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

diff --git a/AUTHORS b/AUTHORS
index 4826d1c4c3c03c13975bf631e6094cb28a6f6137..79eb98a0b537d4a6ade6317d402035d08da35ff7 100644 (file)
--- 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)
 
 Tord Romstad (romstad)
 Marco Costalba (mcostalba)


@@ -123,6 +123,7 @@ Pasquale Pigazzini (ppigazzini)
 Patrick Jansen (mibere)
 pellanda
 Peter Zsifkovits (CoffeeOne)
 Patrick Jansen (mibere)
 pellanda
 Peter Zsifkovits (CoffeeOne)

+Praveen Kumar Tummala (praveentml)

 Rahul Dsilva (silversolver1)
 Ralph Stößer (Ralph Stoesser)
 Raminder Singh
 Rahul Dsilva (silversolver1)
 Ralph Stößer (Ralph Stoesser)
 Raminder Singh

diff --git a/src/search.cpp b/src/search.cpp
index f866afe5ce7b887747e80da04e79c6593a8713f2..993fa853f47ce51d95c167ae3c951f70fce4f27b 100644 (file)
--- 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);
     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);
 
     // 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))
       {
           &&  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;
           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 (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)
           // 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)
           {
 
           if (!captureOrPromotion)
           {