Fix and simplify move ordering

src/board/board.rs

@@ -192,17 +192,6 @@ impl PieceType {
     pub const fn idx(self) -> usize {
         self as usize
     }
-
-    pub const fn score(self) -> i32 {
-        match self {
-            Self::Pawn => 100,
-            Self::Knight => 320,
-            Self::Bishop => 330,
-            Self::Rook => 500,
-            Self::Queen => 900,
-            Self::King => 20000,
-        }
-    }
 }
 use std::ops::{Index, IndexMut};
 

src/search/move_ordering.rs

@@ -1,22 +1,14 @@
 use crate::{board::mailbox::Mailbox, movegen::r#move::Move};
 
-pub fn sort_moves(mut moves: Vec<Move>, mailbox: &Mailbox, tt_move: Option<Move>) -> Vec<Move> {
-    if let Some(tt_move) = tt_move {
-        if let Some(tt_move_index) = moves.iter().position(|&mv| mv == tt_move) {
-            moves.swap_remove(tt_move_index);
-            moves.insert(0, tt_move);
-            return moves;
-        }
+pub fn score_move(mailbox: &Mailbox, mv: Move, tt_move: Option<Move>) -> i32 {
+    if Some(mv) == tt_move {
+        return -100;
     }
 
-    moves.sort_unstable_by_key(|mv| std::cmp::Reverse(mvv_lva(mailbox, *mv)));
-    moves
-}
-
-const fn mvv_lva(mailbox: &Mailbox, mv: Move) -> i32 {
-    match (mailbox.piece_at(mv.src), mailbox.piece_at(mv.dst)) {
-        (Some(aggressor), Some(victim)) => victim.0.score() - aggressor.0.score(),
-        _ => -1000,
+    let aggressor = mailbox.piece_at(mv.src).expect("No aggressor found.");
+    match mailbox.piece_at(mv.dst) {
+        Some(victim) => aggressor.0.idx() as i32 - (victim.0.idx() * 8) as i32,
+        None => 100,
     }
 }
 
@@ -25,17 +17,28 @@ mod tests {
     use crate::{
         board::{fen::from_fen, square::Square},
         movegen::r#move::{Move, MoveType},
-        search::move_ordering::mvv_lva,
     };
 
-    const FEN: &'static str = "1r2k2r/2P1pq1p/2npb3/1p3ppP/p3P3/P2B1Q2/1P1PNPP1/R3K2R w KQk g6 0 1";
+    use super::score_move;
+
+    const FEN: &'static str = "1r2k2r/2P1p2p/2npb1q1/1p3ppP/p3P3/P2B1Q2/1P1PNPP1/R3K2R w KQk - 0 1";
 
     #[test]
-    fn test_score_by_mvv_lva() -> Result<(), String> {
+    fn test_score_move() -> Result<(), String> {
         let game = from_fen(FEN)?;
-        let f3f5 = Move::with_type(Square::F3, Square::F5, MoveType::Capture);
+        let queen_takes_pawn = Move::with_type(Square::F3, Square::F5, MoveType::Capture);
+        let pawn_takes_queen = Move::with_type(Square::H5, Square::G6, MoveType::Capture);
+        let castle = Move::with_type(Square::E1, Square::C1, MoveType::Castle);
 
-        assert_eq!(mvv_lva(&game.mailbox, f3f5), -800);
+        let mut moves = vec![castle, queen_takes_pawn, pawn_takes_queen];
+        moves.sort_unstable_by_key(|mv| score_move(&game.mailbox, *mv, None));
+
+        assert_eq!(moves, vec![pawn_takes_queen, queen_takes_pawn, castle]);
+
+        let castle = Move::with_type(Square::E1, Square::C1, MoveType::Castle);
+        moves.sort_unstable_by_key(|mv| score_move(&game.mailbox, *mv, Some(castle)));
+
+        assert_eq!(moves, vec![castle, pawn_takes_queen, queen_takes_pawn]);
 
         Ok(())
     }

src/search/negamax.rs

@@ -6,7 +6,7 @@ use crate::{
 };
 
 use super::{
-    move_ordering,
+    move_ordering::score_move,
     quiescence::quiescence,
     time::{hard_limit, TimeInfo},
     transposition_table::TTEntry,
@@ -33,14 +33,14 @@ pub fn negamax(
         return Ok(q_score);
     }
 
-    let color = game.current_player();
-    let mut best_move = None;
-    let mut best_score = MIN_SCORE;
     let mut legal_moves = 0;
-    let all_moves = game.board.pseudo_moves_all();
-
+    let color = game.current_player();
+    let mut best_score = MIN_SCORE;
+    let mut best_move = None;
+    let mut moves = game.board.pseudo_moves_all();
     let tt_move = game.tt.lookup(game.hash).and_then(|entry| entry.mv);
-    let moves = move_ordering::sort_moves(all_moves, &game.mailbox, tt_move);
+
+    moves.sort_unstable_by_key(|mv| score_move(&game.mailbox, *mv, tt_move));
 
     for mv in moves {
         game.make_move(&mv);

src/search/quiescence.rs

@@ -3,7 +3,7 @@ use anyhow::{bail, Result};
 use crate::{board::game::Game, evaluation::pesto::pesto};
 
 use super::{
-    move_ordering,
+    move_ordering::score_move,
     time::{hard_limit, TimeInfo},
 };
 
@@ -23,10 +23,11 @@ pub fn quiescence(game: &mut Game, mut alpha: i32, beta: i32, time_info: &TimeIn
     }
 
     let color = game.current_player();
-    let all_moves = game.board.pseudo_moves_all_captures();
-    let tt_move = game.tt.lookup(game.hash).and_then(|entry| entry.mv);
-    let moves = move_ordering::sort_moves(all_moves, &game.mailbox, tt_move);
     let mut best_score = stand_pat;
+    let mut moves = game.board.pseudo_moves_all_captures();
+    let tt_move = game.tt.lookup(game.hash).and_then(|entry| entry.mv);
+
+    moves.sort_unstable_by_key(|mv| score_move(&game.mailbox, *mv, tt_move));
 
     for mv in moves {
         game.make_move(&mv);