Remove candidate passers w/o feasible lever

[stockfish] / src / evaluate.cpp

diff --git a/src/evaluate.cpp b/src/evaluate.cpp
index d51325f0d990c84fc0aa231ec7a495a9902491e3..2698c813dfab118e78a37d1d70d8d1584c4d1e59 100644 (file)
--- a/src/evaluate.cpp
+++ b/src/evaluate.cpp
@@ -91,15 +91,15 @@ namespace {
   // MobilityBonus[PieceType-2][attacked] contains bonuses for middle and end game,
   // indexed by piece type and number of attacked squares in the mobility area.
   constexpr Score MobilityBonus[][32] = {
-    { S(-62,-81), S(-53,-56), S(-12,-30), S( -4,-14), S(  3,  8), S( 13, 15), // Knights
+    { S(-62,-81), S(-53,-56), S(-12,-30), S( -4,-14), S(  3,  8), S( 13, 15), // Knight
       S( 22, 23), S( 28, 27), S( 33, 33) },
-    { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishops
+    { S(-48,-59), S(-20,-23), S( 16, -3), S( 26, 13), S( 38, 24), S( 51, 42), // Bishop
       S( 55, 54), S( 63, 57), S( 63, 65), S( 68, 73), S( 81, 78), S( 81, 86),
       S( 91, 88), S( 98, 97) },
-    { S(-58,-76), S(-27,-18), S(-15, 28), S(-10, 55), S( -5, 69), S( -2, 82), // Rooks
+    { S(-58,-76), S(-27,-18), S(-15, 28), S(-10, 55), S( -5, 69), S( -2, 82), // Rook
       S(  9,112), S( 16,118), S( 30,132), S( 29,142), S( 32,155), S( 38,165),
       S( 46,166), S( 48,169), S( 58,171) },
-    { S(-39,-36), S(-21,-15), S(  3,  8), S(  3, 18), S( 14, 34), S( 22, 54), // Queens
+    { S(-39,-36), S(-21,-15), S(  3,  8), S(  3, 18), S( 14, 34), S( 22, 54), // Queen
       S( 28, 61), S( 41, 73), S( 43, 79), S( 48, 92), S( 56, 94), S( 60,104),
       S( 60,113), S( 66,120), S( 67,123), S( 70,126), S( 71,133), S( 73,136),
       S( 79,140), S( 88,143), S( 88,148), S( 99,166), S(102,170), S(102,175),
@@ -213,7 +213,7 @@ namespace {
   template<Tracing T> template<Color Us>
   void Evaluation<T>::initialize() {
 
-    constexpr Color     Them = (Us == WHITE ? BLACK : WHITE);
+    constexpr Color     Them = ~Us;
     constexpr Direction Up   = pawn_push(Us);
     constexpr Direction Down = -Up;
     constexpr Bitboard LowRanks = (Us == WHITE ? Rank2BB | Rank3BB : Rank7BB | Rank6BB);
@@ -252,7 +252,7 @@ namespace {
   template<Tracing T> template<Color Us, PieceType Pt>
   Score Evaluation<T>::pieces() {
 
-    constexpr Color     Them = (Us == WHITE ? BLACK : WHITE);
+    constexpr Color     Them = ~Us;
     constexpr Direction Down = -pawn_push(Us);
     constexpr Bitboard OutpostRanks = (Us == WHITE ? Rank4BB | Rank5BB | Rank6BB
                                                    : Rank5BB | Rank4BB | Rank3BB);
@@ -298,12 +298,12 @@ namespace {
             else if (Pt == KNIGHT && bb & b & ~pos.pieces(Us))
                 score += Outpost;
 
-            // Knight and Bishop bonus for being right behind a pawn
+            // Bonus for a knight or bishop shielded by pawn
             if (shift<Down>(pos.pieces(PAWN)) & s)
                 score += MinorBehindPawn;
 
             // Penalty if the piece is far from the king
-            score -= KingProtector * distance(s, pos.square<KING>(Us));
+            score -= KingProtector * distance(pos.square<KING>(Us), s);
 
             if (Pt == BISHOP)
             {
@@ -313,7 +313,7 @@ namespace {
                 Bitboard blocked = pos.pieces(Us, PAWN) & shift<Down>(pos.pieces());
 
                 score -= BishopPawns * pos.pawns_on_same_color_squares(Us, s)
-                                     * (!bool(attackedBy[Us][PAWN] & s) + popcount(blocked & CenterFiles));
+                                     * (!(attackedBy[Us][PAWN] & s) + popcount(blocked & CenterFiles));
 
                 // Bonus for bishop on a long diagonal which can "see" both center squares
                 if (more_than_one(attacks_bb<BISHOP>(s, pos.pieces(PAWN)) & Center))
@@ -372,7 +372,7 @@ namespace {
   template<Tracing T> template<Color Us>
   Score Evaluation<T>::king() const {
 
-    constexpr Color    Them = (Us == WHITE ? BLACK : WHITE);
+    constexpr Color    Them = ~Us;
     constexpr Bitboard Camp = (Us == WHITE ? AllSquares ^ Rank6BB ^ Rank7BB ^ Rank8BB
                                            : AllSquares ^ Rank1BB ^ Rank2BB ^ Rank3BB);
 
@@ -480,7 +480,7 @@ namespace {
   template<Tracing T> template<Color Us>
   Score Evaluation<T>::threats() const {
 
-    constexpr Color     Them     = (Us == WHITE ? BLACK   : WHITE);
+    constexpr Color     Them     = ~Us;
     constexpr Direction Up       = pawn_push(Us);
     constexpr Bitboard  TRank3BB = (Us == WHITE ? Rank3BB : Rank6BB);
 
@@ -576,18 +576,35 @@ namespace {
   template<Tracing T> template<Color Us>
   Score Evaluation<T>::passed() const {
 
-    constexpr Color     Them = (Us == WHITE ? BLACK : WHITE);
+    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));
     }
 
@@ -667,7 +678,7 @@ namespace {
     if (pos.non_pawn_material() < SpaceThreshold)
         return SCORE_ZERO;
 
-    constexpr Color Them     = (Us == WHITE ? BLACK : WHITE);
+    constexpr Color Them     = ~Us;
     constexpr Direction Down = -pawn_push(Us);
     constexpr Bitboard SpaceMask =
       Us == WHITE ? CenterFiles & (Rank2BB | Rank3BB | Rank4BB)
@@ -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));