Account for enemy pawn attacks in mobility

Elo   | 14.90 +- 7.93 (95%)
SPRT  | 8.0+0.08s Threads=1 Hash=16MB
LLR   | 2.96 (-2.94, 2.94) [0.00, 5.00]
Games | N: 4084 W: 1379 L: 1204 D: 1501
Penta | [135, 442, 776, 491, 198]

CHANGELOG.md

@@ -3,6 +3,7 @@
 ## [Unreleased]
 
 * Evaluate passed pawns (38.30 +- 13.27)
+* Don't consider mobility for squares that are attacked by opponent pawns (14.90 +- 7.93)
 
 ## [5.0]
 

src/engine/eval/mobility_and_king_safety.rs

@@ -11,30 +11,42 @@ fn mobility_and_opp_king_safety_for(game: &Game, player: Player) -> PhasedEval {
     let mut eval = PhasedEval::ZERO;
     let blockers = game.board.occupancy();
 
+    let their_pawns = game.board.pawns(player.other()).forward(player.other());
+    let their_pawn_attacks = their_pawns.west() | their_pawns.east();
+    let mobility_safe_squares = !their_pawn_attacks;
+
     let mut attacked_squares = Bitboard::EMPTY;
 
     for p in game.board.knights(player) {
         let moves = tables::knight_attacks(p);
         attacked_squares |= moves;
-        eval += KNIGHT_MOBILITY[moves.count() as usize];
+
+        let mobility_squares = (moves & mobility_safe_squares).count() as usize;
+        eval += KNIGHT_MOBILITY[mobility_squares];
     }
 
     for p in game.board.bishops(player) {
         let moves = tables::bishop_attacks(p, blockers);
         attacked_squares |= moves;
-        eval += BISHOP_MOBILITY[moves.count() as usize];
+
+        let mobility_squares = (moves & mobility_safe_squares).count() as usize;
+        eval += BISHOP_MOBILITY[mobility_squares];
     }
 
     for p in game.board.rooks(player) {
         let moves = tables::rook_attacks(p, blockers);
         attacked_squares |= moves;
-        eval += ROOK_MOBILITY[moves.count() as usize];
+
+        let mobility_squares = (moves & mobility_safe_squares).count() as usize;
+        eval += ROOK_MOBILITY[mobility_squares];
     }
 
     for p in game.board.queens(player) {
         let moves = tables::bishop_attacks(p, blockers) | tables::rook_attacks(p, blockers);
         attacked_squares |= moves;
-        eval += QUEEN_MOBILITY[moves.count() as usize];
+
+        let mobility_squares = (moves & mobility_safe_squares).count() as usize;
+        eval += QUEEN_MOBILITY[mobility_squares];
     }
 
     let enemy_king = game.board.king(player.other()).single();