Revert "Merge pull request #251 from mlemanczyk/codex/refactor-prime-checking-on-gpu-n5t2pm"

This reverts commit 936ce239db, reversing
changes made to e14b77e504.

PerfectNumbers.Core/Gpu/MersenneNumberLucasLehmerGpuTester.cs

@@ -38,6 +38,16 @@ public class MersenneNumberLucasLehmerGpuTester
     // Configurable LL slice size to keep kernels short. Default 32.
     public int SliceSize = 32;
 
+    public bool IsMersennePrime(ulong exponent)
+    {
+        // Default to global kernel preference for backward compatibility.
+        bool runOnGpu = !GpuContextPool.ForceCpu;
+        // TODO: Inline this wrapper once callers request IsPrime directly so the Lucas–Lehmer fast path
+        // avoids an extra method frame; the LucasLehmerGpuBenchmarks showed the delegate hop shaving
+        // measurable time off tight reload loops when removed.
+        return IsPrime(exponent, runOnGpu);
+    }
+
     public bool IsPrime(ulong exponent, bool runOnGpu)
     {
         // Early rejections aligned with incremental/order sieves, but safe for small p:
@@ -68,7 +78,7 @@ public class MersenneNumberLucasLehmerGpuTester
         }
         else
         {
-            var gpu = GpuContextPool.Rent();
+            var gpu = GpuContextPool.RentPreferred(preferCpu: !runOnGpu);
             var accelerator = gpu.Accelerator;
             var kernel = GetKernel(accelerator);
             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.
@@ -100,7 +110,7 @@ public class MersenneNumberLucasLehmerGpuTester
             }
         }
 
-        var gpu = GpuContextPool.Rent();
+        var gpu = GpuContextPool.RentPreferred(preferCpu: false);
         var accelerator = gpu.Accelerator;
         var kernel = GetBatchKernel(accelerator);
 
@@ -152,7 +162,7 @@ public class MersenneNumberLucasLehmerGpuTester
 
     private bool IsMersennePrimeNtt(ulong exponent, GpuUInt128 nttMod, GpuUInt128 primitiveRoot, bool runOnGpu)
     {
-        var gpu = GpuContextPool.Rent();
+        var gpu = GpuContextPool.RentPreferred(preferCpu: !runOnGpu);
         var accelerator = gpu.Accelerator;
         var addKernel = GetAddSmallKernel(accelerator);
         var subKernel = GetSubSmallKernel(accelerator);