limbCount * 2;
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while (length < target)
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{
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length <<= 1;
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}
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if (NttParameterCache.TryGetValue(length, out var cached))
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{
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modulus = cached.Modulus;
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primitiveRoot = cached.PrimitiveRoot;
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return true;
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}
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if (TryLoadPersistedParameters(length, out modulus, out primitiveRoot))
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{
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NttParameterCache[length] = (modulus, primitiveRoot);
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return true;
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}
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if (GenerateNttParameters(length, out modulus, out primitiveRoot))
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{
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NttParameterCache[length] = (modulus, primitiveRoot);
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PersistParameters(length, modulus, primitiveRoot);
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return true;
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}
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modulus = new GpuUInt128(0UL, 18446744069414584321UL); // 2^64 - 2^32 + 1
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primitiveRoot = new GpuUInt128(0UL, 7UL);
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return false;
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}
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private bool TryLoadPersistedParameters(int length, out GpuUInt128 modulus, out GpuUInt128 primitiveRoot)
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{
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if (!File.Exists(ParameterFilePath))
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{
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modulus = new GpuUInt128(0UL, 0UL);
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primitiveRoot = new GpuUInt128(0UL, 0UL);
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return false;
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}
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foreach (var line in File.ReadLines(ParameterFilePath))
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{
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if (string.IsNullOrWhiteSpace(line))
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{
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continue;
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}
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var parts = line.Split(' ', StringSplitOptions.RemoveEmptyEntries);
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if (parts.Length != 5)
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{
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continue;
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}
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// TODO: Replace int.TryParse with the span-based Utf8Parser helper when loading cached parameters so we avoid
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// culture-aware parsing in this hot startup loop.
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if (!int.TryParse(parts[0], out var storedLength) || storedLength != length)
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{
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continue;
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}
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// TODO: Switch these ulong.Parse calls to the Utf8Parser-based fast-path once we expose a zero-allocation reader for
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// persisted kernel parameters.
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ulong modHigh = ulong.Parse(parts[1]);
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ulong modLow = ulong.Parse(parts[2]);
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ulong rootHigh = ulong.Parse(parts[3]);
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ulong rootLow = ulong.Parse(parts[4]);
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modulus = new GpuUInt128(modHigh, modLow);
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primitiveRoot = new GpuUInt128(rootHigh, rootLow);
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return true;
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}
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modulus = new GpuUInt128(0UL, 0UL);
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primitiveRoot = new GpuUInt128(0UL, 0UL);
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return false;
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}
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private void PersistParameters(int length, GpuUInt128 modulus, GpuUInt128 primitiveRoot)
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{
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lock (ParameterFileLock)
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{
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// TODO: Replace StreamWriter with the pooled TextFileWriter pipeline so persisting NTT
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// parameters reuses the zero-allocation buffered writes highlighted in the scanner I/O
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// benchmarks instead of allocating a new encoder per append.
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using var writer = new StreamWriter(ParameterFilePath, append: true);
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writer.WriteLine($"{length} {modulus.High} {modulus.Low} {primitiveRoot.High} {primitiveRoot.Low}");
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}
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}
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private static bool GenerateNttParameters(int length, out GpuUInt128 modulus, out GpuUInt128 primitiveRoot)
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{
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ulong foundCandidate = 0UL;
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ulong foundRoot = 0UL;
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bool success = false;
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var processorCount = Environment.ProcessorCount;
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using var cts = new System.Threading.CancellationTokenSource();
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object sync = new();
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// TODO: Move this Parallel.For to the shared low-overhead work scheduler once the NTT parameter
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// generator integrates with the GPU-first pipeline so parameter scans reuse the same batching
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// strategy measured fastest in the divisor-cycle benchmarks.
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System.Threading.Tasks.Parallel.For(0, processorCount, (worker, state) =>
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{
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ulong k = (ulong)worker + 1UL;
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while (!cts.IsCancellationRequested)
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{
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ulong candidate;
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try
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{
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candidate = checked((ulong)length * k + 1UL);
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}
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catch (OverflowException)
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{
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break;
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}
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if (IsPrime(candidate))
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{
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ulong root = FindPrimitiveRoot(candidate, (ulong)length);
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lock (sync)
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{
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foundCandidate = candidate;
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foundRoot = root;
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success = true;
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cts.Cancel();
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state.Stop();
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}
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break;
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}
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k += (ulong)processorCount;
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}
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});
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if (success)
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{
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modulus = new GpuUInt128(0UL, foundCandidate);
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primitiveRoot = new GpuUInt128(0UL, foundRoot);
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return true;
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}
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modulus = new GpuUInt128(0UL, 18446744069414584321UL);
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primitiveRoot = new GpuUInt128(0UL, 7UL);
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return false;
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}
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private static ulong FindPrimitiveRoot(ulong modulus, ulong order)
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{
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ulong phi = modulus - 1UL;
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// TODO: Reuse the divisor-cycle cache to factor phi via the precomputed small-prime windows once
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// the lookup tables land so primitive root searches stop iterating over slow trial divisions.
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var factors = Factorize(phi);
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for (ulong g = 2UL; g < modulus; g++)
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{
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bool ok = true;
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foreach (ulong f in factors)
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{
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if (ModPow(g, phi / f, modulus) == 1UL)
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{
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ok = false;
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break;
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}
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}
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if (ok)
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{
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return ModPow(g, phi / order, modulus);
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}
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}
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throw new InvalidOperationException("Primitive root not found.");
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}
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private static List<ulong> Factorize(ulong n)
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{
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var factors = new List<ulong>();
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for (ulong p = 2UL; p * p <= n; p += p == 2UL ? 1UL : 2UL)
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{
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// TODO: Replace these `%` factor checks with the shared Mod helpers (Mod3/Mod5/etc.) once the GPU
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// pre-filter adopts the benchmarked bitmask operations to avoid slow modulo instructions.
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if (n % p == 0UL)
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{
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factors.Add(p);
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while (n % p == 0UL)
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{
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n /= p;
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}
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}
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}
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if (n > 1UL)
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{
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factors.Add(n);
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}
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return factors;
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}
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private static bool IsPrime(ulong n)
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{
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if (n < 2UL)
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{
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return false;
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}
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if ((n & 1UL) == 0UL)
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{
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return n == 2UL;
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}
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for (ulong divisor = 3UL; divisor * divisor <= n; divisor += 2UL)
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{
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// TODO: Swap this `%` for the divisor-cycle aware Mod helper once the residue pre-checks expose it
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// so primality filtering avoids slow modulo instructions in tight loops.
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if (n % divisor == 0UL)
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{
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return false;
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}
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}
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return true;
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}
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private static ulong ModPow(ulong value, ulong exponent, ulong modulus)
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{
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ulong result = 1UL;
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while (exponent > 0UL)
|
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{
|
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if ((exponent & 1UL) != 0UL)
|
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{
|
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// TODO: Route these powmods through the ProcessEightBitWindows helper once it lands for GPU
|
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// host-side fallbacks so the Lucas–Lehmer setup reuses the benchmarked windowed ladder.
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result = MulMod(result, value, modulus);
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}
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value = MulMod(value, value, modulus);
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exponent >>= 1;
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}
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return result;
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}
|
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|
||
private static ulong MulMod(ulong a, ulong b, ulong modulus)
|
||
{
|
||
// TODO: Swap this UInt128 `%` reduction for the GPU-compatible MulMod helper once it adopts the faster
|
||
// inline UInt128 path benchmarked in MulMod64Benchmarks so host/GPU parity avoids BigInteger-style fallbacks.
|
||
return (ulong)(((UInt128)a * b) % modulus);
|
||
}
|
||
|
||
private static void AddSmallKernel(Index1D index, ulong add, ArrayView<GpuUInt128> value)
|
||
{
|
||
ulong carry = add;
|
||
for (int i = 0; i < value.Length && carry != 0UL; i++)
|
||
{
|
||
var limb = value[i];
|
||
ulong low = limb.Low + carry;
|
||
ulong carryOut = low < carry ? 1UL : 0UL;
|
||
ulong high = limb.High + carryOut;
|
||
carry = high < limb.High ? 1UL : 0UL;
|
||
value[i] = new GpuUInt128(high, low);
|
||
}
|
||
}
|
||
|
||
private static void SubtractSmallKernel(Index1D index, ulong subtract, ArrayView<GpuUInt128> value)
|
||
{
|
||
ulong borrow = subtract;
|
||
for (int i = 0; i < value.Length && borrow != 0UL; i++)
|
||
{
|
||
var limb = value[i];
|
||
ulong low = limb.Low;
|
||
ulong high = limb.High;
|
||
if (low >= borrow)
|
||
{
|
||
low -= borrow;
|
||
borrow = 0UL;
|
||
}
|
||
else
|
||
{
|
||
low = unchecked(low - borrow);
|
||
borrow = 1UL;
|
||
if (high != 0UL)
|
||
{
|
||
high--;
|
||
borrow = 0UL;
|
||
}
|
||
else
|
||
{
|
||
high = ulong.MaxValue;
|
||
}
|
||
}
|
||
|
||
value[i] = new GpuUInt128(high, low);
|
||
}
|
||
}
|
||
|
||
private static void ReduceModMersenneKernel(Index1D index, ulong exponent, ArrayView<GpuUInt128> value)
|
||
{
|
||
int limbCount = (int)((exponent + 127UL) / 128UL);
|
||
for (int i = limbCount; i < value.Length; i++)
|
||
{
|
||
var limb = value[i];
|
||
if (limb.IsZero)
|
||
{
|
||
continue;
|
||
}
|
||
|
||
int target = i - limbCount;
|
||
var sum = value[target];
|
||
var original = sum;
|
||
sum.Add(limb);
|
||
value[target] = sum;
|
||
value[i] = new GpuUInt128(0UL, 0UL);
|
||
if (sum.CompareTo(original) < 0)
|
||
{
|
||
int j = target + 1;
|
||
while (j < limbCount)
|
||
{
|
||
var next = value[j];
|
||
var nextOriginal = next;
|
||
next.Add(1UL);
|
||
value[j] = next;
|
||
if (next.CompareTo(nextOriginal) >= 0)
|
||
{
|
||
break;
|
||
}
|
||
|
||
j++;
|
||
}
|
||
}
|
||
}
|
||
|
||
int topBits = (int)exponent.Mod128();
|
||
if (topBits == 0)
|
||
{
|
||
topBits = 128;
|
||
}
|
||
|
||
int topIndex = limbCount - 1;
|
||
ulong topLowMask = topBits >= 64 ? ulong.MaxValue : (1UL << topBits) - 1UL;
|
||
ulong topHighMask = topBits > 64 ? (1UL << (topBits - 64)) - 1UL : 0UL;
|
||
var top = value[topIndex];
|
||
var carryBits = top >> topBits;
|
||
top = new(top.High & topHighMask, top.Low & topLowMask);
|
||
value[topIndex] = top;
|
||
|
||
if (!carryBits.IsZero)
|
||
{
|
||
int j = 0;
|
||
while (j < limbCount && !carryBits.IsZero)
|
||
{
|
||
var cur = value[j];
|
||
var curOriginal = cur;
|
||
cur.Add(carryBits);
|
||
value[j] = cur;
|
||
carryBits = cur.CompareTo(curOriginal) < 0 ? new GpuUInt128(0UL, 1UL) : new GpuUInt128(0UL, 0UL);
|
||
j++;
|
||
}
|
||
}
|
||
|
||
bool geq = true;
|
||
for (int i = topIndex; i >= 0; i--)
|
||
{
|
||
var limb = value[i];
|
||
ulong modHigh = i == topIndex ? topHighMask : ulong.MaxValue;
|
||
ulong modLow = i == topIndex ? topLowMask : ulong.MaxValue;
|
||
if (limb.High > modHigh || (limb.High == modHigh && limb.Low > modLow))
|
||
{
|
||
geq = true;
|
||
break;
|
||
}
|
||
|
||
if (limb.High < modHigh || (limb.High == modHigh && limb.Low < modLow))
|
||
{
|
||
geq = false;
|
||
break;
|
||
}
|
||
}
|
||
|
||
if (geq)
|
||
{
|
||
ulong borrow = 0UL;
|
||
for (int i = 0; i < limbCount - 1; i++)
|
||
{
|
||
var limb = value[i];
|
||
ulong newLow = limb.Low - ulong.MaxValue - borrow;
|
||
borrow = limb.Low < ulong.MaxValue + borrow ? 1UL : 0UL;
|
||
ulong newHigh = limb.High - ulong.MaxValue - borrow;
|
||
borrow = limb.High < ulong.MaxValue + borrow ? 1UL : 0UL;
|
||
value[i] = new GpuUInt128(newHigh, newLow);
|
||
}
|
||
|
||
var topLimb = value[topIndex];
|
||
ulong newTopLow = topLimb.Low - topLowMask - borrow;
|
||
borrow = topLimb.Low < topLowMask + borrow ? 1UL : 0UL;
|
||
ulong newTopHigh = topLimb.High - topHighMask - borrow;
|
||
value[topIndex] = new GpuUInt128(newTopHigh, newTopLow);
|
||
}
|
||
|
||
for (int i = limbCount; i < value.Length; i++)
|
||
{
|
||
value[i] = new GpuUInt128(0UL, 0UL);
|
||
}
|
||
}
|
||
|
||
private static void IsZeroKernel(Index1D index, ArrayView<GpuUInt128> value, ArrayView<byte> result)
|
||
{
|
||
byte isZero = 1;
|
||
for (int i = 0; i < value.Length; i++)
|
||
{
|
||
var limb = value[i];
|
||
if (limb.High != 0UL || limb.Low != 0UL)
|
||
{
|
||
isZero = 0;
|
||
break;
|
||
}
|
||
}
|
||
|
||
result[0] = isZero;
|
||
}
|
||
|
||
private static void ReduceModMersenne(Span<GpuUInt128> value, ulong exponent)
|
||
{
|
||
int limbCount = (int)((exponent + 127UL) / 128UL);
|
||
for (int i = limbCount; i < value.Length; i++)
|
||
{
|
||
var limb = value[i];
|
||
if (limb.IsZero)
|
||
{
|
||
continue;
|
||
}
|
||
|
||
int target = i - limbCount;
|
||
UInt128 original = value[target];
|
||
UInt128 sum = original + (UInt128)limb;
|
||
bool carry = sum < original;
|
||
value[target] = new GpuUInt128(sum);
|
||
value[i] = new GpuUInt128(0UL, 0UL);
|
||
if (carry)
|
||
{
|
||
int j = target + 1;
|
||
while (j < limbCount)
|
||
{
|
||
UInt128 next = value[j];
|
||
UInt128 nextSum = next + 1UL;
|
||
value[j] = new GpuUInt128(nextSum);
|
||
if (nextSum != 0UL)
|
||
{
|
||
break;
|
||
}
|
||
|
||
j++;
|
||
}
|
||
}
|
||
}
|
||
|
||
int topBits = (int)exponent.Mod128();
|
||
if (topBits == 0)
|
||
{
|
||
topBits = 128;
|
||
}
|
||
|
||
int topIndex = limbCount - 1;
|
||
ulong topLowMask = topBits >= 64 ? ulong.MaxValue : (1UL << topBits) - 1UL;
|
||
ulong topHighMask = topBits > 64 ? (1UL << (topBits - 64)) - 1UL : 0UL;
|
||
UInt128 mask = ((UInt128)topHighMask << 64) | topLowMask;
|
||
UInt128 top = value[topIndex];
|
||
UInt128 carryBits = top >> topBits;
|
||
top &= mask;
|
||
value[topIndex] = new GpuUInt128(top);
|
||
if (carryBits != 0UL)
|
||
{
|
||
int j = 0;
|
||
UInt128 carry = carryBits;
|
||
while (j < limbCount && carry != 0UL)
|
||
{
|
||
UInt128 cur = value[j];
|
||
UInt128 sum = cur + carry;
|
||
bool overflow = sum < cur;
|
||
value[j] = new GpuUInt128(sum);
|
||
carry = overflow ? 1UL : 0UL;
|
||
j++;
|
||
}
|
||
}
|
||
|
||
bool geq = true;
|
||
for (int i = topIndex; i >= 0; i--)
|
||
{
|
||
UInt128 limb = value[i];
|
||
UInt128 modLimb = i == topIndex ? mask : UInt128.MaxValue;
|
||
if (limb > modLimb)
|
||
{
|
||
geq = true;
|
||
break;
|
||
}
|
||
|
||
if (limb < modLimb)
|
||
{
|
||
geq = false;
|
||
break;
|
||
}
|
||
}
|
||
|
||
if (geq)
|
||
{
|
||
ulong borrow = 0UL;
|
||
for (int i = 0; i < limbCount - 1; i++)
|
||
{
|
||
ulong low = value[i].Low;
|
||
ulong high = value[i].High;
|
||
ulong newLow = low - ulong.MaxValue - borrow;
|
||
borrow = low < ulong.MaxValue + borrow ? 1UL : 0UL;
|
||
ulong newHigh = high - ulong.MaxValue - borrow;
|
||
borrow = high < ulong.MaxValue + borrow ? 1UL : 0UL;
|
||
value[i] = new GpuUInt128(newHigh, newLow);
|
||
}
|
||
|
||
ulong topLow = value[topIndex].Low;
|
||
ulong topHigh = value[topIndex].High;
|
||
ulong newTopLow = topLow - topLowMask - borrow;
|
||
borrow = topLow < topLowMask + borrow ? 1UL : 0UL;
|
||
ulong newTopHigh = topHigh - topHighMask - borrow;
|
||
value[topIndex] = new GpuUInt128(newTopHigh, newTopLow);
|
||
}
|
||
|
||
for (int i = limbCount; i < value.Length; i++)
|
||
{
|
||
value[i] = new GpuUInt128(0UL, 0UL);
|
||
}
|
||
}
|
||
|
||
private static void KernelBatch(Index1D index, ArrayView<ulong> exponents, ArrayView<GpuUInt128> moduli, ArrayView<GpuUInt128> states)
|
||
{
|
||
int idx = index.X;
|
||
ulong exponent = exponents[idx];
|
||
GpuUInt128 modulus = moduli[idx];
|
||
var s = new GpuUInt128(0UL, 4UL);
|
||
ulong limit = exponent - 2UL;
|
||
for (ulong i = 0UL; i < limit; i++)
|
||
{
|
||
s = SquareModMersenne128(s, exponent);
|
||
s.SubMod(2UL, modulus);
|
||
}
|
||
|
||
states[idx] = s;
|
||
}
|
||
|
||
private static void Kernel(Index1D index, ulong exponent, GpuUInt128 modulus, ArrayView<GpuUInt128> state)
|
||
{
|
||
// Lucas–Lehmer iteration in the field GF(2^p-1).
|
||
// For p < 128, use a Mersenne-specific squaring + reduction to avoid
|
||
// the generic 128-bit long-division-like reduction.
|
||
var s = new GpuUInt128(0UL, 4UL);
|
||
ulong i = 0UL, limit = exponent - 2UL;
|
||
if (exponent < 128UL)
|
||
{
|
||
for (; i < limit; i++)
|
||
{
|
||
s = SquareModMersenne128(s, exponent);
|
||
s.SubMod(2UL, modulus);
|
||
}
|
||
}
|
||
else
|
||
{
|
||
for (; i < limit; i++)
|
||
{
|
||
s.SquareMod(modulus);
|
||
s.SubMod(2UL, modulus);
|
||
}
|
||
}
|
||
|
||
state[0] = s;
|
||
}
|
||
|
||
// Squares a 128-bit value and reduces modulo M_p = 2^p - 1 using
|
||
// Mersenne folding. Valid for 0 < p < 128 and input s in [0, M_p].
|
||
private static GpuUInt128 SquareModMersenne128(GpuUInt128 s, ulong p)
|
||
{
|
||
// Full square: (H*2^64 + L)^2 = H^2*2^128 + 2HL*2^64 + L^2
|
||
SquareFull128(s, out var q3, out var q2, out var q1, out var q0);
|
||
|
||
// v = low128 + high128 (fold by 128 bits once)
|
||
var vHigh = new GpuUInt128(q3, q2);
|
||
var vLow = new GpuUInt128(q1, q0);
|
||
vLow.Add(vHigh);
|
||
|
||
// Mask to keep only p low bits and fold the carry bits (v >> p)
|
||
int topBits = (int)p.Mod128();
|
||
if (topBits == 0)
|
||
{
|
||
topBits = 128;
|
||
}
|
||
|
||
ulong maskLow = topBits >= 64 ? ulong.MaxValue : (1UL << topBits) - 1UL;
|
||
ulong maskHigh = topBits > 64 ? (1UL << (topBits - 64)) - 1UL : 0UL;
|
||
|
||
var carryBits = vLow >> topBits;
|
||
vLow = new(vLow.High & maskHigh, vLow.Low & maskLow);
|
||
|
||
// Propagate carryBits back into the masked value (single-limb fold)
|
||
GpuUInt128 before;
|
||
while (!carryBits.IsZero)
|
||
{
|
||
before = vLow;
|
||
vLow.Add(carryBits);
|
||
carryBits = vLow.CompareTo(before) < 0 ? GpuUInt128.One : GpuUInt128.Zero;
|
||
}
|
||
|
||
// Final correction if v >= modulus (mask)
|
||
if (vLow.High > maskHigh || (vLow.High == maskHigh && vLow.Low >= maskLow))
|
||
{
|
||
ulong borrow = 0UL;
|
||
ulong newLow = vLow.Low - maskLow;
|
||
borrow = vLow.Low < maskLow ? 1UL : 0UL;
|
||
ulong newHigh = vLow.High - maskHigh - borrow;
|
||
vLow = new GpuUInt128(newHigh, newLow);
|
||
}
|
||
|
||
return vLow;
|
||
}
|
||
|
||
// Helper: 128-bit square -> 256-bit product as four 64-bit limbs (q3..q0)
|
||
private static void SquareFull128(GpuUInt128 value, out ulong q3, out ulong q2, out ulong q1, out ulong q0)
|
||
{
|
||
ulong L = value.Low;
|
||
ulong H = value.High;
|
||
Mul64Parts(L, L, out var hLL, out var lLL); // L^2
|
||
Mul64Parts(H, H, out var hHH, out var lHH); // H^2
|
||
Mul64Parts(L, H, out var hLH, out var lLH); // L*H
|
||
|
||
// double LH
|
||
ulong dLH_low = lLH << 1;
|
||
ulong carry = (lLH >> 63) & 1UL;
|
||
ulong dLH_high = (hLH << 1) | carry;
|
||
|
||
q0 = lLL;
|
||
ulong sum1 = hLL + dLH_low;
|
||
ulong c1 = sum1 < hLL ? 1UL : 0UL;
|
||
q1 = sum1;
|
||
|
||
ulong sum2 = lHH + dLH_high;
|
||
ulong c2 = sum2 < lHH ? 1UL : 0UL;
|
||
sum2 += c1;
|
||
if (sum2 < c1)
|
||
{
|
||
c2++;
|
||
}
|
||
q2 = sum2;
|
||
q3 = hHH + c2;
|
||
}
|
||
|
||
// 64x64 -> 128 multiply (high,low)
|
||
[MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
|
||
private static void Mul64Parts(ulong a, ulong b, out ulong high, out ulong low)
|
||
{
|
||
ulong a0 = (uint)a;
|
||
ulong a1 = a >> 32;
|
||
ulong b0 = (uint)b;
|
||
ulong b1 = b >> 32;
|
||
|
||
ulong lo = a0 * b0;
|
||
ulong mid1 = a1 * b0;
|
||
ulong mid2 = a0 * b1;
|
||
ulong hi = a1 * b1;
|
||
|
||
ulong carry = (lo >> 32) + (uint)mid1 + (uint)mid2;
|
||
low = (lo & 0xFFFFFFFFUL) | (carry << 32);
|
||
hi += (mid1 >> 32) + (mid2 >> 32) + (carry >> 32);
|
||
high = hi;
|
||
}
|
||
|
||
[MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.AggressiveInlining)]
|
||
private static ulong ModPow64(ulong value, ulong exponent, ulong modulus)
|
||
{
|
||
ulong result = 1UL;
|
||
ulong baseValue = value % modulus;
|
||
ulong exp = exponent;
|
||
|
||
while (exp != 0UL)
|
||
{
|
||
if ((exp & 1UL) != 0UL)
|
||
{
|
||
result = (ulong)(((UInt128)result * baseValue) % modulus);
|
||
}
|
||
|
||
baseValue = (ulong)(((UInt128)baseValue * baseValue) % modulus);
|
||
exp >>= 1;
|
||
}
|
||
|
||
return result;
|
||
}
|
||
}
|
||
|