Initial commit.

PerfectNumbers.Core/Cpu/MersenneNumberIncrementalCpuTester.cs

@@ -0,0 +1,83 @@
+namespace PerfectNumbers.Core.Cpu;
+
+public class MersenneNumberIncrementalCpuTester(GpuKernelType kernelType)
+{
+	private static readonly MersenneDivisorCycles _cycles = MersenneDivisorCycles.Shared;
+	private readonly GpuKernelType _kernelType = kernelType;
+
+	public void Scan(ulong exponent, UInt128 twoP, bool lastIsSeven, UInt128 maxK, ref bool isPrime)
+	{
+		UInt128 k, one = k = UInt128.One;
+		ulong divMul = (ulong)((((UInt128)1 << 64) - UInt128.One) / exponent) + 1UL;
+		// Use residue automaton always on CPU
+		var auto = new MersenneResidueAutomaton(exponent);
+
+		bool reject, shouldCheck;
+		UInt128 q = auto.CurrentQ(),
+				divPow, halfPow, phi, qCycle;
+
+		ulong div, mod8, phi64;
+
+		while (k <= maxK && Volatile.Read(ref isPrime))
+		{
+			qCycle = MersenneDivisorCycles.GetCycle(q);
+			shouldCheck = lastIsSeven
+				? (auto.Mod10R != 5UL)
+				: (auto.Mod10R != 5UL);
+			if (shouldCheck)
+			{
+				mod8 = auto.Mod8R;
+				if (mod8 != 1UL && mod8 != 7UL)
+				{
+					shouldCheck = false;
+				}
+				else if (auto.Mod3R == 0UL || auto.Mod5R == 0UL)
+				{
+					shouldCheck = false;
+				}
+			}
+
+			if (shouldCheck)
+			{
+				if (_kernelType == GpuKernelType.Pow2Mod)
+				{
+					reject = exponent.PowModWithCycle(q, qCycle) == UInt128.One;
+				}
+				else
+				{
+					phi = q - one;
+					reject = false;
+					if (phi <= ulong.MaxValue)
+					{
+						phi64 = (ulong)phi;
+						if (phi64.PowModWithCycle(q, qCycle) == one)
+						{
+							halfPow = (phi64 >> 1).PowModWithCycle(q, qCycle) - one;
+							if (halfPow.BinaryGcd(q) == one)
+							{
+								div = phi64.FastDiv64(exponent, divMul);
+								divPow = div.PowModWithCycle(q, qCycle) - one;
+								if (divPow.BinaryGcd(q) == one)
+								{
+									reject = true;
+								}
+							}
+						}
+					}
+				}
+
+				if (reject && q.IsPrimeCandidate())
+				{
+					Volatile.Write(ref isPrime, false);
+					break;
+				}
+			}
+
+			k += 1UL;
+			auto.Next();
+			q = auto.CurrentQ();
+		}
+
+		return;
+	}
+}