Pre-calculate SquareBits and place them in a static array

src/Lynx.Benchmark/PieceAtSquare_Benchmark.cs

@@ -227,7 +227,7 @@ private static int PieceAt_KnowingColor(Position position, int targetSquare)
     /// <returns></returns>
     private static int PieceAt(Position position, int targetSquare)
     {
-        var bit = BitBoardExtensions.SquareBit(targetSquare);
+        var bit = Constants.SquareBits[targetSquare];
 
         Side color;
 

src/Lynx.Benchmark/SquareBit_Benchmark.cs

@@ -0,0 +1,71 @@
+/*
+ *
+ *
+ */
+
+using BenchmarkDotNet.Attributes;
+using Lynx.Model;
+
+namespace Lynx.Benchmark;
+
+file static class BitBoardHelpers
+{
+    public static readonly ulong[] SquareBitsArray =
+        Enum.GetValuesAsUnderlyingType<BoardSquare>()
+            .OfType<int>()
+            .Select(square => 1UL << square)
+            .ToArray();
+
+    public static ulong CaculateSquareBit(int boardSquare)
+    {
+        return 1UL << boardSquare;
+    }
+}
+
+public class SquareBit_Benchmark : BaseBenchmark
+{
+    [Params(1, 10, 100, 1_000, 10_000)]
+    public int Size { get; set; }
+
+    private BoardSquare[] _squares = null!;
+
+    [GlobalSetup]
+    public void Setup()
+    {
+        _squares = Enumerable.Range((int)BoardSquare.a1, (int)BoardSquare.h8).
+            Select(_ => (BoardSquare)Random.Shared.Next((int)BoardSquare.a1, (int)BoardSquare.h8))
+            .ToArray();
+    }
+
+    [Benchmark(Baseline = true)]
+    public ulong Calculated()
+    {
+        ulong count = 0;
+
+        for (int i = 0; i < Size; ++i)
+        {
+            foreach (var square in _squares)
+            {
+                count += BitBoardHelpers.CaculateSquareBit((int)square);
+            }
+        }
+
+        return count;
+    }
+
+    [Benchmark]
+    public ulong Array()
+    {
+        ulong count = 0;
+
+        for (int i = 0; i < Size; ++i)
+        {
+            foreach (var square in _squares)
+            {
+                count += BitBoardHelpers.SquareBitsArray[(int)square];
+            }
+        }
+
+        return count;
+    }
+}

src/Lynx/Constants.cs

@@ -217,7 +217,6 @@ public static class Constants
     public const string WhiteLongCastle = "e1c1";
     public const string BlackLongCastle = "e8c8";
 
-
     public static readonly int[] EnPassantCaptureSquares =
     [
         0, 0, 0, 0, 0, 0, 0, 0,     //  0-7
@@ -301,6 +300,14 @@ public static class Constants
     ];
 
     public const int AbsoluteMaxDepth = 255;
+
+    /// <summary>
+    /// Bits that represents each square on a bitboard
+    /// </summary>
+    public static readonly ulong[] SquareBits = Enum.GetValuesAsUnderlyingType<BoardSquare>()
+        .OfType<int>()
+        .Select(square => 1UL << square)
+        .ToArray();
 }
 
 #pragma warning restore IDE0055

src/Lynx/Model/BitBoard.cs

@@ -167,26 +167,16 @@ public static int CountBits(this BitBoard board)
         return BitOperations.PopCount(board);
     }
 
-    /// <summary>
-    /// Extracts the bit that represents each square on a bitboard
-    /// </summary>
-    /// <param name="boardSquare"></param>
-    /// <returns></returns>
-    public static ulong SquareBit(int boardSquare)
-    {
-        return 1UL << boardSquare;
-    }
-
     public static bool Contains(this BitBoard board, int boardSquare)
     {
-        var bit = SquareBit(boardSquare);
+        var bit = Constants.SquareBits[boardSquare];
 
         return (board & bit) != default;
     }
 
     public static bool DoesNotContain(this BitBoard board, int boardSquare)
     {
-        var bit = SquareBit(boardSquare);
+        var bit = Constants.SquareBits[boardSquare];
 
         return (board & bit) == default;
     }

src/Lynx/Model/Position.cs

@@ -597,7 +597,7 @@ public string FEN(int halfMovesWithoutCaptureOrPawnMove = 0, int fullMoveClock =
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public int PieceAt(int square)
     {
-        var bit = BitBoardExtensions.SquareBit(square);
+        var bit = Constants.SquareBits[square];
 
         Side color;
 

src/Lynx/SEE.cs

@@ -55,8 +55,8 @@ public static bool IsGoodCapture(Position position, Move move, int threshold = 0
         var targetSquare = move.TargetSquare();
 
         var occupancy = position.OccupancyBitBoards[(int)Side.Both]
-            ^ BitBoardExtensions.SquareBit(move.SourceSquare())
-            ^ BitBoardExtensions.SquareBit(targetSquare);
+            ^ Constants.SquareBits[move.SourceSquare()]
+            ^ Constants.SquareBits[targetSquare];
 
         var queens = position.Queens;
         var bishops = queens | position.Bishops;
@@ -145,8 +145,8 @@ public static bool HasPositiveScore(Position position, Move move, int threshold
         var targetSquare = move.TargetSquare();
 
         var occupancy = position.OccupancyBitBoards[(int)Side.Both]
-            ^ BitBoardExtensions.SquareBit(move.SourceSquare())
-            ^ BitBoardExtensions.SquareBit(targetSquare);
+            ^ Constants.SquareBits[move.SourceSquare()]
+            ^ Constants.SquareBits[targetSquare];
 
         var queens = position.Queens;
         var bishops = queens | position.Bishops;