--gpu-ration command-line argument added. AscendingDivisorRemainderStepper implemented in PrimeTester.IsPrimeCpu. PrimeOrderCalculator.RunOnCpu adjusted for low GPU ratios to prevent infinite increase of the counter.

PerfectNumbers.Core/AscendingDivisorRemainderStepper.cs

@@ -0,0 +1,38 @@
+using System.Runtime.CompilerServices;
+
+namespace PerfectNumbers.Core;
+
+public struct AscendingDivisorRemainderStepper
+{
+    private readonly ulong dividend;
+    private ulong maxDivisor;
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public AscendingDivisorRemainderStepper(ulong value)
+    {
+        dividend = value;
+        ulong root = (ulong)Math.Sqrt(value);
+        if ((UInt128)root * root < value)
+        {
+            root++;
+        }
+
+        maxDivisor = root;
+    }
+
+	[MethodImpl(MethodImplOptions.AggressiveInlining)]
+	public readonly bool ShouldContinue(ulong divisor) => divisor <= maxDivisor;
+
+	[MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public bool Divides(ulong divisor)
+    {
+        ulong quotient = dividend / divisor;
+        ulong remainder = dividend - (quotient * divisor);
+        if (quotient < maxDivisor)
+        {
+            maxDivisor = quotient;
+        }
+
+        return remainder == 0UL;
+    }
+}