History Pruning: Don't prune the main killer move.

Also increased pruned depth to 4.

STC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 23380 W: 4581 L: 4350 D: 14449

LTC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 28934 W: 4329 L: 4105 D: 20500

Bench: 8369743

Resolves #498

diff --git a/src/search.cpp b/src/search.cpp
index 13fb4b300936492657ee375d0d14c3e9bf460e46..4a0302e51f9e7087d72892bdc23e84339ddef191 100644 (file)
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -921,7 +921,8 @@ moves_loop: // When in check search starts from here
               continue;
 
           // History based pruning
-          if (   depth <= 3 * ONE_PLY
+          if (   depth <= 4 * ONE_PLY
+              && move != ss->killers[0]
               && thisThread->history[pos.moved_piece(move)][to_sq(move)] < VALUE_ZERO
               && cmh[pos.moved_piece(move)][to_sq(move)] < VALUE_ZERO)
               continue;