Add 'modern' razoring implementation

lynx-chess · May 16, 2024 · eb6b44f · eb6b44f
1 parent 19b2ee9
commit eb6b44f
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Showing 4 changed files with 52 additions and 1 deletion.
diff --git a/src/Lynx.Cli/appsettings.json b/src/Lynx.Cli/appsettings.json
@@ -57,6 +57,10 @@
     "FP_DepthScalingFactor": 60,
     "FP_Margin": 250,
 
+    "Razoring2_MaxDepth": 4,
+    "Razoring2_AlphaMargin": 2000,
+    "Razoring2_DepthScalingFactor": 250,
+
     // Evaluation
     "IsolatedPawnPenalty": {
       "MG": -21,

diff --git a/src/Lynx/Configuration.cs b/src/Lynx/Configuration.cs
@@ -155,7 +155,10 @@ public sealed class EngineSettings
     [SPSAAttribute<int>(1, 20, 1)]
     public int AspirationWindow_MinDepth { get; set; } = 7;
 
-    [SPSAAttribute<int>(1, 20, 1)]
+    /// <summary>
+    /// Min 2 due to existing logic that assumes RFP_MaxDepth >= Razoring_MaxDepth
+    /// </summary>
+    [SPSAAttribute<int>(2, 20, 1)]
     public int RFP_MaxDepth { get; set; } = 6;
 
     [SPSAAttribute<int>(1, 300, 10)]
@@ -201,6 +204,15 @@ public sealed class EngineSettings
     [SPSAAttribute<int>(0, 500, 25)]
     public int FP_Margin { get; set; } = 250;
 
+    [SPSAAttribute<int>(1, 10, 1)]
+    public int Razoring2_MaxDepth { get; set; } = 4;
+
+    [SPSAAttribute<int>(1000, 5000, 500)]
+    public int Razoring2_AlphaMargin { get; set; } = 2000;
+
+    [SPSAAttribute<int>(50, 500, 50)]
+    public int Razoring2_DepthScalingFactor { get; set; } = 250;
+
     #region Evaluation
 
     public TaperedEvaluationTerm IsolatedPawnPenalty { get; set; } = new(-21, -17);

diff --git a/src/Lynx/Search/NegaMax.cs b/src/Lynx/Search/NegaMax.cs
@@ -97,6 +97,17 @@ private int NegaMax(int depth, int ply, int alpha, int beta, bool parentWasNullM
                 staticEval = ttScore;
             }
 
+            // Razoring implementation, according to modern standards. Based on Ciekce + JW
+            if (depth <= Configuration.EngineSettings.Razoring2_MaxDepth
+                && Math.Abs(alpha) < 2000
+                && staticEval + (Configuration.EngineSettings.Razoring2_DepthScalingFactor * depth) <= alpha)
+            {
+                var score = QuiescenceSearch(ply, alpha, alpha + 1);
+
+                if (score <= alpha)
+                    return score;
+            }
+
             if (depth <= Configuration.EngineSettings.RFP_MaxDepth)
             {
                 // 🔍 Reverse Futility Pruning (RFP) - https://www.chessprogramming.org/Reverse_Futility_Pruning

diff --git a/src/Lynx/UCIHandler.cs b/src/Lynx/UCIHandler.cs
@@ -456,6 +456,30 @@ private void HandleSetOption(ReadOnlySpan<char> command)
                     }
                     break;
                 }
+            case "razoring2_maxdepth":
+                {
+                    if (length > 4 && int.TryParse(command[commandItems[4]], out var value))
+                    {
+                        Configuration.EngineSettings.Razoring2_MaxDepth = value;
+                    }
+                    break;
+                }
+            case "razoring2_alphamargin":
+                {
+                    if (length > 4 && int.TryParse(command[commandItems[4]], out var value))
+                    {
+                        Configuration.EngineSettings.Razoring2_AlphaMargin = value;
+                    }
+                    break;
+                }
+            case "razoring2_depthscalingfactor":
+                {
+                    if (length > 4 && int.TryParse(command[commandItems[4]], out var value))
+                    {
+                        Configuration.EngineSettings.Razoring2_DepthScalingFactor = value;
+                    }
+                    break;
+                }
 
             #endregion