Streamline GPU remainder batching tables

PerfectNumbers.Core/Gpu/MersenneNumberDivisorRemainderGpuStepper.cs

@@ -8,50 +8,44 @@ namespace PerfectNumbers.Core.Gpu;
 
 internal sealed class MersenneNumberDivisorRemainderGpuStepper : IDisposable
 {
+    private const int RemainderCount = 6;
+
     private readonly GpuContextPool.GpuContextLease _lease;
     private readonly Accelerator _accelerator;
-    private readonly Action<Index1D, int, ArrayView<byte>, ArrayView<byte>, ArrayView<byte>, ArrayView<byte>> _kernel;
+    private readonly Action<Index1D, int, ArrayView<byte>, ArrayView<byte>, ArrayView<byte>> _kernel;
     private MemoryBuffer1D<byte, Stride1D.Dense> _remainderBuffer;
     private MemoryBuffer1D<byte, Stride1D.Dense> _stepBuffer;
-    private MemoryBuffer1D<byte, Stride1D.Dense> _modulusBuffer;
     private MemoryBuffer1D<byte, Stride1D.Dense> _resultBuffer;
     private byte[] _hostRemainders;
     private byte[] _hostSteps;
-    private byte[] _hostModuli;
     private readonly int _length;
     private int _capacity;
     private bool _disposed;
 
-    internal MersenneNumberDivisorRemainderGpuStepper(ReadOnlySpan<byte> steps, ReadOnlySpan<byte> moduli)
+    internal MersenneNumberDivisorRemainderGpuStepper(ReadOnlySpan<byte> steps)
     {
-        if (steps.Length != moduli.Length)
+        if (steps.Length != RemainderCount)
         {
-            throw new ArgumentException("Steps and moduli must have the same length.");
+            throw new ArgumentException("Step table must contain exactly six entries.");
         }
 
         _lease = GpuContextPool.RentPreferred(preferCpu: false);
         _accelerator = _lease.Accelerator;
-        _kernel = _accelerator.LoadAutoGroupedStreamKernel<Index1D, int, ArrayView<byte>, ArrayView<byte>, ArrayView<byte>, ArrayView<byte>>(AdvanceRemaindersKernel);
+        _kernel = _accelerator.LoadAutoGroupedStreamKernel<Index1D, int, ArrayView<byte>, ArrayView<byte>, ArrayView<byte>>(AdvanceRemaindersKernel);
 
         _length = steps.Length;
         _capacity = Math.Max(1, _length);
         _remainderBuffer = _accelerator.Allocate1D<byte>(_capacity);
         _stepBuffer = _accelerator.Allocate1D<byte>(_capacity);
-        _modulusBuffer = _accelerator.Allocate1D<byte>(_capacity);
         _resultBuffer = _accelerator.Allocate1D<byte>(_capacity);
 
         _hostRemainders = ArrayPool<byte>.Shared.Rent(_capacity);
         _hostSteps = ArrayPool<byte>.Shared.Rent(_capacity);
-        _hostModuli = ArrayPool<byte>.Shared.Rent(_capacity);
 
         steps.CopyTo(_hostSteps.AsSpan(0, _length));
-        moduli.CopyTo(_hostModuli.AsSpan(0, _length));
 
         ArrayView1D<byte, Stride1D.Dense> stepView = _stepBuffer.View.SubView(0, _length);
         stepView.CopyFromCPU(ref MemoryMarshal.GetReference(_hostSteps.AsSpan(0, _length)), _length);
-
-        ArrayView1D<byte, Stride1D.Dense> modulusView = _modulusBuffer.View.SubView(0, _length);
-        modulusView.CopyFromCPU(ref MemoryMarshal.GetReference(_hostModuli.AsSpan(0, _length)), _length);
     }
 
     public void Dispose()
@@ -64,11 +58,9 @@ internal sealed class MersenneNumberDivisorRemainderGpuStepper : IDisposable
         _disposed = true;
         _remainderBuffer.Dispose();
         _stepBuffer.Dispose();
-        _modulusBuffer.Dispose();
         _resultBuffer.Dispose();
         ArrayPool<byte>.Shared.Return(_hostRemainders, clearArray: false);
         ArrayPool<byte>.Shared.Return(_hostSteps, clearArray: false);
-        ArrayPool<byte>.Shared.Return(_hostModuli, clearArray: false);
         _lease.Dispose();
     }
 
@@ -96,16 +88,15 @@ internal sealed class MersenneNumberDivisorRemainderGpuStepper : IDisposable
         remainderView.CopyFromCPU(ref MemoryMarshal.GetReference(hostRemainderSpan), _length);
 
         ArrayView1D<byte, Stride1D.Dense> stepView = _stepBuffer.View.SubView(0, _length);
-        ArrayView1D<byte, Stride1D.Dense> modulusView = _modulusBuffer.View.SubView(0, _length);
         ArrayView1D<byte, Stride1D.Dense> resultView = _resultBuffer.View.SubView(0, _length);
 
-        _kernel(_length, advanceCount, remainderView, stepView, modulusView, resultView);
+        _kernel(_length, advanceCount, remainderView, stepView, resultView);
 
         resultView.CopyToCPU(ref MemoryMarshal.GetReference(hostRemainderSpan), _length);
         hostRemainderSpan.CopyTo(remainders);
     }
 
-    private static void AdvanceRemaindersKernel(Index1D index, int advanceCount, ArrayView<byte> remainders, ArrayView<byte> steps, ArrayView<byte> moduli, ArrayView<byte> results)
+    private static void AdvanceRemaindersKernel(Index1D index, int advanceCount, ArrayView<byte> remainders, ArrayView<byte> steps, ArrayView<byte> results)
     {
         int idx = index;
         if (idx >= remainders.Length)
@@ -113,7 +104,7 @@ internal sealed class MersenneNumberDivisorRemainderGpuStepper : IDisposable
             return;
         }
 
-        int modulus = moduli[idx];
+        int modulus = GetModulus(idx);
         if (modulus == 0)
         {
             results[idx] = remainders[idx];
@@ -132,4 +123,18 @@ internal sealed class MersenneNumberDivisorRemainderGpuStepper : IDisposable
 
         results[idx] = (byte)adjusted;
     }
+
+    private static int GetModulus(int index)
+    {
+        return index switch
+        {
+            0 => 10,
+            1 => 8,
+            2 => 5,
+            3 => 3,
+            4 => 7,
+            5 => 11,
+            _ => 0,
+        };
+    }
 }