Adjust reductions

Decrease further on cutNodes with tte->depth() >= depth + 3 condition.

LTC: https://tests.stockfishchess.org/tests/view/644dc84bccf5e93df5e50c13
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 155346 W: 42184 L: 41660 D: 71502
Ptnml(0-2): 59, 14765, 47504, 15283, 62

STC: https://tests.stockfishchess.org/tests/view/644d05de68e01d8194cd9bbb
LLR: 2.93 (-2.94,2.94) <0.00,2.00>
Total: 121888 W: 32868 L: 32444 D: 56576
Ptnml(0-2): 332, 13273, 33343, 13631, 365

closes https://github.com/official-stockfish/Stockfish/pull/4552

bench: 3739675

diff --git a/src/search.cpp b/src/search.cpp
index 8ce9c56e42d0849e2caf9b2528d463faf524fe21..a6618c5b815f8c7719658794c1a8e11ce8de336d 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -884,7 +884,7 @@ namespace {
     // Use qsearch if depth is equal or below zero (~9 Elo)
     if (    PvNode
         && !ttMove)
-        depth -= 2 + 2 * (ss->ttHit &&  tte->depth() >= depth);
+        depth -= 2 + 2 * (ss->ttHit && tte->depth() >= depth);
 
     if (depth <= 0)
         return qsearch<PV>(pos, ss, alpha, beta);
@@ -1141,9 +1141,10 @@ moves_loop: // When in check, search starts here
 
       // Decrease reduction if position is or has been on the PV
       // and node is not likely to fail low. (~3 Elo)
+      // Decrease further on cutNodes. (~1 Elo)
       if (   ss->ttPv
           && !likelyFailLow)
-          r -= 2;
+          r -= cutNode && tte->depth() >= depth + 3 ? 3 : 2;
 
       // Decrease reduction if opponent's move count is high (~1 Elo)
       if ((ss-1)->moveCount > 7)