Capping stat bonus at 2000

snicolet · snicolet · commit 54a989930ebe · 2021-10-06T12:04:35.000+02:00
This patch updates the stat_bonus() function (used in the history tables to help move ordering), keeping the same quadratic for small depths but changing the values for depth >= 9: The old bonus formula was increasing from zero at depth 1 to 4100 at depth 14, then used the strange, small value of 73 for all depths >= 15. The new bonus formula increases from 0 at depth 1 to 2000 at depth 8, then keeps 2000 for all depths >= 8. passed STC: LLR: 2.94 (-2.94,2.94) <-0.50,2.50> Total: 169624 W: 42875 L: 42454 D: 84295 Ptnml(0-2): 585, 19340, 44557, 19729, 601 https://tests.stockfishchess.org/tests/view/615bd69e9d256038a969b97c passed LTC: LLR: 3.07 (-2.94,2.94) <0.50,3.50> Total: 37336 W: 9456 L: 9191 D: 18689 Ptnml(0-2): 20, 3810, 10747, 4067, 24 https://tests.stockfishchess.org/tests/view/615c75d99d256038a969b9b2 closes #3731 Bench: 6261865
diff --git a/src/search.cpp b/src/search.cpp
@@ -80,7 +80,7 @@ namespace {
 
   // History and stats update bonus, based on depth
   int stat_bonus(Depth d) {
-    return d > 14 ? 73 : 6 * d * d + 229 * d - 215;
+    return std::min((6 * d + 229) * d - 215 , 2000);
   }
 
   // Add a small random component to draw evaluations to avoid 3-fold blindness
@@ -1709,8 +1709,8 @@ namespace {
     PieceType captured = type_of(pos.piece_on(to_sq(bestMove)));
 
     bonus1 = stat_bonus(depth + 1);
-    bonus2 = bestValue > beta + PawnValueMg ? bonus1                                 // larger bonus
-                                            : std::min(bonus1, stat_bonus(depth));   // smaller bonus
+    bonus2 = bestValue > beta + PawnValueMg ? bonus1               // larger bonus
+                                            : stat_bonus(depth);   // smaller bonus
 
     if (!pos.capture_or_promotion(bestMove))
     {
