Add history heuristics, reorder killer move to come after captures

src/board/fen.rs

@@ -38,6 +38,7 @@ pub fn from_fen(fen: &str) -> Result<Game, FenError> {
         hash,
         tt: TranspositionTable::new(),
         killer: [None; MAX_DEPTH as usize],
+        history_heuristic: [[[0; 64]; 64]; 2],
     })
 }
 

src/board/game.rs

@@ -30,6 +30,7 @@ pub struct Game {
     pub hash: ZobristHash,
     pub tt: TranspositionTable,
     pub killer: [Option<Move>; MAX_DEPTH as usize],
+    pub history_heuristic: [[[i16; 64]; 64]; 2],
 }
 
 impl Game {
@@ -41,6 +42,7 @@ impl Game {
             hash: zobrist_keys().calculate_hash(&Board::startpos()),
             tt: TranspositionTable::new(),
             killer: [None; MAX_DEPTH as usize],
+            history_heuristic: [[[0; 64]; 64]; 2],
         }
     }
 

src/search/mod.rs

@@ -12,3 +12,4 @@ pub const INC: u128 = 80;
 pub const HARD_LIMIT_DIVISION: u128 = 3;
 pub const SOFT_LIMIT_DIVISION: u128 = 20;
 pub const TT_SIZE_IN_MB: usize = 64;
+pub const MAX_HISTORY: i16 = 8192;

src/search/move_ordering.rs

@@ -1,25 +1,36 @@
-use crate::{board::mailbox::Mailbox, movegen::r#move::Move};
+use crate::{
+    board::{board::Color, mailbox::Mailbox},
+    movegen::r#move::Move,
+};
 
+use super::MAX_HISTORY;
+
+// ttmove: -100, mvvlva: [-32, 5], killer:6, quiet[7, ..]
 pub fn score_move(
     mailbox: &Mailbox,
     mv: Move,
     killer_move: Option<Move>,
+    color: Color,
+    history_heuristic: &[[[i16; 64]; 64]; 2],
     tt_move: Option<Move>,
 ) -> i16 {
     if Some(mv) == tt_move {
         return -100;
     }
 
+    if mv.is_capture() {
+        let aggressor = mailbox.piece_at(mv.src()).unwrap();
+        if let Some(victim) = mailbox.piece_at(mv.dst()) {
+            return aggressor.0.idx() as i16 - 8 * victim.0.idx() as i16;
+        }
+        return 0; //en passant
+    }
+
     if Some(mv) == killer_move {
-        return -90;
+        return 6;
     }
 
-    let aggressor = mailbox.piece_at(mv.src()).expect("No aggressor found.");
-    if let Some(victim) = mailbox.piece_at(mv.dst()) {
-        return (aggressor.0.idx() - 8 * victim.0.idx()) as i16;
-    }
-
-    100
+    -history_heuristic[color][mv.src()][mv.dst()] + MAX_HISTORY + 6 + 1
 }
 
 #[cfg(test)]
@@ -41,11 +52,29 @@ mod tests {
         let castle = Move::new_with_type(Square::E1, Square::C1, MoveType::QueenCastle);
 
         let mut moves = vec![castle, queen_takes_pawn, pawn_takes_queen];
-        moves.sort_unstable_by_key(|mv| score_move(&game.mailbox, *mv, None, None));
+        moves.sort_unstable_by_key(|mv| {
+            score_move(
+                &game.mailbox,
+                *mv,
+                None,
+                game.current_player(),
+                &[[[0; 64]; 64]; 2],
+                None,
+            )
+        });
 
         assert_eq!(moves, vec![pawn_takes_queen, queen_takes_pawn, castle]);
 
-        moves.sort_unstable_by_key(|mv| score_move(&game.mailbox, *mv, None, Some(castle)));
+        moves.sort_unstable_by_key(|mv| {
+            score_move(
+                &game.mailbox,
+                *mv,
+                None,
+                game.current_player(),
+                &[[[0; 64]; 64]; 2],
+                Some(castle),
+            )
+        });
 
         assert_eq!(moves, vec![castle, pawn_takes_queen, queen_takes_pawn]);
 

src/search/negamax.rs

@@ -10,6 +10,7 @@ use super::{
     quiescence::quiescence,
     time::TimeInfo,
     transposition_table::{NodeType, TTEntry},
+    MAX_HISTORY,
 };
 
 pub fn negamax(
@@ -78,6 +79,8 @@ pub fn negamax(
             &game.mailbox,
             *mv,
             game.killer[plies as usize],
+            color,
+            &game.history_heuristic,
             entry.and_then(|entry| entry.mv),
         )
     });
@@ -129,8 +132,16 @@ pub fn negamax(
         if score >= beta {
             if !mv.is_capture() {
                 game.killer[plies as usize] = Some(mv);
+
+                let current_score = game.history_heuristic[color][mv.src()][mv.dst()];
+                let bonus = (depth * depth) as i16;
+                let clamped_bonus = bonus.clamp(-MAX_HISTORY, MAX_HISTORY);
+                game.history_heuristic[color][mv.src()][mv.dst()] +=
+                    clamped_bonus - current_score * clamped_bonus.abs() / MAX_HISTORY;
             }
             break;
+        } else if !mv.is_capture() {
+            game.history_heuristic[color][mv.src()][mv.dst()] -= 1;
         }
     }
 

src/search/quiescence.rs

@@ -38,7 +38,14 @@ pub fn quiescence(
     let mut moves = game.board.pseudo_moves_all_captures();
 
     moves.sort_unstable_by_key(|mv| {
-        score_move(&game.mailbox, *mv, None, entry.and_then(|entry| entry.mv))
+        score_move(
+            &game.mailbox,
+            *mv,
+            None,
+            color,
+            &[[[0; 64]; 64]; 2],
+            entry.and_then(|entry| entry.mv),
+        )
     });
 
     for mv in moves {