Added threefold repetition detection, released v1.1.7

Author: Timmoth

.github/workflows/release-pipeline.yaml

@@ -25,7 +25,7 @@ jobs:
         working-directory: Sapling
         id: get_version
         run: |
-          VERSION=1.1.6
+          VERSION=1.1.7
           echo "Application version: $VERSION"
           echo "::set-output name=version::$VERSION"
 

Sapling.Engine/RepetitionDetector.cs

@@ -76,6 +76,34 @@ ulong AttackMask(int idx, int piece)
         }
     }
 
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public static bool IsThreefoldRepetition(ushort turnCount, ushort halfMoveClock, ulong* hashHistory)
+    {
+        if (halfMoveClock < 3)
+            return false;
+
+        var currHash = hashHistory + turnCount - 1;
+
+        var initialHash = *(currHash);
+
+        var count = 1;
+        for (var i = 2; i < halfMoveClock; i+=2)
+        {
+            currHash -= 2;
+            if (*(currHash) != initialHash)
+            {
+                continue;
+            }
+
+            if (++count >= 3)
+            {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     public static bool HasRepetition(this ref BoardStateData pos, ulong* hashHistory, int depthFromRoot)
     {

Sapling.Engine/Search/NegaMaxSearch.cs

@@ -54,7 +54,9 @@ public unsafe int
                 return alpha;
             }
 
-            if (currentBoardState->HalfMoveClock >= 100 || currentBoardState->InsufficientMatingMaterial())
+            if (currentBoardState->HalfMoveClock >= 100 || 
+                currentBoardState->InsufficientMatingMaterial() || 
+                RepetitionDetector.IsThreefoldRepetition(currentBoardState->TurnCount, currentBoardState->HalfMoveClock, HashHistory))
             {
                 // Detect draw by Fifty move counter or repetition
                 return 0;
@@ -248,6 +250,7 @@ public unsafe int
                 counterMove);
         }
 
+        var nextHashHistoryEntry = HashHistory + currentBoardState->TurnCount;
         var probCutSortedUpTo = 0;
 
         // Probcut
@@ -316,6 +319,7 @@ public unsafe int
                 {
                     newBoardState->FinishApplyBlack(ref *newAccumulatorState, m, currentBoardState->EnPassantFile, currentBoardState->CastleRights);
                 }
+                *nextHashHistoryEntry = newBoardState->Hash;
 
                 NodesVisited--;
                 var score = -QuiescenceSearch(newBoardState, newAccumulatorState, depthFromRoot + 1, -probBeta, -probBeta + 1);
@@ -344,7 +348,6 @@ public unsafe int
 
         uint bestMove = default;
         var evaluationBound = TranspositionTableFlag.Alpha;
-        var nextHashHistoryEntry = HashHistory + currentBoardState->TurnCount;
 
         var bestScore = int.MinValue;
         // Evaluate each move

Sapling.Engine/Search/QuiescenceSearch.cs

@@ -1,5 +1,4 @@
-using System.IO;
-using System.Runtime.CompilerServices;
+using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using System.Runtime.Intrinsics.X86;
 using Sapling.Engine.MoveGen;
@@ -27,7 +26,9 @@ public unsafe int QuiescenceSearch(BoardStateData* boardState, AccumulatorState*
             return Evaluate(boardState, accumulatorState, depthFromRoot);
         }
 
-        if (boardState->InsufficientMatingMaterial())
+        if (boardState->HalfMoveClock >= 100 ||
+            boardState->InsufficientMatingMaterial() ||
+            RepetitionDetector.IsThreefoldRepetition(boardState->TurnCount, boardState->HalfMoveClock, HashHistory))
         {
             // Detect draw by Fifty move counter or repetition
             return 0;

Sapling/Sapling.csproj

@@ -7,9 +7,9 @@
     <Nullable>enable</Nullable>
     <ApplicationIcon>logo.ico</ApplicationIcon>
     <Title>Sapling</Title>
-	  <AssemblyVersion>1.1.6.0</AssemblyVersion>
-	  <FileVersion>1.1.6.0</FileVersion>
-	  <Version>1.1.6.0</Version>
+	  <AssemblyVersion>1.1.7.0</AssemblyVersion>
+	  <FileVersion>1.1.7.0</FileVersion>
+	  <Version>1.1.7.0</Version>
 	  <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   </PropertyGroup>