From b7ecdaada7e2690dd286c41d3a73463f06fb088f Mon Sep 17 00:00:00 2001
From: Praveen tummala <praveentummala@Praveens-MacBook-Pro.local>
Date: Mon, 30 Mar 2020 10:22:42 +0530
Subject: [PATCH 1/1] Movecount pruning reduction logic

This patch refines search reduction logic in case the position is not a former PV node and is pruned based on move count.

passed STC
https://tests.stockfishchess.org/tests/view/5e8092bde42a5c3b3ca2ed35
LLR: 2.94 (-2.94,2.94) {-0.50,1.50}
Total: 78848 W: 15480 L: 15170 D: 48198
Ptnml(0-2): 1406, 9310, 17773, 9438, 1497

passed LTC
https://tests.stockfishchess.org/tests/view/5e80bb13e42a5c3b3ca2ed4b
LLR: 2.94 (-2.94,2.94) {0.25,1.75}
Total: 86596 W: 11451 L: 11033 D: 64112
Ptnml(0-2): 624, 7993, 25687, 8329, 665

closes https://github.com/official-stockfish/Stockfish/pull/2605

Bench: 5138771
---
 AUTHORS        |  3 ++-
 src/search.cpp | 10 +++++++---
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/AUTHORS b/AUTHORS
index 4826d1c4..79eb98a0 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -1,4 +1,4 @@
-# List of authors for Stockfish, as of January 7, 2020
+# List of authors for Stockfish, as of March 30, 2020
 
 Tord Romstad (romstad)
 Marco Costalba (mcostalba)
@@ -123,6 +123,7 @@ Pasquale Pigazzini (ppigazzini)
 Patrick Jansen (mibere)
 pellanda
 Peter Zsifkovits (CoffeeOne)
+Praveen Kumar Tummala (praveentml)
 Rahul Dsilva (silversolver1)
 Ralph Stößer (Ralph Stoesser)
 Raminder Singh
diff --git a/src/search.cpp b/src/search.cpp
index f866afe5..993fa853 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -962,6 +962,7 @@ moves_loop: // When in check, search starts from here
     value = bestValue;
     singularLMR = moveCountPruning = false;
     ttCapture = ttMove && pos.capture_or_promotion(ttMove);
+    bool formerPv = ttPv && !PvNode;
 
     // Mark this node as being searched
     ThreadHolding th(thisThread, posKey, ss->ply);
@@ -1054,8 +1055,8 @@ moves_loop: // When in check, search starts from here
           &&  tte->depth() >= depth - 3
           &&  pos.legal(move))
       {
-          Value singularBeta = ttValue - (((ttPv && !PvNode) + 4) * depth) / 2;
-          Depth singularDepth = (depth - 1 + 3 * (ttPv && !PvNode)) / 2;
+          Value singularBeta = ttValue - ((formerPv + 4) * depth) / 2;
+          Depth singularDepth = (depth - 1 + 3 * formerPv) / 2;
           ss->excludedMove = move;
           value = search<NonPV>(pos, ss, singularBeta - 1, singularBeta, singularDepth, cutNode);
           ss->excludedMove = MOVE_NONE;
@@ -1143,13 +1144,16 @@ moves_loop: // When in check, search starts from here
           if (ttPv)
               r -= 2;
 
+          if (moveCountPruning && !formerPv)
+              r++;
+
           // Decrease reduction if opponent's move count is high (~5 Elo)
           if ((ss-1)->moveCount > 14)
               r--;
 
           // Decrease reduction if ttMove has been singularly extended (~3 Elo)
           if (singularLMR)
-              r -= 1 + (ttPv && !PvNode);
+              r -= 1 + formerPv;
 
           if (!captureOrPromotion)
           {
-- 
2.39.2