Merge branch 'main' into tt-quiescence

README.md

@@ -90,13 +90,28 @@ If you're a Linux user and are new to .NET ecosystem, the conversation in [this
 
 - Aspiration Windows [[1](https://web.archive.org/web/20071031095918/http://www.brucemo.com/compchess/programming/aspiration.htm)] [[2](https://www.chessprogramming.org/Aspiration_Windows)]
 
+- Transposition Table [[1](https://web.archive.org/web/20071031100051/http://www.brucemo.com/compchess/programming/hashing.htm)]
+
+- Check extensions [[1](https://www.chessprogramming.org/Check_Extensions)]
+
 ## Credits
 
 Lynx development wouldn't have been possible without:
 
+-  [`BitBoard Chess Engine in C` YouTube playlist](https://www.youtube.com/playlist?list=PLmN0neTso3Jxh8ZIylk74JpwfiWNI76Cs), where [@maksimKorzh](https://github.com/maksimKorzh) explains how he developed his [BBC](https://github.com/maksimKorzh/bbc) engine
+
 - [Chess Programming Wiki](https://www.chessprogramming.org/)
 
--  [`BitBoard Chess Engine in C` YouTube playlist](https://www.youtube.com/playlist?list=PLmN0neTso3Jxh8ZIylk74JpwfiWNI76Cs), where [@maksimKorzh](https://github.com/maksimKorzh) explains how he developed his [BBC](https://github.com/maksimKorzh/bbc) engine
+- Engine Programming discord group, especially Jamie Whiting
+([Akimbo](https://github.com/JacquesRW/akimbo)), Antares ([Altair](https://github.com/Alex2262/AltairChessEngine)), Ciekce ([Stormphrax](https://github.com/Ciekce/Stormphrax/)), Rak ([Mess](https://github.com/raklaptudirm/mess)), etc.
+
+- The community Discord around [SebLague/Chess-Challenge](https://github.com/SebLague/Chess-Challenge/), which allowed me to discover EP discord and to revisit the basics, this time explained by very knowledgeable developers (such as the ones above) to people without any previous chess engine programming knowledge
+
+- [Marcel Vanthoor's blog](https://rustic-chess.org/) about creating his engine Rustic
+
+- Countless other developers and online resources, who/which I should probably remember, but don't come to my mind right now
+
+Thanks also to all the testers that invest their time in computer chess, especially those ones that test lower rated engines (as opposed to only top ones).
 
 [buildlink]: https://github.com/lynx-chess/Lynx/actions/workflows/ci.yml
 [buildlogo]: https://github.com/lynx-chess/Lynx/actions/workflows/ci.yml/badge.svg

src/Lynx.Benchmark/FENGeneration.cs

@@ -2033,7 +2033,7 @@ public RecordStructCustomPosition(RecordStructCustomPosition position, Move move
         _fen = FENHelpers.UpdateSecondPartOfFEN(fenSb, Side, Castle, EnPassant);
     }
 
-    private string CalculateFEN()
+    private readonly string CalculateFEN()
     {
         var sb = new StringBuilder(100);
 

src/Lynx.Benchmark/MakeUnmakeMove_implementation.cs

@@ -33,6 +33,8 @@
  *  | MakeUnmakeMove_WithZobristKey | (rnbq(...)1, 4) [61] |  29.83 ms |  0.586 ms |  0.651 ms |  0.78 |    0.03 |   4781.2500 |    9.54 MB |        0.22 |
  */
 
+#pragma warning disable S101, S1854 // Types should be named in PascalCase
+
 using BenchmarkDotNet.Attributes;
 using Lynx.Model;
 using NLog;
@@ -777,7 +779,7 @@ public void UnMakeNullMove(MakeMoveGameState gameState)
         /// </summary>
         /// <returns></returns>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        internal bool IsValid()
+        internal readonly bool IsValid()
         {
             var kingBitBoard = PieceBitBoards[(int)Piece.K + Utils.PieceOffset(Side)];
             var kingSquare = kingBitBoard == default ? -1 : kingBitBoard.GetLS1BIndex();
@@ -796,7 +798,7 @@ internal bool IsValid()
         /// </summary>
         /// <returns></returns>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public bool WasProduceByAValidMove()
+        public readonly bool WasProduceByAValidMove()
         {
             var oppositeKingBitBoard = PieceBitBoards[(int)Piece.K + Utils.PieceOffset((Side)Utils.OppositeSide(Side))];
             var oppositeKingSquare = oppositeKingBitBoard == default ? -1 : oppositeKingBitBoard.GetLS1BIndex();
@@ -805,7 +807,7 @@ public bool WasProduceByAValidMove()
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public IEnumerable<Move> AllPossibleMoves(Move[]? movePool = null) => MakeMoveMoveGenerator.GenerateAllMoves(this, movePool);
+        public readonly IEnumerable<Move> AllPossibleMoves(Move[]? movePool = null) => MakeMoveMoveGenerator.GenerateAllMoves(this, movePool);
     }
 
     public readonly struct MakeMoveGameState
@@ -990,15 +992,13 @@ public static class MakeMoveMoveGenerator
             (int origin, BitBoard _) => MakeMoveAttacks.KnightAttacks[origin],
             (int origin, BitBoard occupancy) => MakeMoveAttacks.BishopAttacks(origin, occupancy),
             (int origin, BitBoard occupancy) => MakeMoveAttacks.RookAttacks(origin, occupancy),
-            // TODO try to improve performance by re-using bishop and rook attacks
             (int origin, BitBoard occupancy) => MakeMoveAttacks.QueenAttacks(origin, occupancy),
             (int origin, BitBoard _) => MakeMoveAttacks.KingAttacks[origin],
 
             (int origin, BitBoard _) => MakeMoveAttacks.PawnAttacks[(int)Side.Black, origin],
             (int origin, BitBoard _) => MakeMoveAttacks.KnightAttacks[origin],
             (int origin, BitBoard occupancy) => MakeMoveAttacks.BishopAttacks(origin, occupancy),
             (int origin, BitBoard occupancy) => MakeMoveAttacks.RookAttacks(origin, occupancy),
-            // TODO try to improve performance by re-using bishop and rook attacks
             (int origin, BitBoard occupancy) => MakeMoveAttacks.QueenAttacks(origin, occupancy),
             (int origin, BitBoard _) => MakeMoveAttacks.KingAttacks[origin],
         };
@@ -1404,4 +1404,6 @@ private static bool IsSquareAttackedByQueens(int offset, BitBoard bishopAttacks,
     }
 
     #endregion
-}
+}
+
+#pragma warning restore S101, S1854 // Types should be named in PascalCase

src/Lynx.Benchmark/MakeUnmakeMove_integration.cs

@@ -142,6 +142,7 @@
  *  |   MakeUnmakeMove_PassRef | (rnbq(...)1, 4) [61] |  27.016 ms |  0.5351 ms |  0.8940 ms |  26.693 ms |  0.97 |    0.05 |   375.0000 |       - |    9.54 MB |        0.22 |
  */
 
+#pragma warning disable S101, S1854 // Types should be named in PascalCase
 using BenchmarkDotNet.Attributes;
 using Lynx.Model;
 using NLog;
@@ -156,7 +157,7 @@ public class MakeUnmakeMove_integration : BaseBenchmark
             ("r4rk1/1pp1qppp/p1np1n2/2b1p1B1/2B1P1b1/P1NP1N2/1PP1QPPP/R4RK1 w - - 0 10", 4),
             ("3K4/8/8/8/8/8/4p3/2k2R2 b - - 0 1", 6),
             ("2K2r2/4P3/8/8/8/8/8/3k4 w - - 0 1", 6),
-            ("8/p7/8/1P6/K1k3p1/6P1/7P/8 w - -", 6),
+            ("8/p7/8/1P6/K1k3p1/6P1/7P/8 w - -", 6)
         };
 
     [Benchmark(Baseline = true)]
@@ -1178,7 +1179,7 @@ public void UnMakeNullMove(MakeMoveGameState gameState)
         /// </summary>
         /// <returns></returns>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        internal bool IsValid()
+        internal readonly bool IsValid()
         {
             var kingBitBoard = PieceBitBoards[(int)Piece.K + Utils.PieceOffset(Side)];
             var kingSquare = kingBitBoard == default ? -1 : kingBitBoard.GetLS1BIndex();
@@ -1197,7 +1198,7 @@ internal bool IsValid()
         /// </summary>
         /// <returns></returns>
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public bool WasProduceByAValidMove()
+        public readonly bool WasProduceByAValidMove()
         {
             var oppositeKingBitBoard = PieceBitBoards[(int)Piece.K + Utils.PieceOffset((Side)Utils.OppositeSide(Side))];
             var oppositeKingSquare = oppositeKingBitBoard == default ? -1 : oppositeKingBitBoard.GetLS1BIndex();
@@ -1206,7 +1207,7 @@ public bool WasProduceByAValidMove()
         }
 
         [MethodImpl(MethodImplOptions.AggressiveInlining)]
-        public IEnumerable<Move> AllPossibleMoves(Move[]? movePool = null) => MakeMoveMoveGenerator.GenerateAllMoves(this, movePool);
+        public readonly IEnumerable<Move> AllPossibleMoves(Move[]? movePool = null) => MakeMoveMoveGenerator.GenerateAllMoves(this, movePool);
     }
 
     public readonly struct MakeMoveGameState
@@ -1245,19 +1246,17 @@ public MakeMoveGameState_PassOut(int capturedPiece, int castle, BoardSquare enpa
         }
     }
 
-
     public struct MakeMoveGameState_PassRef
     {
+#pragma warning disable S1104 // Fields should not have public accessibility
         public int CapturedPiece;
 
         public int Castle;
 
         public BoardSquare EnPassant;
-
-        // TODO: save full Zobrist key?
+#pragma warning restore S1104 // Fields should not have public accessibility
     }
 
-
     #region ;(
 
     public static class MakeMoveZobristTable
@@ -1403,15 +1402,13 @@ public static class MakeMoveMoveGenerator
             (int origin, BitBoard _) => MakeMoveAttacks.KnightAttacks[origin],
             (int origin, BitBoard occupancy) => MakeMoveAttacks.BishopAttacks(origin, occupancy),
             (int origin, BitBoard occupancy) => MakeMoveAttacks.RookAttacks(origin, occupancy),
-            // TODO try to improve performance by re-using bishop and rook attacks
             (int origin, BitBoard occupancy) => MakeMoveAttacks.QueenAttacks(origin, occupancy),
             (int origin, BitBoard _) => MakeMoveAttacks.KingAttacks[origin],
 
             (int origin, BitBoard _) => MakeMoveAttacks.PawnAttacks[(int)Side.Black, origin],
             (int origin, BitBoard _) => MakeMoveAttacks.KnightAttacks[origin],
             (int origin, BitBoard occupancy) => MakeMoveAttacks.BishopAttacks(origin, occupancy),
             (int origin, BitBoard occupancy) => MakeMoveAttacks.RookAttacks(origin, occupancy),
-            // TODO try to improve performance by re-using bishop and rook attacks
             (int origin, BitBoard occupancy) => MakeMoveAttacks.QueenAttacks(origin, occupancy),
             (int origin, BitBoard _) => MakeMoveAttacks.KingAttacks[origin],
         };
@@ -1817,4 +1814,6 @@ private static bool IsSquareAttackedByQueens(int offset, BitBoard bishopAttacks,
     }
 
     #endregion
-}
+}
+
+#pragma warning restore S101, S1854 // Types should be named in PascalCase

src/Lynx.Cli/Program.cs

@@ -68,6 +68,7 @@
     engineChannel.Writer.TryComplete();
     uciChannel.Writer.TryComplete();
     //source.Cancel();
+    NLog.LogManager.Shutdown(); // Flush and close down internal threads and timers
 }
 
 Thread.Sleep(2_000);

src/Lynx.Cli/appsettings.Development.json

@@ -6,6 +6,8 @@
     "UseOnlineTablebaseInSearch": false
   },
   "NLog": {
+    "internalLogLevel": "Warn",
+    "throwExceptions": true,
     "targets": {
       "console": {
         "type": "ColoredConsole",

src/Lynx.Cli/appsettings.json

@@ -58,15 +58,16 @@
 
   // Logging settings
   "NLog": {
-    "autoreload": true,
+    "autoreload": false,
     "internalLogLevel": "Error",
     "internalLogFile": "${basedir}/logs/internal-nlog.txt",
-    "throwExceptions": true,
+    "throwExceptions": false,
     "variables": {
       "logDirectory": "${basedir}/logs",
       "archiveLogDirectory": "${basedir}/logs/archives"
     },
     "targets": {
+      "async": true,
       "errors": {
         "type": "File",
         "layout": "${longdate}|${event-properties:item=EventId_Id:whenEmpty=0}|${processid}|${uppercase:${level}}|${logger}|${message} ${exception:format=tostring}",
@@ -186,4 +187,4 @@
       }
     }
   }
-}
+}

src/Lynx/Constants.cs

@@ -354,7 +354,7 @@ public static class Constants
     ///  Black kingside Rook moved      1111 & 1011  =  1011    11
     ///  Black queenside Rook moved     1111 & 0111  =  0111    7
     /// </summary>
-    public static readonly int[] CastlingRightsUpdateConstants = new int[64]
+    public static readonly byte[] CastlingRightsUpdateConstants = new byte[64]
     {
             7, 15, 15, 15,  3, 15, 15, 11,
             15, 15, 15, 15, 15, 15, 15, 15,

src/Lynx/Engine.cs

@@ -154,7 +154,6 @@ private SearchResult SearchBestMove(int minDepth, int? maxDepth, int? decisionTi
         // Local copy of positionHashHistory and HalfMovesWithoutCaptureOrPawnMove so that it doesn't interfere with regular search
         var currentHalfMovesWithoutCaptureOrPawnMove = Game.HalfMovesWithoutCaptureOrPawnMove;
 
-
         var tasks = new Task<SearchResult?>[] {
             ProbeOnlineTablebase(Game.CurrentPosition, new(Game.PositionHashHistory), currentHalfMovesWithoutCaptureOrPawnMove),  // Other copies of positionHashHistory and HalfMovesWithoutCaptureOrPawnMove (same reason)
             IDDFS(minDepth, maxDepth, decisionTime),

src/Lynx/FENParser.cs

@@ -13,7 +13,7 @@ public static partial class FENParser
 
     private static readonly Logger _logger = LogManager.GetCurrentClassLogger();
 
-    public static (bool Success, BitBoard[] PieceBitBoards, BitBoard[] OccupancyBitBoards, Side Side, int Castle, BoardSquare EnPassant,
+    public static (bool Success, BitBoard[] PieceBitBoards, BitBoard[] OccupancyBitBoards, Side Side, byte Castle, BoardSquare EnPassant,
         int HalfMoveClock, int FullMoveCounter) ParseFEN(string fen)
     {
         fen = fen.Trim();
@@ -27,7 +27,7 @@ public static partial class FENParser
 
         bool success;
         Side side = Side.Both;
-        int castle = 0;
+        byte castle = 0;
         int halfMoveClock = 0, fullMoveCounter = 1;
         BoardSquare enPassant = BoardSquare.noSquare;
 
@@ -140,18 +140,18 @@ private static Side ParseSide(string sideString)
 #pragma warning restore S3358 // Ternary operators should not be nested
     }
 
-    private static int ParseCastlingRights(string castleString)
+    private static byte ParseCastlingRights(string castleString)
     {
-        int castle = 0;
+        byte castle = 0;
 
         foreach (var ch in castleString)
         {
             castle |= ch switch
             {
-                'K' => (int)CastlingRights.WK,
-                'Q' => (int)CastlingRights.WQ,
-                'k' => (int)CastlingRights.BK,
-                'q' => (int)CastlingRights.BQ,
+                'K' => (byte)CastlingRights.WK,
+                'Q' => (byte)CastlingRights.WQ,
+                'k' => (byte)CastlingRights.BK,
+                'q' => (byte)CastlingRights.BQ,
                 '-' => castle,
                 _ => throw new($"Unrecognized castling char: {ch}")
             };

src/Lynx/LinxDriver.cs

@@ -276,7 +276,7 @@ private void HandleDivide(string rawCommand)
 
         if (items.Length >= 2 && int.TryParse(items[1], out int depth) && depth >= 1)
         {
-            Perft.Results(_engine.Game.CurrentPosition, depth);
+            Perft.Divide(_engine.Game.CurrentPosition, depth);
         }
     }
 

src/Lynx/Model/BitBoard.cs

@@ -1,5 +1,6 @@
 using System.Numerics;
 using System.Runtime.CompilerServices;
+using System.Runtime.Intrinsics.X86;
 
 #pragma warning disable S4136
 
@@ -121,6 +122,11 @@ public static int GetLS1BIndex(this BitBoard board)
     {
         Utils.Assert(board != default);
 
+        if (Bmi1.X64.IsSupported)
+        {
+            return (int)Bmi1.X64.TrailingZeroCount(board);
+        }
+
         return BitOperations.TrailingZeroCount(board);
     }
 
@@ -149,6 +155,11 @@ public static void ResetLS1B(this ref BitBoard board)
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static int CountBits(this BitBoard board)
     {
+        if (Popcnt.X64.IsSupported)
+        {
+            return (int)Popcnt.X64.PopCount(board);
+        }
+
         return BitOperations.PopCount(board);
     }
 

src/Lynx/Model/BoardSquare.cs

@@ -13,7 +13,7 @@
 ///         SW       S      SE
 ///
 /// </summary>
-public enum BoardSquare
+public enum BoardSquare : sbyte
 {
     a8, b8, c8, d8, e8, f8, g8, h8,
     a7, b7, c7, d7, e7, f7, g7, h7,

src/Lynx/Model/CastlingRights.cs

@@ -10,7 +10,7 @@
 /// * 1111      Both sides can castle both directions
 /// * 1001      Black king => only O-O-O; White king => only O-O
 /// </summary>
-public enum CastlingRights
+public enum CastlingRights : byte
 {
     WK = 1, WQ = 2, BK = 4, BQ = 8
 }

src/Lynx/Model/GameState.cs

@@ -1,17 +1,17 @@
 namespace Lynx.Model;
 public readonly struct GameState
 {
-    public readonly int CapturedPiece;
+    public readonly sbyte CapturedPiece;
 
-    public readonly int Castle;
+    public readonly byte Castle;
 
     public readonly BoardSquare EnPassant;
 
     public readonly long ZobristKey;
 
     // TODO: save full Zobrist key?
 
-    public GameState(int capturedPiece, int castle, BoardSquare enpassant, long zobristKey)
+    public GameState(sbyte capturedPiece, byte castle, BoardSquare enpassant, long zobristKey)
     {
         CapturedPiece = capturedPiece;
         Castle = castle;

src/Lynx/Model/Piece.cs

@@ -1,6 +1,6 @@
 namespace Lynx.Model;
 
-public enum Piece
+public enum Piece : sbyte
 {
     Unknown = -1,
     P, N, B, R, Q, K,   // White