From 24c57793e1917b2110d1e3ce8edc634f43eadc67 Mon Sep 17 00:00:00 2001
From: MinetaS <skdty87@gmail.com>
Date: Wed, 30 Oct 2024 21:30:21 +0900
Subject: [PATCH] Remove moveCountPruning in search.cpp

The definition of moveCountPruning may cause confusion by implying that
the variable is unconstrained. However, once it is set to true, it
should not be reset to false, otherwise it would break the internal
logic of MovePicker.

Several patches have overlooked this constraint. For example:
https://tests.stockfishchess.org/tests/view/671e7c0486d5ee47d953d226
https://tests.stockfishchess.org/tests/view/66a1de7b4ff211be9d4eccea

The implementation approach was suggested by Disservin.

Passed non-regression STC:
LLR: 3.02 (-2.94,2.94) <-1.75,0.25>
Total: 180672 W: 47072 L: 47006 D: 86594
Ptnml(0-2): 536, 19482, 50247, 19522, 549
https://tests.stockfishchess.org/tests/view/6720df6f86d5ee47d953d542

closes https://github.com/official-stockfish/Stockfish/pull/5661

No functional change
---
 src/movepick.cpp | 4 +++-
 src/movepick.h   | 4 +++-
 src/search.cpp   | 8 ++++----
 3 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/src/movepick.cpp b/src/movepick.cpp
index 0649518938a..2a1fb837348 100644
--- a/src/movepick.cpp
+++ b/src/movepick.cpp
@@ -216,7 +216,7 @@ Move MovePicker::select(Pred filter) {
 // This is the most important method of the MovePicker class. We emit one
 // new pseudo-legal move on every call until there are no more moves left,
 // picking the move with the highest score from a list of generated moves.
-Move MovePicker::next_move(bool skipQuiets) {
+Move MovePicker::next_move() {
 
     auto quiet_threshold = [](Depth d) { return -3560 * d; };
 
@@ -322,4 +322,6 @@ Move MovePicker::next_move(bool skipQuiets) {
     return Move::none();  // Silence warning
 }
 
+void MovePicker::skip_quiet_moves() { skipQuiets = true; }
+
 }  // namespace Stockfish
diff --git a/src/movepick.h b/src/movepick.h
index dff09f79c3e..f8f84d02474 100644
--- a/src/movepick.h
+++ b/src/movepick.h
@@ -212,7 +212,8 @@ class MovePicker {
                const PawnHistory*,
                int);
     MovePicker(const Position&, Move, int, const CapturePieceToHistory*);
-    Move next_move(bool skipQuiets = false);
+    Move next_move();
+    void skip_quiet_moves();
 
    private:
     template<PickType T, typename Pred>
@@ -234,6 +235,7 @@ class MovePicker {
     int                          threshold;
     Depth                        depth;
     int                          ply;
+    bool                         skipQuiets = false;
     ExtMove                      moves[MAX_MOVES];
 };
 
diff --git a/src/search.cpp b/src/search.cpp
index c7a8c28b474..4864057c1b1 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -942,12 +942,11 @@ Value Search::Worker::search(
 
     value = bestValue;
 
-    int  moveCount        = 0;
-    bool moveCountPruning = false;
+    int moveCount = 0;
 
     // Step 13. Loop through all pseudo-legal moves until no moves remain
     // or a beta cutoff occurs.
-    while ((move = mp.next_move(moveCountPruning)) != Move::none())
+    while ((move = mp.next_move()) != Move::none())
     {
         assert(move.is_ok());
 
@@ -993,7 +992,8 @@ Value Search::Worker::search(
         if (!rootNode && pos.non_pawn_material(us) && bestValue > VALUE_TB_LOSS_IN_MAX_PLY)
         {
             // Skip quiet moves if movecount exceeds our FutilityMoveCount threshold (~8 Elo)
-            moveCountPruning = moveCount >= futility_move_count(improving, depth);
+            if (moveCount >= futility_move_count(improving, depth))
+                mp.skip_quiet_moves();
 
             // Reduced depth of the next LMR search
             int lmrDepth = newDepth - r;