Initial commit.

PerfectNumbers.Core/PowerCache.cs

@@ -0,0 +1,65 @@
+using System.Collections.Concurrent;
+using System.Numerics;
+using PeterO.Numbers;
+
+namespace PerfectNumbers.Core;
+
+public static class PowerCache
+{
+    private static readonly ConcurrentDictionary<ulong, BigInteger[]> BigCache = new();
+    private static readonly ConcurrentDictionary<EInteger, EInteger[]> ECache = new();
+
+    public static BigInteger Get(ulong baseVal, int exponent)
+    {
+        if (!BigCache.TryGetValue(baseVal, out var powers))
+        {
+            powers = new BigInteger[exponent + 1];
+            powers[0] = BigInteger.One;
+            BigCache[baseVal] = powers;
+        }
+
+        if (powers.Length <= exponent)
+        {
+            int oldLength = powers.Length;
+            Array.Resize(ref powers, exponent + 1);
+            for (int i = oldLength; i <= exponent; i++)
+                powers[i] = BigInteger.Zero;
+
+            BigCache[baseVal] = powers;
+        }
+
+        if (powers[exponent].IsZero)
+        {
+            for (int i = 1; i <= exponent; i++)
+                if (powers[i].IsZero)
+                    powers[i] = powers[i - 1] * baseVal;
+        }
+        
+        return powers[exponent];
+    }
+
+    public static EInteger Get(EInteger baseVal, int exponent)
+    {
+        if (!ECache.TryGetValue(baseVal, out var powers))
+        {
+            powers = new EInteger[exponent + 1];
+            powers[0] = EInteger.One;
+            ECache[baseVal] = powers;
+        }
+        if (powers.Length <= exponent)
+        {
+            int oldLength = powers.Length;
+            Array.Resize(ref powers, exponent + 1);
+            for (int i = oldLength; i <= exponent; i++)
+                powers[i] = null;
+            ECache[baseVal] = powers;
+        }
+        if (powers[exponent] == null)
+        {
+            for (int i = 1; i <= exponent; i++)
+                if (powers[i] == null)
+                    powers[i] = powers[i - 1]! * baseVal;
+        }
+        return powers[exponent]!;
+    }
+}