diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/board/engine.rs | 25 |
1 files changed, 21 insertions, 4 deletions
diff --git a/src/board/engine.rs b/src/board/engine.rs index a5f6894..c43a722 100644 --- a/src/board/engine.rs +++ b/src/board/engine.rs @@ -250,8 +250,8 @@ impl Board { let mut ordered_moves: Vec<Move> = moves_with_eval.iter().map(|(m, _)| *m).collect(); - // Insert killer moves after non-losing captures - let losing_capture_index = match moves_with_eval.iter().position(|(m, eval)| m.is_tactical() && *eval < 0.0) { + // Insert killer moves after winning captures + let equal_capture_index = match moves_with_eval.iter().position(|(m, eval)| m.is_tactical() && *eval == 0.0) { Some(x) => x, None => 0, }; @@ -260,7 +260,7 @@ impl Board { match ordered_moves.iter().position(|m| *m == killer) { Some(index) => { let mov = ordered_moves.remove(index); - ordered_moves.insert(losing_capture_index, mov); + ordered_moves.insert(equal_capture_index, mov); } None => {} }; @@ -287,6 +287,7 @@ impl Board { return (self.quiscence(alpha, beta), principal_variation); } + let mut should_pv_search = true; let mut legal_move_found = false; for mov in moves { let ep_target_before = self.ep_target.clone(); @@ -296,7 +297,22 @@ impl Board { if !self.is_king_in_check(color) { legal_move_found = true; - let (mut score, mut subtree_pv) = self.negamax_search(-beta, -alpha, depth_left - 1, &mut killer_moves, deadline); + + let (mut score, mut subtree_pv) = if should_pv_search { + // Assume PV-node is high in the list (if move ordering is good) + self.negamax_search(-beta, -alpha, depth_left - 1, &mut killer_moves, deadline) + } else { + // After we have PV-node (that raised alpha) all other nodes will be searched + // with zero-window first to confirm this assumption + let result = self.negamax_search(-(alpha + 0.0001), -alpha, depth_left - 1, &mut killer_moves, deadline); + // In case some of the other nodes raises alpha, then it's true PV node now, + // let's research with full window to find its exact value + if -result.0 > alpha { + self.negamax_search(-beta, -alpha, depth_left - 1, &mut killer_moves, deadline) + } else { + result + } + }; score *= -1.; self.unmake_move(mov, captured_piece, ep_target_before, castling_rights_before, hash_before); @@ -320,6 +336,7 @@ impl Board { } if score > alpha { alpha = score; + should_pv_search = false; // Once we have PV-node we can start zero-window searching principal_variation = Vec::with_capacity(depth_left as usize); principal_variation.push(mov); principal_variation.append(&mut subtree_pv); |