Remove candidate passers w/o feasible lever

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index 63541c2affbe00fa56d3477e55a712b83ce4a98d..2698c813dfab118e78a37d1d70d8d1584c4d1e59 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -578,16 +578,33 @@ namespace {
 
     constexpr Color     Them = ~Us;
     constexpr Direction Up   = pawn_push(Us);
+    constexpr Direction Down = -Up;
 
     auto king_proximity = [&](Color c, Square s) {
       return std::min(distance(pos.square<KING>(c), s), 5);
     };
 
-    Bitboard b, bb, squaresToQueen, unsafeSquares;
+    Bitboard b, bb, squaresToQueen, unsafeSquares, candidatePassers, leverable;
     Score score = SCORE_ZERO;
 
     b = pe->passed_pawns(Us);
 
+    candidatePassers = b & shift<Down>(pos.pieces(Them, PAWN));
+    if (candidatePassers)
+    {
+        // Can we lever the blocker of a candidate passer?
+        leverable =  shift<Up>(pos.pieces(Us, PAWN))
+                   & ~pos.pieces(Them)
+                   & (~attackedBy2[Them] | attackedBy[Us][ALL_PIECES])
+                   & (~(attackedBy[Them][KNIGHT] | attackedBy[Them][BISHOP])
+                     | (attackedBy[Us  ][KNIGHT] | attackedBy[Us  ][BISHOP]));
+
+        // Remove candidate otherwise
+        b &= ~candidatePassers
+            | shift<WEST>(leverable)
+            | shift<EAST>(leverable);
+    }
+
     while (b)
     {
         Square s = pop_lsb(&b);
@@ -638,12 +655,6 @@ namespace {
             }
         } // r > RANK_3
 
-        // Scale down bonus for candidate passers which need more than one
-        // pawn push to become passed, or have a pawn in front of them.
-        if (   !pos.pawn_passed(Us, s + Up)
-            || (pos.pieces(PAWN) & (s + Up)))
-            bonus = bonus / 2;
-
         score += bonus - PassedFile * edge_distance(file_of(s));
     }
 
@@ -752,7 +763,7 @@ namespace {
     {
         if (   pos.opposite_bishops()
             && pos.non_pawn_material() == 2 * BishopValueMg)
-            sf = 22 ;
+            sf = 22;
         else
             sf = std::min(sf, 36 + (pos.opposite_bishops() ? 2 : 7) * pos.count<PAWN>(strongSide));