X-Git-Url: https://git.sesse.net/?p=stockfish;a=blobdiff_plain;f=src%2Fmovepick.h;h=96986c84658723667b024f90627d3f221e24573f;hp=93061ee6fc6a81c8aaf277b817dab41a0d02dd34;hb=c9dcda6ac488c0058ebd567e1f52e30b8cd0db20;hpb=eed508b4445057cd26bfb95ab5cd754ac96629fd

diff --git a/src/movepick.h b/src/movepick.h
index 93061ee6..96986c84 100644
--- a/src/movepick.h
+++ b/src/movepick.h
@@ -1,7 +1,7 @@
 /*
   Stockfish, a UCI chess playing engine derived from Glaurung 2.1
   Copyright (C) 2004-2008 Tord Romstad (Glaurung author)
-  Copyright (C) 2008-2013 Marco Costalba, Joona Kiiski, Tord Romstad
+  Copyright (C) 2008-2014 Marco Costalba, Joona Kiiski, Tord Romstad
 
   Stockfish is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
@@ -30,13 +30,14 @@
 
 
 /// The Stats struct stores moves statistics. According to the template parameter
-/// the class can store History and Countermoves. History records how often
+/// the class can store History, Gains and Countermoves. History records how often
 /// different moves have been successful or unsuccessful during the current search
-/// and is used for reduction and move ordering decisions.
+/// and is used for reduction and move ordering decisions. Gains records the move's
+/// best evaluation gain from one ply to the next and is used for pruning decisions.
 /// Countermoves store the move that refute a previous one. Entries are stored
-/// according only to moving piece and destination square, hence two moves with
+/// using only the moving piece and destination square, hence two moves with
 /// different origin but same destination and piece will be considered identical.
-template<typename T>
+template<bool Gain, typename T>
 struct Stats {
 
   static const Value Max = Value(2000);
@@ -55,7 +56,10 @@ struct Stats {
 
   void update(Piece p, Square to, Value v) {
 
-    if (abs(table[p][to] + v) < Max)
+    if (Gain)
+        table[p][to] = std::max(v, table[p][to] - 1);
+
+    else if (abs(table[p][to] + v) < Max)
         table[p][to] +=  v;
   }
 
@@ -63,8 +67,9 @@ private:
   T table[PIECE_NB][SQUARE_NB];
 };
 
-typedef Stats<Value> HistoryStats;
-typedef Stats<std::pair<Move, Move> > CountermovesStats;
+typedef Stats< true, Value> GainsStats;
+typedef Stats<false, Value> HistoryStats;
+typedef Stats<false, std::pair<Move, Move> > CountermovesStats;
 
 
 /// MovePicker class is used to pick one pseudo legal move at a time from the