Add benchmarks

Solver/Crafty/Solver.cs

@@ -99,23 +99,45 @@ public class Solver
 
     [Pure]
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
-    // https://stackoverflow.com/a/23592221
-    private static (int, uint) HMaxIndex(Vector256<float> v, int len)
+    public static int HMaxIndexScalar(Vector<float> v, int len)
     {
-        var vfilt = Avx.Blend(v, Vector256<float>.Zero, (byte)~((1 << len) - 1));
+        var m = 0;
+        for (var i = 1; i < len; ++i)
+        {
+            if (v[i] >= v[m])
+                m = i;
+        }
+        return m;
+    }
 
+    [Pure]
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    // https://stackoverflow.com/a/23592221
+    public static int HMaxIndexAVX2(Vector<float> v, int len)
+    {
+        // Remove NaNs
+        var vfilt = Avx.Blend(v.AsVector256(), Vector256<float>.Zero, (byte)~((1 << len) - 1));
+
+        // Find max value and broadcast to all lanes
         var vmax128 = HMax(vfilt);
         var vmax = Vector256.Create(vmax128, vmax128);
 
-        var vcmp = Avx.CompareEqual(v, vmax);
+        // Find the highest index with that value, respecting len
+        var vcmp = Avx.CompareEqual(vfilt, vmax);
         var mask = unchecked((uint)Avx2.MoveMask(vcmp.AsByte()));
-        mask <<= (8 - len) << 2;
 
-        var inverseIdx = BitOperations.LeadingZeroCount(mask) >> 2;
+        var inverseIdx = BitOperations.LeadingZeroCount(mask << ((8 - len) << 2)) >> 2;
 
-        return (len - 1 - inverseIdx, mask);
+        return len - 1 - inverseIdx;
     }
 
+    [Pure]
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    private static int HMaxIndex(Vector<float> v, int len) =>
+        Avx2.IsSupported ?
+        HMaxIndexAVX2(v, len) :
+        HMaxIndexScalar(v, len);
+
     [Pure]
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     private Node EvalBestChild(float parentVisits, ReadOnlySpan<Node> children)
@@ -134,7 +156,6 @@ public class Solver
         
         var max = 0;
         var maxScore = 0f;
-
         for (var i = 0; i < length; i += vecLength)
         {
             var iterCount = i + vecLength > length ?
@@ -153,7 +174,7 @@ public class Solver
             var exploration = Vector.SquareRoot(CVector / new Vector<float>(visits));
             var evalScores = exploitation + exploration;
 
-            var (idx, mask) = HMaxIndex(evalScores.AsVector256(), iterCount);
+            var idx = HMaxIndex(evalScores, iterCount);
             
             if (evalScores[idx] >= maxScore)
             {
@@ -186,7 +207,7 @@ public class Solver
         if (initialState.IsComplete)
             return (initialNode, initialState.CompletionState, initialState.CalculateScore(Config.MaxStepCount) ?? 0);
 
-        var randomAction = initialState.AvailableActions.SelectRandom(Random);
+        var randomAction = initialState.AvailableActions.First();//.SelectRandom(Random);
         initialState.AvailableActions.RemoveAction(randomAction);
         var expandedNode = initialNode.Add(Execute(initialState.State, randomAction, true));
 
@@ -201,7 +222,7 @@ public class Solver
         {
             if (SimulationNode.GetCompletionState(currentCompletionState, currentActions) != CompletionState.Incomplete)
                 break;
-            randomAction = currentActions.SelectRandom(Random);
+            randomAction = currentActions.First();//.SelectRandom(Random);
             actions[actionCount++] = randomAction;
             (_, currentState) = Simulator.Execute(currentState, randomAction);
             currentCompletionState = Simulator.CompletionState;