From 5ce67fa1c59aaeacdf3a05f3961a80328b5b4449 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marek=20Lema=C5=84czyk?= <marek@lemanczyk.eu>
Date: Tue, 23 Sep 2025 23:28:32 +0200
Subject: [PATCH] Reduce span slicing in GPU divisor checks

---
 ...MersenneNumberDivisorByDivisorGpuTester.cs | 54 +++++++++++--------
 1 file changed, 32 insertions(+), 22 deletions(-)

diff --git a/PerfectNumbers.Core/Gpu/MersenneNumberDivisorByDivisorGpuTester.cs b/PerfectNumbers.Core/Gpu/MersenneNumberDivisorByDivisorGpuTester.cs
index 0d6175c..d5a0c28 100644
--- a/PerfectNumbers.Core/Gpu/MersenneNumberDivisorByDivisorGpuTester.cs
+++ b/PerfectNumbers.Core/Gpu/MersenneNumberDivisorByDivisorGpuTester.cs
@@ -322,11 +322,23 @@ public sealed class MersenneNumberDivisorByDivisorGpuTester
 			MersenneDivisorCycles? divisorCycles = useCycles ? MersenneDivisorCycles.Shared : null;
 			ulong cycle = useCycles ? divisorCycles!.GetCycle(divisor) : 0UL;
 			MontgomeryDivisorData divisorData = CreateMontgomeryDivisorData(divisor);
-			while (offset < primes.Length)
-			{
-				int batchSize = Math.Min(_owner._gpuBatchSize, primes.Length - offset);
-				Span<ulong> primeSpan = _primesHost.AsSpan(0, batchSize);
-				primes.Slice(offset, batchSize).CopyTo(primeSpan);
+                        Span<ulong> primeSpan = _primesHost.AsSpan(0, _owner._gpuBatchSize);
+                        Span<int> indexSpan = _indexHost.AsSpan(0, _owner._gpuBatchSize);
+                        Span<byte> hitSpan = _hitsHost.AsSpan(0, _owner._gpuBatchSize);
+                        int currentSpanSize = _owner._gpuBatchSize;
+
+                        while (offset < primes.Length)
+                        {
+                                int batchSize = Math.Min(_owner._gpuBatchSize, primes.Length - offset);
+                                if (batchSize != currentSpanSize)
+                                {
+                                        primeSpan = _primesHost.AsSpan(0, batchSize);
+                                        indexSpan = _indexHost.AsSpan(0, batchSize);
+                                        hitSpan = _hitsHost.AsSpan(0, batchSize);
+                                        currentSpanSize = batchSize;
+                                }
+
+                                primes.Slice(offset, batchSize).CopyTo(primeSpan);
 
 				if (++consoleStatus == PerfectNumberConstants.ConsoleInterval)
 				{
@@ -334,13 +346,11 @@ public sealed class MersenneNumberDivisorByDivisorGpuTester
 					consoleStatus = 0;
 				}
 
-				Span<int> indexSpan = _indexHost.AsSpan(0, batchSize);
-				Span<byte> hitSpan = _hitsHost.AsSpan(0, batchSize);
-				Span<byte> hitsSlice = hits.Slice(offset, batchSize);
-				int gpuCount = 0;
+                                Span<byte> hitsSlice = hits.Slice(offset, batchSize);
+                                int gpuCount = 0;
 
-				if (useCycles)
-				{
+                                if (useCycles)
+                                {
 					for (int i = 0; i < batchSize; i++)
 					{
 						ulong primeValue = primeSpan[i];
@@ -357,19 +367,19 @@ public sealed class MersenneNumberDivisorByDivisorGpuTester
 
 					if (gpuCount > 0)
 					{
-						var primesView = _primesBuffer.View.SubView(0, gpuCount);
-						var hitsView = _hitsBuffer.View.SubView(0, gpuCount);
+                                                var primesView = _primesBuffer.View.SubView(0, gpuCount);
+                                                var hitsView = _hitsBuffer.View.SubView(0, gpuCount);
 
-						primesView.CopyFromCPU(ref MemoryMarshal.GetReference(primeSpan.Slice(0, gpuCount)), gpuCount);
-						_kernel(gpuCount, divisorData, primesView, hitsView);
-						_accelerator.Synchronize();
+                                                primesView.CopyFromCPU(ref MemoryMarshal.GetReference(primeSpan), gpuCount);
+                                                _kernel(gpuCount, divisorData, primesView, hitsView);
+                                                _accelerator.Synchronize();
 
-						hitsView.CopyToCPU(ref MemoryMarshal.GetReference(hitSpan.Slice(0, gpuCount)), gpuCount);
-						for (int i = 0; i < gpuCount; i++)
-						{
-							hitsSlice[indexSpan[i]] = hitSpan[i];
-						}
-					}
+                                                hitsView.CopyToCPU(ref MemoryMarshal.GetReference(hitSpan), gpuCount);
+                                                for (int i = 0; i < gpuCount; i++)
+                                                {
+                                                        hitsSlice[indexSpan[i]] = hitSpan[i];
+                                                }
+                                        }
 				}
 				else
 				{