From: Lucas Braesch <lucas.braesch@gmail.com>
Date: Thu, 21 Feb 2013 14:54:06 +0000 (-0500)
Subject: Prune negative SEE moves also in PV nodes
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=335b57b5ef85da22b7e26cdfc1fd7b3e28dbbe8d;hp=9a1d5f0f1d8a12a85b198688d4f1d636a146eb7a

Prune negative SEE moves also in PV nodes

This patch is actually the sum of two contributions that
have been tested independently:

1) Pruning of negative SEE moves in PV

After 10000 games at 20+0.05
ELO: 5.18 +-7 (95%) LOS: 99.2%
Total: 10000 W: 1952 L: 1803 D: 6245

2) Remove of bestValue > VALUE_MATED_IN_MAX_PLY condition

After 23000 games at 20+0.05
ELO: 1.63 +-4 (95%) LOS: 88.1%
Total: 23000 W: 4232 L: 4124 D: 14644

The whole patch as been re-tested at long TC with positive results:

After 10000 games at 60+0.05
ELO: 4.31 +-7 (95%) LOS: 98.3%
Total: 10000 W: 1765 L: 1641 D: 6594
---

diff --git a/src/search.cpp b/src/search.cpp
index c256cfc0..c039b64e 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -857,16 +857,15 @@ split_point_start: // At split points actual search starts from here
       newDepth = depth - ONE_PLY + ext;
 
       // Step 13. Futility pruning (is omitted in PV nodes)
-      if (   !PvNode
-          && !captureOrPromotion
+      if (   !captureOrPromotion
           && !inCheck
           && !dangerous
           &&  move != ttMove
-          && (bestValue > VALUE_MATED_IN_MAX_PLY || (   bestValue == -VALUE_INFINITE
-                                                     && alpha > VALUE_MATED_IN_MAX_PLY)))
+          &&  alpha > VALUE_MATED_IN_MAX_PLY)
       {
           // Move count based pruning
-          if (   depth < 16 * ONE_PLY
+          if (   !PvNode
+              && depth < 16 * ONE_PLY
               && moveCount >= FutilityMoveCounts[depth]
               && (!threatMove || !refutes(pos, move, threatMove)))
           {
@@ -883,7 +882,7 @@ split_point_start: // At split points actual search starts from here
           futilityValue =  ss->staticEval + ss->evalMargin + futility_margin(predictedDepth, moveCount)
                          + Gain[pos.piece_moved(move)][to_sq(move)];
 
-          if (futilityValue < beta)
+          if (!PvNode && futilityValue < beta)
           {
               if (SpNode)
                   sp->mutex.lock();