From 4481947470ca555e6cbdb7df551c80532eca0c9c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Eduardo=20C=C3=A1ceres?=
 <eduardo.caceresdelacalle@gmail.com>
Date: Sun, 5 Jan 2025 18:21:35 +0100
Subject: [PATCH] Add history component to RFP

---
 src/Lynx/Configuration.cs  | 3 +++
 src/Lynx/Search/NegaMax.cs | 4 +++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/Lynx/Configuration.cs b/src/Lynx/Configuration.cs
index a4df158a8..370c8d8c0 100644
--- a/src/Lynx/Configuration.cs
+++ b/src/Lynx/Configuration.cs
@@ -186,6 +186,9 @@ public int Threads
     [SPSA<int>(1, 300, 15)]
     public int RFP_DepthScalingFactor { get; set; } = 52;
 
+    [SPSA<int>(200, 600, 20)]
+    public int RFP_HistoryDivisor { get; set; } = 400;
+
     [SPSA<int>(1, 10, 0.5)]
     public int Razoring_MaxDepth { get; set; } = 2;
 
diff --git a/src/Lynx/Search/NegaMax.cs b/src/Lynx/Search/NegaMax.cs
index 028abb81d..41b143e92 100644
--- a/src/Lynx/Search/NegaMax.cs
+++ b/src/Lynx/Search/NegaMax.cs
@@ -148,8 +148,10 @@ private int NegaMax(int depth, int ply, int alpha, int beta, bool cutnode, Cance
                     var improvingFactor = improvingRate * (0.75 * depth);
 
                     var rfpThreshold = rfpMargin + improvingFactor;
+                    var previousMove = Game.ReadMoveFromStack(ply - 1);
+                    var previousMoveHistory = _quietHistory[previousMove.Piece()][previousMove.TargetSquare()];
 
-                    if (staticEval - rfpThreshold >= beta)
+                    if (staticEval - rfpThreshold >= beta + previousMoveHistory / Configuration.EngineSettings.RFP_HistoryDivisor)
                     {
 #pragma warning disable S3949 // Calculations should not overflow - value is being set at the beginning of the else if (!pvNode)
                         return (staticEval + beta) / 2;