Simplify move hashing (#1064)

STC
Elo   | 1.09 +- 1.89 (95%)
SPRT  | 8.0+0.08s Threads=1 Hash=16MB
LLR   | 2.94 (-2.25, 2.89) [-2.75, 0.25]
Games | N: 35534 W: 9127 L: 9016 D: 17391
Penta | [193, 4015, 9245, 4116, 198]
https://recklesschess.space/test/15171/

No functional change.

Bench: 3634130

Author: protonspring

src/board.rs

@@ -200,13 +200,15 @@ impl Board {
         self.mailbox[square] = piece;
         self.colors[piece.color()].set(square);
         self.pieces[piece.piece_type()].set(square);
+        self.update_hash(piece, square);
     }
 
     pub fn remove_piece(&mut self, square: Square) -> Piece {
         let piece = self.mailbox[square];
         self.mailbox[square] = Piece::None;
         self.colors[piece.color()].clear(square);
         self.pieces[piece.piece_type()].clear(square);
+        self.update_hash(piece, square);
         piece
     }
 

src/board/makemove.rs

@@ -59,9 +59,6 @@ impl Board {
 
             self.add_piece(rook, rook_to);
             observer.on_piece_change(self, rook, rook_to, true);
-
-            self.update_hash(rook, rook_from);
-            self.update_hash(rook, rook_to);
         } else if captured != Piece::None {
             self.remove_piece(from);
             observer.on_piece_change(self, piece, from, false);
@@ -70,8 +67,6 @@ impl Board {
             self.add_piece(piece, to);
             observer.on_piece_mutate(self, captured, piece, to);
 
-            self.update_hash(captured, to);
-
             self.state.material -= captured.value();
             self.state.captured = Some(captured);
         } else {
@@ -82,7 +77,6 @@ impl Board {
             if mv.is_en_passant() {
                 let captured = self.remove_piece(to ^ 8);
                 observer.on_piece_change(self, captured, to ^ 8, false);
-                self.update_hash(captured, to ^ 8);
                 self.state.material -= captured.value();
                 self.state.captured = Some(captured);
             } else if mv.is_double_push() {
@@ -91,19 +85,13 @@ impl Board {
             }
         }
 
-        self.update_hash(piece, from);
-        self.update_hash(piece, to);
-
         if mv.is_promotion() {
             let promotion = Piece::new(stm, mv.promo_piece_type());
 
             self.remove_piece(to);
             self.add_piece(promotion, to);
             observer.on_piece_mutate(self, piece, promotion, to);
 
-            self.update_hash(piece, to);
-            self.update_hash(promotion, to);
-
             self.state.material += promotion.value() - PieceType::Pawn.value();
         }