Refine by-divisor prime test time limits

PerfectNumbers.Core/PrimeTestTimeLimit.cs

@@ -0,0 +1,72 @@
+using System;
+using System.Diagnostics;
+
+namespace PerfectNumbers.Core;
+
+internal readonly struct PrimeTestTimeLimit
+{
+    private readonly long _deadlineTimestamp;
+
+    private PrimeTestTimeLimit(bool isActive, long deadlineTimestamp)
+    {
+        IsActive = isActive;
+        _deadlineTimestamp = deadlineTimestamp;
+    }
+
+    internal bool IsActive { get; }
+
+    internal static bool TryCreate(TimeSpan? timeLimit, out PrimeTestTimeLimit limit)
+    {
+        if (!timeLimit.HasValue)
+        {
+            limit = new PrimeTestTimeLimit(isActive: false, deadlineTimestamp: long.MaxValue);
+            return true;
+        }
+
+        TimeSpan limitValue = timeLimit.GetValueOrDefault();
+        if (limitValue <= TimeSpan.Zero)
+        {
+            limit = new PrimeTestTimeLimit(isActive: true, deadlineTimestamp: long.MinValue);
+            return false;
+        }
+
+        double seconds = limitValue.TotalSeconds;
+        if (double.IsInfinity(seconds))
+        {
+            limit = new PrimeTestTimeLimit(isActive: true, deadlineTimestamp: long.MaxValue);
+            return true;
+        }
+
+        double scaled = seconds * Stopwatch.Frequency;
+        long limitTicks = scaled >= long.MaxValue ? long.MaxValue : (long)scaled;
+        long startTimestamp = Stopwatch.GetTimestamp();
+        long deadline = startTimestamp <= long.MaxValue - limitTicks ? startTimestamp + limitTicks : long.MaxValue;
+        if (deadline < startTimestamp)
+        {
+            deadline = long.MaxValue;
+        }
+
+        limit = new PrimeTestTimeLimit(isActive: true, deadlineTimestamp: deadline);
+        return true;
+    }
+
+    internal bool HasExpired()
+    {
+        if (!IsActive)
+        {
+            return false;
+        }
+
+        if (_deadlineTimestamp == long.MaxValue)
+        {
+            return false;
+        }
+
+        if (_deadlineTimestamp == long.MinValue)
+        {
+            return true;
+        }
+
+        return Stopwatch.GetTimestamp() >= _deadlineTimestamp;
+    }
+}