CMH Pruning Tweak

Tweak pruning formula by adding up CMH values.

STC:
LLR: 2.94 (-2.94,2.94) <-0.50,2.50>
Total: 14608 W: 3837 L: 3641 D: 7130
Ptnml(0-2): 27, 1681, 3723, 1815, 58
https://tests.stockfishchess.org/tests/view/612792f362d20cf82b5ad156

LTC:
LLR: 2.94 (-2.94,2.94) <0.50,3.50>
Total: 53520 W: 13580 L: 13276 D: 26664
Ptnml(0-2): 28, 5610, 15183, 5908, 31
https://tests.stockfishchess.org/tests/view/6127d27062d20cf82b5ad191

closes https://github.com/official-stockfish/Stockfish/pull/3682

Bench: 5186641

diff --git a/src/search.cpp b/src/search.cpp
index a487ed1305b1ccdc8aabe5b42858ec71799b5895..5aa506446c3f68ef7474e4ecd49709714926c622 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1018,9 +1018,10 @@ moves_loop: // When in check, search starts here
           else
           {
               // Continuation history based pruning (~20 Elo)
           else
           {
               // Continuation history based pruning (~20 Elo)

-              if (   lmrDepth < 5
-                  && (*contHist[0])[movedPiece][to_sq(move)] < 23 - 23 * depth * depth
-                  && (*contHist[1])[movedPiece][to_sq(move)] < 23 - 23 * depth * depth)
+              if (lmrDepth < 5
+                  && (*contHist[0])[movedPiece][to_sq(move)]
+                  + (*contHist[1])[movedPiece][to_sq(move)]
+                  + (*contHist[3])[movedPiece][to_sq(move)] < -3000 * depth + 3000)

                   continue;
 
               // Futility pruning: parent node (~5 Elo)
                   continue;
 
               // Futility pruning: parent node (~5 Elo)