Evaluate king safety

Evaluate by attacks on the squares around the king.

Elo   | 24.27 +- 10.43 (95%)
SPRT  | 8.0+0.08s Threads=1 Hash=16MB
LLR   | 3.00 (-2.94, 2.94) [0.00, 5.00]
Games | N: 2452 W: 864 L: 693 D: 895
Penta | [78, 248, 464, 297, 139]

CHANGELOG.md

@@ -5,6 +5,7 @@
 * Tune all evaluation parameters with https://github.com/GediminasMasaitis/texel-tuner (53.17 +- 16.76)
 * Evaluate piece mobility (41.36 +- 13.82)
 * Add a texel tuner in-repo and tune, resolving an issue where mobility scores were not computed correctly (28.53 +- 11.44)
+* Evaluate king safety (24.27 +- 10.43)
 
 ### Misc
 

src/engine/eval/mobility_and_king_safety.rs

@@ -0,0 +1,52 @@
+use super::PhasedEval;
+use crate::chess::bitboard::Bitboard;
+use crate::chess::game::Game;
+use crate::chess::movegen::tables;
+use crate::chess::player::Player;
+use crate::engine::eval::params::{
+    ATTACKED_KING_SQUARES, BISHOP_MOBILITY, KNIGHT_MOBILITY, QUEEN_MOBILITY, ROOK_MOBILITY,
+};
+
+fn mobility_and_opp_king_safety_for(game: &Game, player: Player) -> PhasedEval {
+    let mut eval = PhasedEval::ZERO;
+    let blockers = game.board.occupancy();
+
+    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];
+    }
+
+    for p in game.board.bishops(player) {
+        let moves = tables::bishop_attacks(p, blockers);
+        attacked_squares |= moves;
+        eval += BISHOP_MOBILITY[moves.count() as usize];
+    }
+
+    for p in game.board.rooks(player) {
+        let moves = tables::rook_attacks(p, blockers);
+        attacked_squares |= moves;
+        eval += ROOK_MOBILITY[moves.count() as usize];
+    }
+
+    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 enemy_king = game.board.king(player.other()).single();
+    let enemy_king_surrounding_squares = tables::king_attacks(enemy_king);
+    let attacks_on_enemy_king = attacked_squares & enemy_king_surrounding_squares;
+
+    eval -= ATTACKED_KING_SQUARES[attacks_on_enemy_king.count() as usize];
+
+    eval
+}
+
+pub fn eval(game: &Game) -> PhasedEval {
+    mobility_and_opp_king_safety_for(game, Player::White)
+        - mobility_and_opp_king_safety_for(game, Player::Black)
+}

src/engine/eval/mod.rs

@@ -1,5 +1,5 @@
 mod material;
-mod mobility;
+mod mobility_and_king_safety;
 mod params;
 mod phased_eval;
 pub mod piece_square_tables;
@@ -60,7 +60,7 @@ pub fn eval(game: &Game) -> Eval {
 pub fn absolute_eval(game: &Game) -> WhiteEval {
     let eval = game.incremental_eval.piece_square_tables
         + material::eval(game)
-        + mobility::eval(game);
+        + mobility_and_king_safety::eval(game);
 
     eval.for_phase(game.incremental_eval.phase_value)
 }