Introduce tropism measure in king danger

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 964a3870b7ded986f721b46f35fab93f23332e77..c54b6d30bc81eed71e2582bfa7704cfc1da34739 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -413,11 +413,19 @@ namespace {
                                            : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
 
     const Square ksq = pos.square<KING>(Us);
-    Bitboard weak, b, b1, b2, safe, unsafeChecks;
+    Bitboard kingFlank, weak, b, b1, b2, safe, unsafeChecks;
 
     // King shelter and enemy pawns storm
     Score score = pe->king_safety<Us>(pos, ksq);
 
+    // Find the squares that opponent attacks in our king flank, and the squares
+    // which are attacked twice in that flank but not defended by our pawns.
+    kingFlank = KingFlank[file_of(ksq)];
+    b1 = attackedBy[Them][ALL_PIECES] & kingFlank & Camp;
+    b2 = b1 & attackedBy2[Them] & ~attackedBy[Us][PAWN];
+
+    int tropism = popcount(b1) + popcount(b2);
+
     // Main king safety evaluation
     if (kingAttackersCount[Them] > 1 - pos.count<QUEEN>(Them))
     {
@@ -470,9 +478,10 @@ namespace {
                      +  69 * kingAttacksCount[Them]
                      + 185 * popcount(kingRing[Us] & weak)
                      + 129 * popcount(pos.blockers_for_king(Us) | unsafeChecks)
+                     +   4 * tropism
                      - 873 * !pos.count<QUEEN>(Them)
                      -   6 * mg_value(score) / 8
-                     -   2 ;
+                     -   30;
 
         // Transform the kingDanger units into a Score, and subtract it from the evaluation
         if (kingDanger > 0)
@@ -483,19 +492,12 @@ namespace {
         }
     }
 
-    Bitboard kf = KingFlank[file_of(ksq)];
-
     // Penalty when our king is on a pawnless flank
-    if (!(pos.pieces(PAWN) & kf))
+    if (!(pos.pieces(PAWN) & kingFlank))
         score -= PawnlessFlank;
 
-    // Find the squares that opponent attacks in our king flank, and the squares
-    // which are attacked twice in that flank but not defended by our pawns.
-    b1 = attackedBy[Them][ALL_PIECES] & kf & Camp;
-    b2 = b1 & attackedBy2[Them] & ~attackedBy[Us][PAWN];
-
-    // King tropism, to anticipate slow motion attacks on our king
-    score -= CloseEnemies * (popcount(b1) + popcount(b2));
+    // King tropism bonus, to anticipate slow motion attacks on our king
+    score -= CloseEnemies * tropism;
 
     if (T)
         Trace::add(KING, Us, score);