From 0dcfe096d6223ea8c5663cf72f714280a38d8506 Mon Sep 17 00:00:00 2001
From: Nonlinear2 <131959792+Nonlinear2@users.noreply.github.com>
Date: Mon, 21 Apr 2025 15:13:30 +0200
Subject: [PATCH] Increase full depth search reduction when cutNode

In addition to the core patch, improve the use of `isTTMove`:

- this name was used to mean both `bestMove == ttData.move` and `move == ttData.move`, so i replaced the argument `isTTMove` of `update_all_stats` with `TTMove` directly.

- `ttData.move == move` was  still used in some places instead of `ss->isTTMove`. I replaced these to be more consistent.

Passed STC:
https://tests.stockfishchess.org/tests/view/68057b8f98cd372e3aea3472
LLR: 2.93 (-2.94,2.94) <0.00,2.00>
Total: 38400 W: 10048 L: 9734 D: 18618
Ptnml(0-2): 102, 4360, 9956, 4686, 96

Passed LTC:
https://tests.stockfishchess.org/tests/view/68057f7c98cd372e3aea3842
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 312666 W: 79494 L: 78616 D: 154556
Ptnml(0-2): 144, 33809, 87563, 34659, 158

closes https://github.com/official-stockfish/Stockfish/pull/6007

Bench: 1623376
---
 src/search.cpp | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/src/search.cpp b/src/search.cpp
index b8a4b32a6..85e4d0077 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -164,7 +164,7 @@ void update_all_stats(const Position&      pos,
                       ValueList<Move, 32>& quietsSearched,
                       ValueList<Move, 32>& capturesSearched,
                       Depth                depth,
-                      bool                 isTTMove,
+                      Move                 TTMove,
                       int                  moveCount);
 
 }  // namespace
@@ -1098,8 +1098,9 @@ moves_loop:  // When in check, search starts here
 
                 lmrDepth += history / 3593;
 
-                Value futilityValue = ss->staticEval + (bestMove ? 48 : 146) + 116 * lmrDepth
-                                    + 103 * (bestValue < ss->staticEval - 128 && ss->staticEval > alpha - 50);
+                Value futilityValue =
+                  ss->staticEval + (bestMove ? 48 : 146) + 116 * lmrDepth
+                  + 103 * (bestValue < ss->staticEval - 128 && ss->staticEval > alpha - 50);
 
                 // Futility pruning: parent node
                 // (*Scaler): Generally, more frequent futility pruning
@@ -1231,7 +1232,7 @@ moves_loop:  // When in check, search starts here
             r += 1042 + allNode * 864;
 
         // For first picked move (ttMove) reduce reduction
-        else if (move == ttData.move)
+        else if (ss->isTTMove)
             r -= 1937;
 
         if (capture)
@@ -1302,6 +1303,9 @@ moves_loop:  // When in check, search starts here
 
             r -= ttMoveHistory / 8;
 
+            if (cutNode)
+                r += 520;
+
             // Note that if expected reduction is high, we reduce search depth here
             value = -search<NonPV>(pos, ss + 1, -(alpha + 1), -alpha,
                                    newDepth - (r > 3495) - (r > 5510 && newDepth > 2), !cutNode);
@@ -1315,7 +1319,7 @@ moves_loop:  // When in check, search starts here
             (ss + 1)->pv[0] = Move::none();
 
             // Extend move from transposition table if we are about to dive into qsearch.
-            if (move == ttData.move && thisThread->rootDepth > 8)
+            if (ss->isTTMove && thisThread->rootDepth > 8)
                 newDepth = std::max(newDepth, 1);
 
             value = -search<PV>(pos, ss + 1, -beta, -alpha, newDepth, false);
@@ -1450,10 +1454,10 @@ moves_loop:  // When in check, search starts here
     else if (bestMove)
     {
         update_all_stats(pos, ss, *this, bestMove, prevSq, quietsSearched, capturesSearched, depth,
-                         bestMove == ttData.move, moveCount);
+                         ttData.move, moveCount);
         if (!PvNode)
         {
-            int bonus = (ttData.move == move) ? 800 : -870;
+            int bonus = ss->isTTMove ? 800 : -870;
             ttMoveHistory << bonus;
         }
     }
@@ -1877,14 +1881,14 @@ void update_all_stats(const Position&      pos,
                       ValueList<Move, 32>& quietsSearched,
                       ValueList<Move, 32>& capturesSearched,
                       Depth                depth,
-                      bool                 isTTMove,
+                      Move                 TTMove,
                       int                  moveCount) {
 
     CapturePieceToHistory& captureHistory = workerThread.captureHistory;
     Piece                  moved_piece    = pos.moved_piece(bestMove);
     PieceType              captured;
 
-    int bonus = std::min(141 * depth - 89, 1613) + 311 * isTTMove;
+    int bonus = std::min(141 * depth - 89, 1613) + 311 * (bestMove == TTMove);
     int malus = std::min(695 * depth - 215, 2808) - 31 * (moveCount - 1);
 
     if (!pos.capture_stage(bestMove))