From: VoyagerOne <excelgeek@gmail.com>
Date: Thu, 6 Dec 2018 13:39:41 +0000 (+0100)
Subject: Simplify Killer Move Penalty
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=7b4f9c37cb859ba6258ba90d11358879c0b2c57d

Simplify Killer Move Penalty

STC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 20816 W: 4525 L: 4402 D: 11889
http://tests.stockfishchess.org/tests/view/5c017cb90ebc5902bcede5b4

LTC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 39287 W: 6401 L: 6309 D: 26577
http://tests.stockfishchess.org/tests/view/5c01825e0ebc5902bcede686

Bench: 3773021
---

diff --git a/src/search.cpp b/src/search.cpp
index 6a63fcaa..66843515 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1185,15 +1185,12 @@ moves_loop: // When in check, search starts from here
 
         update_capture_stats(pos, bestMove, capturesSearched, captureCount, stat_bonus(depth + ONE_PLY));
 
-        // Extra penalty for a quiet TT move in previous ply when it gets refuted
-        if ((ss-1)->moveCount == 1 && !pos.captured_piece())
-            update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
-
-        // Extra penalty for killer move in previous ply when it gets refuted
-        else if (  (ss-1)->killers[0]
-                && (ss-1)->currentMove == (ss-1)->killers[0]
-                && !pos.captured_piece())
-            update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth));
+        // Extra penalty for a quiet TT or main killer move in previous ply when it gets refuted
+		if (   (ss-1)->moveCount == 1
+		    || ((ss-1)->currentMove == (ss-1)->killers[0] && (ss-1)->killers[0]))
+		    if (!pos.captured_piece())
+                update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -stat_bonus(depth + ONE_PLY));
+
     }
     // Bonus for prior countermove that caused the fail low
     else if (   (depth >= 3 * ONE_PLY || PvNode)