Tweak capture scoring formula

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 3ff1460b562742a12c3f79883839d3b7db69e914..f2e822d0b6b9f1dd65e70ff911880516bf05753c 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -133,6 +133,7 @@ namespace {
   };
 
   // Assorted bonuses and penalties
+  constexpr Score AttacksOnSpaceArea = S(  4,  0);
   constexpr Score BishopPawns        = S(  3,  7);
   constexpr Score CorneredBishop     = S( 50, 50);
   constexpr Score FlankAttacks       = S(  8,  0);
@@ -635,10 +636,8 @@ namespace {
             // If the pawn is free to advance, then increase the bonus
             if (pos.empty(blockSq))
             {
-                // If there is a rook or queen attacking/defending the pawn from behind,
-                // consider all the squaresToQueen. Otherwise consider only the squares
-                // in the pawn's path attacked or occupied by the enemy.
-                defendedSquares = unsafeSquares = squaresToQueen = forward_file_bb(Us, s);
+                defendedSquares = squaresToQueen = forward_file_bb(Us, s);
+                unsafeSquares = passed_pawn_span(Us, s);
 
                 bb = forward_file_bb(Them, s) & pos.pieces(ROOK, QUEEN);
 
@@ -648,9 +647,13 @@ namespace {
                 if (!(pos.pieces(Them) & bb))
                     unsafeSquares &= attackedBy[Them][ALL_PIECES] | pos.pieces(Them);
 
-                // If there aren't any enemy attacks, assign a big bonus. Otherwise
-                // assign a smaller bonus if the block square isn't attacked.
-                int k = !unsafeSquares ? 20 : !(unsafeSquares & blockSq) ? 9 : 0;
+                // If there are no enemy attacks on passed pawn span, assign a big bonus.
+                // Otherwise assign a smaller bonus if the path to queen is not attacked
+                // and even smaller bonus if it is attacked but block square is not.
+                int k = !unsafeSquares                    ? 35 :
+                        !(unsafeSquares & squaresToQueen) ? 20 :
+                        !(unsafeSquares & blockSq)        ?  9 :
+                                                             0 ;
 
                 // Assign a larger bonus if the block square is defended.
                 if (defendedSquares & blockSq)
@@ -709,6 +712,8 @@ namespace {
     int weight = pos.count<ALL_PIECES>(Us) - 1;
     Score score = make_score(bonus * weight * weight / 16, 0);
 
+    score -= AttacksOnSpaceArea * popcount(attackedBy[Them][ALL_PIECES] & behind & safe);
+
     if (T)
         Trace::add(SPACE, Us, score);