Force king cornering via psqt

bdmendes · Apr 21, 2024 · c513baa · c513baa
1 parent 366f0f5
commit c513baa
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Showing 2 changed files with 12 additions and 1 deletion.
diff --git a/src/evaluation/position/mod.rs b/src/evaluation/position/mod.rs
@@ -16,6 +16,12 @@ mod rooks;
 pub const MAX_POSITIONAL_GAIN: ValueScore = 200;
 
 fn midgame_ratio(position: &Position) -> u8 {
+    if position.board.occupancy_bb_all().count_ones() <= 4 {
+        // We are in a "mating" position.
+        // The only goal is to corner the king.
+        return 0;
+    }
+
     Piece::list().iter().fold(0, |acc, piece| {
         acc.saturating_add(
             position.board.pieces_bb(*piece).count_ones() as u8
@@ -68,7 +74,7 @@ impl Evaluable for Position {
         }
 
         let midgame_ratio = midgame_ratio(self);
-        let endgame_ratio = 255 - midgame_ratio;
+        let endgame_ratio = u8::MAX - midgame_ratio;
         let occupancy = self.board.occupancy_bb_all();
 
         let base_score = Piece::list().iter().fold(0, |acc, piece| {

diff --git a/src/evaluation/psqt.rs b/src/evaluation/psqt.rs
@@ -108,6 +108,11 @@ const ENDGAME_PAWN_PSQT: PieceSquareTable = [
 ];
 
 pub fn psqt_value(piece: Piece, square: Square, color: Color, endgame_ratio: u8) -> ValueScore {
+    if endgame_ratio == u8::MAX && matches!(piece, Piece::Queen | Piece::Rook) {
+        // We are in a mating position, so there is no point in evaluating the PSQT.
+        return 0;
+    }
+
     let midgame_psqt = match piece {
         Piece::Pawn => &MIDGAME_PAWN_PSQT,
         Piece::Knight => &MIDGAME_KNIGHT_PSQT,