Return early if king is under check and small refactorings

src/evaluation/evaluation.rs

@@ -6,9 +6,6 @@ use crate::{
     evaluation::psqt::{mirror_index, piece_square_score},
 };
 
-pub const MAX_EVAL: i32 = 100000;
-pub const MIN_EVAL: i32 = -100000;
-
 const fn piece_score(piece_type: PieceType) -> i32 {
     match piece_type {
         PieceType::Pawn => 100,

src/evaluation/mod.rs

@@ -1,2 +1,6 @@
 pub mod evaluation;
 pub mod psqt;
+
+pub const MAX_SCORE: i32 = 100000;
+pub const MIN_SCORE: i32 = -100000;
+pub const MATE_SCORE: i32 = 50000;

src/interface/uci.rs

@@ -5,7 +5,7 @@ use std::{
 
 use crate::{
     board::game::Game,
-    evaluation::evaluation::{MAX_EVAL, MIN_EVAL},
+    evaluation::{MAX_SCORE, MIN_SCORE},
     movegen::r#move::Move,
     search,
 };
@@ -139,8 +139,8 @@ pub fn uci_go(go: &mut SplitWhitespace, game: &mut Game) -> Result<Move, String>
     }
     Ok(search::negamax::negamax(
         game,
-        MIN_EVAL,
-        MAX_EVAL,
+        MIN_SCORE,
+        MAX_SCORE,
         params.depth.unwrap_or(MAX_DEPTH),
         0,
     )

src/search/negamax.rs

@@ -1,6 +1,6 @@
 use crate::{
     board::{game::Game, history::MoveParameters},
-    evaluation::evaluation::evaluate_position,
+    evaluation::{MATE_SCORE, MIN_SCORE},
     movegen::r#move::Move,
 };
 
@@ -19,32 +19,32 @@ pub fn negamax(
         return (None, quiescence(game, alpha, beta).1);
     }
 
-    let (mut best_move, mut best_score, mate_score) = (None, -100000, -50000 + plies as i32);
+    let (mut best_move, mut best_score, mate_score) = (None, MIN_SCORE, -MATE_SCORE + plies as i32);
     let mut legal_moves = 0;
 
     for mv in game.board.pseudo_moves_all(color) {
         let move_parameters = MoveParameters::build(&game.board, &mv);
         game.board.make_move(&mv);
 
-        if !game.board.king_under_check(color) {
-            legal_moves += 1;
-            let move_score = -negamax(game, -beta, -alpha, depth - 1, plies + 1).1;
-
-            if move_score > best_score {
-                best_score = move_score;
-                best_move = Some(mv)
-            }
-
-            if move_score >= beta {
-                game.board.unmake_move(move_parameters);
-                return (Some(mv), beta); // fail hard beta-cutoff
-            }
-
-            if move_score > alpha {
-                alpha = move_score; // alpha acts like max in minimax
-            }
+        if game.board.king_under_check(color) {
+            game.board.unmake_move(move_parameters);
+            continue;
         }
+
+        legal_moves += 1;
+        let move_score = -negamax(game, -beta, -alpha, depth - 1, plies + 1).1;
         game.board.unmake_move(move_parameters);
+
+        if move_score > best_score {
+            best_score = move_score;
+            best_move = Some(mv)
+        }
+
+        if move_score >= beta {
+            return (Some(mv), beta);
+        }
+
+        alpha = alpha.max(move_score);
     }
 
     if legal_moves == 0 {
@@ -60,7 +60,7 @@ pub fn negamax(
 #[cfg(test)]
 mod tests {
     use crate::board::{fen::from_fen, square::Square};
-    use crate::evaluation::evaluation::{MAX_EVAL, MIN_EVAL};
+    use crate::evaluation::{MAX_SCORE, MIN_SCORE};
     use crate::movegen::attack::init_attacks;
     use crate::movegen::r#move::Move;
     use crate::search::negamax::negamax;
@@ -73,23 +73,9 @@ mod tests {
         let mut game = from_fen(FEN_MATE_IN_1)?;
 
         let e3f2 = Move::new(Square::E3, Square::F2);
+        let anointed_move = negamax(&mut game, MIN_SCORE, MAX_SCORE, 2, 0).0.unwrap();
 
-        assert_eq!(
-            e3f2,
-            negamax(&mut game, MIN_EVAL, MAX_EVAL, 2, 0).0.unwrap()
-        );
-        assert_eq!(
-            e3f2,
-            negamax(&mut game, MIN_EVAL, MAX_EVAL, 3, 0).0.unwrap()
-        );
-        assert_eq!(
-            e3f2,
-            negamax(&mut game, MIN_EVAL, MAX_EVAL, 4, 0).0.unwrap()
-        );
-        assert_eq!(
-            e3f2,
-            negamax(&mut game, MIN_EVAL, MAX_EVAL, 5, 0).0.unwrap()
-        );
+        assert_eq!(e3f2, anointed_move);
 
         Ok(())
     }