From: Marco Costalba <mcostalba@gmail.com>
Date: Sat, 1 Dec 2012 17:06:29 +0000 (+0100)
Subject: Reintroduce eval optimizaion from null search
X-Git-Url: https://git.sesse.net/?p=stockfish;a=commitdiff_plain;h=23bdd064426c6fb5b6fd860d156c9f50bb58d0db;hp=98cd8239cc351f337132bb8cf08be728580c078d

Reintroduce eval optimizaion from null search

Now that conversion to eval cache is finished
we can reintroduce this optimization.

bench: 5149248
---

diff --git a/src/search.cpp b/src/search.cpp
index 52e7600b..f6c2233b 100644
--- a/src/search.cpp
+++ b/src/search.cpp
@@ -1090,7 +1090,7 @@ split_point_start: // At split points actual search starts from here
     Key posKey;
     Move ttMove, move, bestMove;
     Value bestValue, value, ttValue, futilityValue, futilityBase, oldAlpha;
-    bool givesCheck, enoughMaterial, evasionPrunable;
+    bool givesCheck, enoughMaterial, evasionPrunable, fromNull;
     Depth ttDepth;
 
     // To flag BOUND_EXACT a node with eval above alpha and no available moves
@@ -1099,6 +1099,7 @@ split_point_start: // At split points actual search starts from here
 
     ss->currentMove = bestMove = MOVE_NONE;
     ss->ply = (ss-1)->ply + 1;
+    fromNull = (ss-1)->currentMove == MOVE_NULL;
 
     // Check for an instant draw or maximum ply reached
     if (pos.is_draw<false, false>() || ss->ply > MAX_PLY)
@@ -1136,7 +1137,14 @@ split_point_start: // At split points actual search starts from here
     }
     else
     {
-        ss->staticEval = bestValue = evaluate(pos, ss->evalMargin);
+        if (fromNull)
+        {
+            // Approximated score. Real one is slightly higher due to tempo
+            ss->staticEval = bestValue = -(ss-1)->staticEval;
+            ss->evalMargin = VALUE_ZERO;
+        }
+        else
+            ss->staticEval = bestValue = evaluate(pos, ss->evalMargin);
 
         // Stand pat. Return immediately if static value is at least beta
         if (bestValue >= beta)
@@ -1171,6 +1179,7 @@ split_point_start: // At split points actual search starts from here
       // Futility pruning
       if (   !PvNode
           && !InCheck
+          && !fromNull
           && !givesCheck
           &&  move != ttMove
           &&  enoughMaterial