Add TT cutoffs

src/search/iterative_deepening.rs

@@ -7,10 +7,7 @@ use crate::{
     movegen::r#move::Move,
 };
 
-use super::{
-    negamax,
-    time::TimeInfo,
-};
+use super::{negamax, time::TimeInfo};
 
 pub fn iterative_deepening(
     game: &mut Game,

src/search/mod.rs

@@ -11,4 +11,4 @@ pub const TIME: u128 = 1000;
 pub const INC: u128 = 1000;
 pub const HARD_LIMIT_DIVISION: u128 = 10;
 pub const SOFT_LIMIT_DIVISION: u128 = HARD_LIMIT_DIVISION * 2;
-pub const MAX_TT_SIZE: u64 = 1500000;
+pub const MAX_TT_SIZE: u64 = 750000;

src/search/negamax.rs

@@ -9,7 +9,7 @@ use super::{
     move_ordering::score_move,
     quiescence::quiescence,
     time::TimeInfo,
-    transposition_table::TTEntry,
+    transposition_table::{NodeType, TTEntry},
 };
 
 pub fn negamax(
@@ -30,8 +30,7 @@ pub fn negamax(
     }
 
     if depth == 0 {
-        let q_score =
-            quiescence(game, alpha, beta, time, nodes).map_err(|e| anyhow!("{e}"))?;
+        let q_score = quiescence(game, alpha, beta, time, nodes).map_err(|e| anyhow!("{e}"))?;
         return Ok(q_score);
     }
 
@@ -40,9 +39,22 @@ pub fn negamax(
     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 tt_entry = game.tt.lookup(game.hash);
 
-    moves.sort_unstable_by_key(|mv| score_move(&game.mailbox, *mv, tt_move));
+    if let Some(tt_entry) = tt_entry {
+        if plies > 0 && tt_entry.hash == game.hash && tt_entry.depth >= depth {
+            match tt_entry.node_type {
+                NodeType::Exact => return Ok(tt_entry.score),
+                NodeType::LowerBound if tt_entry.score >= beta => return Ok(tt_entry.score),
+                NodeType::UpperBound if tt_entry.score <= alpha => return Ok(tt_entry.score),
+                _ => (),
+            }
+        }
+    }
+
+    moves.sort_unstable_by_key(|mv| {
+        score_move(&game.mailbox, *mv, tt_entry.and_then(|entry| entry.mv))
+    });
 
     for mv in moves {
         game.make_move(&mv);
@@ -57,15 +69,7 @@ pub fn negamax(
         let score = if legal_moves == 1 {
             -negamax(game, -beta, -alpha, depth - 1, plies + 1, time, nodes)?
         } else {
-            let mut score = -negamax(
-                game,
-                -alpha - 1,
-                -alpha,
-                depth - 1,
-                plies + 1,
-                time,
-                nodes,
-            )?;
+            let mut score = -negamax(game, -alpha - 1, -alpha, depth - 1, plies + 1, time, nodes)?;
             if score > alpha && score < beta {
                 score = -negamax(game, -beta, -alpha, depth - 1, plies + 1, time, nodes)?;
             }
@@ -95,7 +99,15 @@ pub fn negamax(
         return Ok(0);
     }
 
-    game.tt.insert(TTEntry::new(game.hash, best_move));
+    let node_type = match best_score {
+        s if s >= beta => NodeType::LowerBound,
+        s if s <= alpha => NodeType::UpperBound,
+        _ => NodeType::Exact,
+    };
+
+    game.tt.insert(TTEntry::new(
+        game.hash, best_move, depth, best_score, node_type,
+    ));
     Ok(best_score)
 }
 

src/search/quiescence.rs

@@ -2,10 +2,7 @@ use anyhow::{bail, Result};
 
 use crate::{board::game::Game, evaluation::pesto::pesto};
 
-use super::{
-    move_ordering::score_move,
-    time::TimeInfo,
-};
+use super::{move_ordering::score_move, time::TimeInfo, transposition_table::NodeType};
 
 pub fn quiescence(
     game: &mut Game,
@@ -31,9 +28,22 @@ pub fn quiescence(
     let color = game.current_player();
     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);
+    let tt_entry = game.tt.lookup(game.hash);
 
-    moves.sort_unstable_by_key(|mv| score_move(&game.mailbox, *mv, tt_move));
+    if let Some(tt_entry) = tt_entry {
+        if tt_entry.hash == game.hash {
+            match tt_entry.node_type {
+                NodeType::Exact => return Ok(tt_entry.score),
+                NodeType::LowerBound if tt_entry.score >= beta => return Ok(tt_entry.score),
+                NodeType::UpperBound if tt_entry.score <= alpha => return Ok(tt_entry.score),
+                _ => (),
+            }
+        }
+    }
+
+    moves.sort_unstable_by_key(|mv| {
+        score_move(&game.mailbox, *mv, tt_entry.and_then(|entry| entry.mv))
+    });
 
     for mv in moves {
         game.make_move(&mv);

src/search/transposition_table.rs

@@ -15,12 +15,10 @@ impl TranspositionTable {
     }
 
     pub fn lookup(&self, zobrist_hash: ZobristHash) -> Option<&TTEntry> {
-        let entry = self
+        self
             .positions
             .get((zobrist_hash.0 % self.size) as usize)
-            .and_then(|entry| entry.as_ref());
-
-        entry
+            .and_then(|entry| entry.as_ref())
     }
 
     pub fn insert(&mut self, tt_entry: TTEntry) {
@@ -33,13 +31,35 @@ impl TranspositionTable {
 pub struct TTEntry {
     pub hash: ZobristHash,
     pub mv: Option<Move>,
+    pub depth: u8,
+    pub score: i32,
+    pub node_type: NodeType,
 }
 
 impl TTEntry {
-    pub const fn new(hash: ZobristHash, mv: Option<Move>) -> Self {
-        Self { hash, mv }
+    pub const fn new(
+        hash: ZobristHash,
+        mv: Option<Move>,
+        depth: u8,
+        score: i32,
+        node_type: NodeType,
+    ) -> Self {
+        Self {
+            hash,
+            mv,
+            depth,
+            score,
+            node_type,
         }
     }
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub enum NodeType {
+    Exact,
+    LowerBound,
+    UpperBound,
+}
 
 #[cfg(test)]
 mod tests {