From 4eca981e557704f4ce3db829adf380b8fc058926 Mon Sep 17 00:00:00 2001
From: VoyagerOne <excelgeek@gmail.com>
Date: Wed, 21 Oct 2015 18:21:23 -0400
Subject: [PATCH 1/1] History pruning

Prune moves with negative History
and CMH scores at low depth.

STC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 24182 W: 4672 L: 4439 D: 15071

LTC:
LLR: 2.97 (-2.94,2.94) [0.00,5.00]
Total: 12579 W: 1959 L: 1792 D: 8828

bench: 8907701
---
 src/search.cpp | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/search.cpp b/src/search.cpp
index 33ab6b5f..b3dc2775 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -894,6 +894,13 @@ moves_loop: // When in check search starts from here
               && moveCount >= FutilityMoveCounts[improving][depth])
               continue;
 
+          // History Score Pruning
+          if (   depth <= 3 * ONE_PLY
+              && thisThread->History[pos.moved_piece(move)][to_sq(move)] < VALUE_ZERO
+              && CounterMovesHistory[pos.piece_on(prevMoveSq)][prevMoveSq]
+                                    [pos.moved_piece(move)][to_sq(move)] < VALUE_ZERO)
+              continue;
+
           predictedDepth = newDepth - reduction<PvNode>(improving, depth, moveCount);
 
           // Futility pruning: parent node
-- 
2.39.2