-
Notifications
You must be signed in to change notification settings - Fork 0
Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
- Loading branch information
Showing
3 changed files
with
111 additions
and
84 deletions.
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,83 @@ | ||
| use super::{constraint::SearchConstraint, movepick::MovePicker, see, Depth}; | ||
| use crate::{ | ||
| evaluation::{position::MAX_POSITIONAL_GAIN, Evaluable, ValueScore, MATE_SCORE}, | ||
| position::{board::Piece, Position}, | ||
| }; | ||
|
|
||
| pub fn quiesce( | ||
| position: &Position, | ||
| mut alpha: ValueScore, | ||
| beta: ValueScore, | ||
| constraint: &SearchConstraint, | ||
| ply: Depth, | ||
| ) -> (ValueScore, usize) { | ||
| // Time limit reached | ||
| if constraint.should_stop_search() { | ||
| return (alpha, 1); | ||
| } | ||
|
|
||
| // If we are in check, the position is certainly not quiet, | ||
| // so we must search all check evasions. Otherwise, search only captures | ||
| let is_check = position.is_check(); | ||
| let static_evaluation = if is_check { | ||
| alpha | ||
| } else { | ||
| let static_evaluation = position.value() * position.side_to_move.sign(); | ||
|
|
||
| // Standing pat: captures are not forced | ||
| alpha = alpha.max(static_evaluation); | ||
|
|
||
| // Beta cutoff: position is too good | ||
| if static_evaluation >= beta { | ||
| return (beta, 1); | ||
| } | ||
|
|
||
| // Delta pruning: sequence cannot improve the score | ||
| if static_evaluation < alpha.saturating_sub(Piece::Queen.value()) { | ||
| return (alpha, 1); | ||
| } | ||
|
|
||
| static_evaluation | ||
| }; | ||
|
|
||
| let mut picker = MovePicker::<true>::new(position, is_check).peekable(); | ||
|
|
||
| // Stable position reached | ||
| if picker.peek().is_none() { | ||
| let score = if is_check { MATE_SCORE + ply as ValueScore } else { static_evaluation }; | ||
| return (score, 1); | ||
| } | ||
|
|
||
| let mut count = 1; | ||
|
|
||
| for (mov, _) in picker { | ||
| if !is_check && mov.flag().is_capture() { | ||
| // Delta pruning: this capture cannot improve the score in any way. | ||
| let captured_piece = | ||
| position.board.piece_color_at(mov.to()).map_or_else(|| Piece::Pawn, |p| p.0); | ||
| if static_evaluation + captured_piece.value() + MAX_POSITIONAL_GAIN < alpha { | ||
| continue; | ||
| } | ||
|
|
||
| // Static exchange evaluation: if we lose material, there is no point in searching further. | ||
| if see::see::<true>(mov, &position.board) < 0 { | ||
| continue; | ||
| } | ||
| } | ||
|
|
||
| let (score, nodes) = | ||
| quiesce(&position.make_move(mov), -beta, -alpha, constraint, ply.saturating_add(1)); | ||
| let score = -score; | ||
| count += nodes; | ||
|
|
||
| if score > alpha { | ||
| alpha = score; | ||
|
|
||
| if score >= beta { | ||
| break; | ||
| } | ||
| } | ||
| } | ||
|
|
||
| (alpha, count) | ||
| } |