From 009632c465ef8204884b01c0307f7e15106fd94e Mon Sep 17 00:00:00 2001
From: mstembera <m_stembera@yahoo.com>
Date: Fri, 16 May 2025 13:04:10 -0700
Subject: [PATCH] Simplify handling of good/bad quiets

Simplify the handling of good/bad quiets and make it more similar to the way we
handle good/bad captures. The good quiet limit was adjusted from -7998 to
-14000 to keep the ratio of good/bad quiets about the same as master.  This
also fixes a "bug" that previously returned some bad quiets during the
GOOD_QUIET stage when some qood quiets weren't sorted at low depths.

STC https://tests.stockfishchess.org/tests/view/6827a68c6ec7634154f9992b
LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 75936 W: 19722 L: 19547 D: 36667
Ptnml(0-2): 186, 8937, 19589, 9028, 228

LTC https://tests.stockfishchess.org/tests/view/6828f8096ec7634154f99b82
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 104112 W: 26773 L: 26638 D: 50701
Ptnml(0-2): 51, 11363, 29098, 11488, 56

closes https://github.com/official-stockfish/Stockfish/pull/6071

Bench: 2007023
---
 src/movepick.cpp | 22 +++++++++-------------
 src/movepick.h   |  2 +-
 2 files changed, 10 insertions(+), 14 deletions(-)

diff --git a/src/movepick.cpp b/src/movepick.cpp
index 1c278147f..b0059bd31 100644
--- a/src/movepick.cpp
+++ b/src/movepick.cpp
@@ -208,8 +208,6 @@ Move MovePicker::select(Pred filter) {
 // picking the move with the highest score from a list of generated moves.
 Move MovePicker::next_move() {
 
-    auto quiet_threshold = [](Depth d) { return -3560 * d; };
-
 top:
     switch (stage)
     {
@@ -250,24 +248,22 @@ top:
     case QUIET_INIT :
         if (!skipQuiets)
         {
-            endMoves = beginBadQuiets = endBadQuiets = generate<QUIETS>(pos, cur);
+            cur = endBadQuiets = endBadCaptures;
+            endMoves = generate<QUIETS>(pos, cur);
 
             score<QUIETS>();
-            partial_insertion_sort(cur, endMoves, quiet_threshold(depth));
+            partial_insertion_sort(cur, endMoves, -3560 * depth);
         }
 
         ++stage;
         [[fallthrough]];
 
     case GOOD_QUIET :
-        if (!skipQuiets && select([]() { return true; }))
-        {
-            if ((cur - 1)->value > -7998 || (cur - 1)->value <= quiet_threshold(depth))
-                return *(cur - 1);
-
-            // Remaining quiets are bad
-            beginBadQuiets = cur - 1;
-        }
+        if (!skipQuiets && select([&]() {
+                return cur->value > -14000 ? true
+                                           : (*endBadQuiets++ = *cur, false);
+            }))
+            return *(cur - 1);
 
         // Prepare the pointers to loop over the bad captures
         cur      = moves;
@@ -281,7 +277,7 @@ top:
             return *(cur - 1);
 
         // Prepare the pointers to loop over the bad quiets
-        cur      = beginBadQuiets;
+        cur      = endBadCaptures;
         endMoves = endBadQuiets;
 
         ++stage;
diff --git a/src/movepick.h b/src/movepick.h
index 72a6f4e1c..7da7c3a7e 100644
--- a/src/movepick.h
+++ b/src/movepick.h
@@ -68,7 +68,7 @@ class MovePicker {
     const PieceToHistory**       continuationHistory;
     const PawnHistory*           pawnHistory;
     Move                         ttMove;
-    ExtMove *                    cur, *endMoves, *endBadCaptures, *beginBadQuiets, *endBadQuiets;
+    ExtMove *                    cur, *endMoves, *endBadCaptures, *endBadQuiets;
     int                          stage;
     int                          threshold;
     Depth                        depth;