Merge branch 'refactor/tm-outside-of-engine' into refactor/tt-outside…

…-of-engine-1-static
lynx-chess · Nov 11, 2024 · c362b08 · c362b08
2 parents 6c3e819 + 55e0eee
commit c362b08
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Showing 4 changed files with 46 additions and 9 deletions.
diff --git a/src/Lynx/Configuration.cs b/src/Lynx/Configuration.cs
@@ -142,6 +142,12 @@ public int TranspositionTableSize
     [SPSA<int>(1, 10, 0.5)]
     public int NMP_DepthDivisor { get; set; } = 3;
 
+    [SPSA<int>(150, 350, 10)]
+    public int NMP_StaticEvalBetaDivisor { get; set; } = 100;
+
+    [SPSA<int>(1, 10, 0.5)]
+    public int NMP_StaticEvalBetaMaxReduction { get; set; } = 3;
+
     [SPSA<int>(5, 30, 1)]
     public int AspirationWindow_Base { get; set; } = 13;
 

diff --git a/src/Lynx/Search/NegaMax.cs b/src/Lynx/Search/NegaMax.cs
@@ -1,6 +1,7 @@
 using Lynx.Model;
 using System.Diagnostics;
 using System.Runtime.CompilerServices;
+using System.Security.Authentication;
 
 using static Lynx.Model.TranspositionTable;
 
@@ -78,6 +79,9 @@ private int NegaMax(int depth, int ply, int alpha, int beta, bool parentWasNullM
         // - Prune less aggressively when evaluation is low low: uncertainty on how bad the position really is
         bool improving = false;
 
+        // From Potential
+        double improvingRate = 0;
+
         bool isInCheck = position.IsInCheck();
         int staticEval = int.MaxValue;
         int phase = int.MaxValue;
@@ -115,7 +119,9 @@ private int NegaMax(int depth, int ply, int alpha, int beta, bool parentWasNullM
 
             if (ply >= 2)
             {
-                improving = staticEval > Game.ReadStaticEvalFromStack(ply - 2);
+                var evalDiff = staticEval - Game.ReadStaticEvalFromStack(ply - 2);
+                improving = evalDiff >= 0;
+                improvingRate = evalDiff / 50.0;
             }
 
             // From smol.cs
@@ -133,7 +139,13 @@ private int NegaMax(int depth, int ply, int alpha, int beta, bool parentWasNullM
             {
                 // 🔍 Reverse Futility Pruning (RFP) - https://www.chessprogramming.org/Reverse_Futility_Pruning
                 // Return formula by Ciekce, instead of just returning static eval
-                if (staticEval - (Configuration.EngineSettings.RFP_DepthScalingFactor * (depth - (improving ? 1 : 0))) >= beta)
+                // Improving impl. based on Potential's
+                var rfpMargin = improving ? 80 * (depth - 1) : 100 * depth;
+                var improvingFactor = improvingRate * (0.75 * depth);
+
+                var rfpThreshold = rfpMargin + improvingFactor;
+
+                if (staticEval - rfpThreshold >= beta)
                 {
 #pragma warning disable S3949 // Calculations should not overflow - value is being set at the beginning of the else if (!pvNode)
                     return (staticEval + beta) / 2;
@@ -172,14 +184,20 @@ private int NegaMax(int depth, int ply, int alpha, int beta, bool parentWasNullM
                 }
             }
 
+            var staticEvalBetaDiff = staticEval - beta;
+
             // 🔍 Null Move Pruning (NMP) - our position is so good that we can potentially afford giving our opponent a double move and still remain ahead of beta
             if (depth >= Configuration.EngineSettings.NMP_MinDepth
-                && staticEval >= beta
+                && staticEvalBetaDiff >= 0
                 && !parentWasNullMove
                 && phase > 2   // Zugzwang risk reduction: pieces other than pawn presents
                 && (ttElementType != NodeType.Alpha || ttScore >= beta))   // TT suggests NMP will fail: entry must not be a fail-low entry with a score below beta - Stormphrax and Ethereal
             {
-                var nmpReduction = Configuration.EngineSettings.NMP_BaseDepthReduction + ((depth + Configuration.EngineSettings.NMP_DepthIncrement) / Configuration.EngineSettings.NMP_DepthDivisor);   // Clarity
+                var nmpReduction = Configuration.EngineSettings.NMP_BaseDepthReduction
+                    + ((depth + Configuration.EngineSettings.NMP_DepthIncrement) / Configuration.EngineSettings.NMP_DepthDivisor)   // Clarity
+                    + Math.Min(
+                        Configuration.EngineSettings.NMP_StaticEvalBetaMaxReduction,
+                        staticEvalBetaDiff / Configuration.EngineSettings.NMP_StaticEvalBetaDivisor);
 
                 // TODO more advanced adaptative reduction, similar to what Ethereal and Stormphrax are doing
                 //var nmpReduction = Math.Min(

diff --git a/src/Lynx/UCIHandler.cs b/src/Lynx/UCIHandler.cs
@@ -336,6 +336,22 @@ private void HandleSetOption(ReadOnlySpan<char> command)
                     }
                     break;
                 }
+            case "nmp_staticevalbetadivisor":
+                {
+                    if (length > 4 && int.TryParse(command[commandItems[4]], out var value))
+                    {
+                        Configuration.EngineSettings.NMP_StaticEvalBetaDivisor = value;
+                    }
+                    break;
+                }
+            case "nmp_staticevalbetamaxreduction":
+                {
+                    if (length > 4 && int.TryParse(command[commandItems[4]], out var value))
+                    {
+                        Configuration.EngineSettings.NMP_StaticEvalBetaMaxReduction = value;
+                    }
+                    break;
+                }
 
             //case "aspirationwindow_delta":
             //    {

diff --git a/tests/Lynx.Test/BestMove/RegressionTest.cs b/tests/Lynx.Test/BestMove/RegressionTest.cs
@@ -67,15 +67,12 @@ public void KeepNonGoodQuiescenceMoves(int depth)
 
         switch (depth)
         {
-            case 5:
+            case 5 when bestResult.Moves.Length >= 5:
                 Assert.AreNotEqual("f6e4", bestResult.Moves[4].UCIString());
                 break;
-            case 6:
+            case 6 when bestResult.Moves.Length >= 6:
                 Assert.AreNotEqual("f3e5", bestResult.Moves[5].UCIString());
                 break;
-            default:
-                Assert.True(false);
-                break;
         }
     }