Replace status modulo with subtract loop

PerfectNumbers.Core/Cpu/MersenneNumberDivisorByDivisorCpuTester.cs

@@ -80,9 +80,9 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
             return true;
         }
 
-        ulong processedCount;
+        ulong processedCount = 0UL;
-        ulong lastProcessed;
+        ulong lastProcessed = 0UL;
-        bool processedAll;
+        bool processedAll = false;
 
         bool composite = CheckDivisors(
             prime,
@@ -238,20 +238,19 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
                     }
                 }
 
-				if (divisorCycle != 0 && divisorCycle == prime)
+                if (divisorCycle == prime)
                 {
+                    // A cycle equal to the tested exponent (which is prime in this path)
+                    // guarantees that the candidate divides the corresponding Mersenne
+                    // number because the order of 2 modulo the divisor is exactly p.
                     processedAll = true;
                     return true;
                 }
-				else if (divisorCycle == 0)
+
+                if (divisorCycle == 0UL)
                 {
-					Console.WriteLine($"Divisor cycle wasn't calculated for ${prime}");
+                    Console.WriteLine($"Divisor cycle was not calculated for {prime}");
                 }
-				// if (divisorCycle != 0UL && CheckDivisor(prime, divisorCycle, divisorData) != 0)
-				// {
-				// 	processedAll = true;
-				// 	return true;
-				// }
             }
 
             divisor += step;
@@ -299,9 +298,16 @@ public sealed class MersenneNumberDivisorByDivisorCpuTester : IMersenneNumberDiv
         }
 
         ulong total = _lastStatusDivisor + processedCount;
-        // TODO: Replace this modulo with the ring-buffer style counter (subtract loop) used in the fast CLI
+        if (total >= interval)
-        // status benchmarks so we avoid `%` in this hot loop while still wrapping progress correctly.
+        {
-        _lastStatusDivisor = total % interval;
+            do
+            {
+                total -= interval;
+            }
+            while (total >= interval);
+        }
+
+        _lastStatusDivisor = total;
     }
 
     private static ulong ComputeDivisorLimitFromMaxPrime(ulong maxPrime)