Futility tweak

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 9be0bada8c0ee050d7ef0059b1d0af8ed8e565a7..489422fc96f163770aa71791f987baa6d4b0a8a4 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -481,6 +481,19 @@ namespace {
   // evaluate_threats() assigns bonuses according to the types of the attacking
   // and the attacked pieces.
 
+  const Bitboard WhiteCamp = Rank4BB | Rank5BB | Rank6BB | Rank7BB | Rank8BB;
+  const Bitboard BlackCamp = Rank5BB | Rank4BB | Rank3BB | Rank2BB | Rank1BB;
+  const Bitboard QueenSide   = FileABB | FileBBB | FileCBB | FileDBB;
+  const Bitboard CenterFiles = FileCBB | FileDBB | FileEBB | FileFBB;
+  const Bitboard KingSide    = FileEBB | FileFBB | FileGBB | FileHBB;
+
+  const Bitboard KingFlank[COLOR_NB][FILE_NB] = {
+    { QueenSide   & WhiteCamp, QueenSide & WhiteCamp, QueenSide & WhiteCamp, CenterFiles & WhiteCamp,
+      CenterFiles & WhiteCamp, KingSide  & WhiteCamp, KingSide  & WhiteCamp, KingSide    & WhiteCamp },
+    { QueenSide   & BlackCamp, QueenSide & BlackCamp, QueenSide & BlackCamp, CenterFiles & BlackCamp,
+      CenterFiles & BlackCamp, KingSide  & BlackCamp, KingSide  & BlackCamp, KingSide    & BlackCamp },
+  };
+
   template<Color Us, bool DoTrace>
   Score evaluate_threats(const Position& pos, const EvalInfo& ei) {
 
@@ -558,6 +571,18 @@ namespace {
 
     score += ThreatByPawnPush * popcount(b);
 
+    // King tropism: firstly, find squares that we attack in the enemy king flank
+    b = ei.attackedBy[Us][ALL_PIECES] & KingFlank[Us][file_of(pos.square<KING>(Them))];
+
+    // Secondly, add to the bitboard the squares which we attack twice in that flank
+    // but which are not protected by a enemy pawn. Note the trick to shift away the
+    // previous attack bits to the empty part of the bitboard.
+    b =  (b & ei.attackedBy2[Us] & ~ei.attackedBy[Them][PAWN])
+       | (Us == WHITE ? b >> 4 : b << 4);
+
+    // Count all these squares with a single popcount
+    score += make_score(7 * popcount(b), 0);
+
     if (DoTrace)
         Trace::add(THREAT, Us, score);