Initial commit.

PerfectNumbers.Core/KRangeFinder.cs

@@ -0,0 +1,79 @@
+using PeterO.Numbers;
+
+namespace PerfectNumbers.Core;
+
+public static class KRangeFinder
+{
+    public static (int? Min, int? Max) FindForPrime(ERational alphaM, EInteger p, int kStart, int kEnd)
+    {
+        int? min = null;
+        int? max = null;
+        for (int k = kStart; k <= kEnd; k++)
+        {
+            ERational aP = AlphaCalculations.ComputeAlphaP(p, k);
+            ERational prod = aP.Multiply(alphaM);
+            int cmp = prod.CompareTo(RationalNumbers.Two);
+            if (cmp == 0)
+            {
+                if (min == null || k < min)
+                {
+                    min = k;
+                }
+                if (max == null || k > max)
+                {
+                    max = k;
+                }
+            }
+            if (cmp < 0)
+            {
+                break;
+            }
+        }
+        return (min, max);
+    }
+
+    public static bool TryFindForPrime(ERational alphaM, EInteger p, out int? min, out int? max, int kStart, int kEnd)
+    {
+        (min, max) = FindForPrime(alphaM, p, kStart, kEnd);
+        return min.HasValue && max.HasValue && min.Value <= max.Value;
+    }
+
+    public static (int? Min, int? Max) Find(ERational alphaM, EInteger pMin, EInteger pMax, int kStart, int kEnd, PrimeCache primes)
+    {
+        int? min = null;
+        int? max = null;
+        EInteger[] eulerPrimes = primes.GetEulerPrimes(pMin, pMax);
+        object sync = new();
+        Parallel.For(
+            0,
+            eulerPrimes.Length,
+            new ParallelOptions { MaxDegreeOfParallelism = Environment.ProcessorCount },
+            i =>
+            {
+                (int? localMin, int? localMax) = FindForPrime(alphaM, eulerPrimes[i], kStart, kEnd);
+                if (localMin == null)
+                {
+                    return;
+                }
+                lock (sync)
+                {
+                    if (min == null || localMin < min)
+                    {
+                        min = localMin;
+                    }
+                    if (max == null || localMax > max)
+                    {
+                        max = localMax;
+                    }
+                }
+            });
+        return (min, max);
+    }
+
+    public static bool TryFind(ERational alphaM, EInteger pMin, EInteger pMax, out int? min, out int? max, int kStart, int kEnd, PrimeCache primes)
+    {
+        (min, max) = Find(alphaM, pMin, pMax, kStart, kEnd, primes);
+        return min.HasValue && max.HasValue && min.Value <= max.Value;
+    }
+}
+