From: VoyagerOne <excelgeek@gmail.com>
Date: Mon, 22 May 2017 01:25:20 +0000 (-0700)
Subject: Evasion Pruning Tweak
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=1d31065e1d1f04ecf47fc959523c560e8657fbfa;hp=c216dcbe7bfc5e326d260d1b7c1271fb4ffc67c9

Evasion Pruning Tweak

Use moveCount to decide when to prune for evasion pruning

STC:
LLR: 2.95 (-2.94,2.94) [0.00,5.00]
Total: 24476 W: 4518 L: 4289 D: 15669

LTC:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 18362 W: 2476 L: 2298 D: 13588

Bench: 6469989

Closes #1120
---

diff --git a/src/search.cpp b/src/search.cpp
index de487e57..2e8d5c6f 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1165,6 +1165,7 @@ moves_loop: // When in check search starts from here
     Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
     bool ttHit, givesCheck, evasionPrunable;
     Depth ttDepth;
+    int moveCount;
 
     if (PvNode)
     {
@@ -1175,6 +1176,7 @@ moves_loop: // When in check search starts from here
 
     ss->currentMove = bestMove = MOVE_NONE;
     ss->ply = (ss-1)->ply + 1;
+    moveCount = 0;
 
     // Check for an instant draw or if the maximum ply has been reached
     if (pos.is_draw(ss->ply) || ss->ply >= MAX_PLY)
@@ -1258,6 +1260,8 @@ moves_loop: // When in check search starts from here
                   ? pos.check_squares(type_of(pos.piece_on(from_sq(move)))) & to_sq(move)
                   : pos.gives_check(move);
 
+      moveCount++;
+
       // Futility pruning
       if (   !InCheck
           && !givesCheck
@@ -1283,7 +1287,7 @@ moves_loop: // When in check search starts from here
 
       // Detect non-capture evasions that are candidates to be pruned
       evasionPrunable =    InCheck
-                       &&  depth != DEPTH_ZERO
+                       &&  (depth != DEPTH_ZERO || moveCount > 2)
                        &&  bestValue > VALUE_MATED_IN_MAX_PLY
                        && !pos.capture(move);
 
@@ -1298,7 +1302,10 @@ moves_loop: // When in check search starts from here
 
       // Check for legality just before making the move
       if (!pos.legal(move))
+      {
+          moveCount--;
           continue;
+      }
 
       ss->currentMove = move;