Refactor keys (#1043)

STC non-reg
Elo   | 0.93 +- 1.72 (95%)
SPRT  | 8.0+0.08s Threads=1 Hash=16MB
LLR   | 3.03 (-2.25, 2.89) [-2.75, 0.25]
Games | N: 39288 W: 10042 L: 9937 D: 19309
Penta | [140, 4309, 10663, 4370, 162]
https://recklesschess.space/test/14978/

Bench: 3466720 

Co-Authored-By: Adarsh Das <adarshdas950@gmail.com>

Author: 87flowers

src/board.rs

@@ -5,8 +5,8 @@ use crate::{
     },
     setwise::{bishop_attacks_setwise, knight_attacks_setwise, pawn_attacks_setwise, rook_attacks_setwise},
     types::{
-        Bitboard, Castling, CastlingKind, Color, File, Move, PAWN_HOME_RANK, PROMO_RANK, Piece, PieceType, Square,
-        ZOBRIST,
+        Bitboard, Castling, CastlingKind, Color, File, Keys, Move, PAWN_HOME_RANK, PROMO_RANK, Piece, PieceType,
+        Square, ZOBRIST,
     },
 };
 
@@ -24,9 +24,7 @@ mod see;
 /// Implements the `Copy` trait for efficient memory duplication via bitwise copying.
 #[derive(Copy, Clone, Default)]
 struct InternalState {
-    key: u64,
-    pawn_key: u64,
-    non_pawn_keys: [u64; Color::NUM],
+    keys: Keys,
     en_passant: Square,
     castling: Castling,
     halfmove_clock: u8,
@@ -83,15 +81,15 @@ impl Board {
         // To mitigate Graph History Interaction (GHI) problems, the hash key is changed
         // every 8 plies to distinguish between positions that would otherwise appear
         // identical to the transposition table.
-        self.state.key ^ ZOBRIST.halfmove_clock[self.halfmove_clock_bucket()]
+        self.state.keys.full() ^ ZOBRIST.halfmove_clock[self.halfmove_clock_bucket()]
     }
 
     pub const fn pawn_key(&self) -> u64 {
-        self.state.pawn_key
+        self.state.keys.pawn()
     }
 
     pub const fn non_pawn_key(&self, color: Color) -> u64 {
-        self.state.non_pawn_keys[color as usize]
+        self.state.keys.non_pawn(color)
     }
 
     pub const fn pinned(&self, color: Color) -> Bitboard {
@@ -222,15 +220,7 @@ impl Board {
     }
 
     pub fn update_hash(&mut self, piece: Piece, square: Square) {
-        let key = ZOBRIST.pieces[piece][square];
-
-        self.state.key ^= key;
-
-        if piece.piece_type() == PieceType::Pawn {
-            self.state.pawn_key ^= key;
-        } else {
-            self.state.non_pawn_keys[piece.color()] ^= key;
-        }
+        self.state.keys.toggle(piece, square);
     }
 
     /// Checks for a material draw
@@ -293,23 +283,23 @@ impl Board {
             return false;
         }
 
-        let current_key = self.state.key;
+        let current_key = self.state.keys.full();
         let stack = &self.state_stack;
         let len = stack.len();
 
         let mut index = len - 1;
-        let mut other = current_key ^ stack[index].key ^ ZOBRIST.side;
+        let mut other = current_key ^ stack[index].keys.full() ^ ZOBRIST.side;
 
         for compared_ply in (3..=half_moves).step_by(2) {
             index -= 1;
-            other ^= stack[index].key ^ stack[index - 1].key ^ ZOBRIST.side;
+            other ^= stack[index].keys.full() ^ stack[index - 1].keys.full() ^ ZOBRIST.side;
             index -= 1;
 
             if other != 0 {
                 continue;
             }
 
-            let diff = current_key ^ stack[index].key;
+            let diff = current_key ^ stack[index].keys.full();
             let mut cuckoo_index = h1(diff);
 
             if cuckoo(cuckoo_index) != diff {
@@ -493,9 +483,7 @@ impl Board {
     }
 
     pub fn update_hash_keys(&mut self) {
-        self.state.key = 0;
-        self.state.pawn_key = 0;
-        self.state.non_pawn_keys = [0; Color::NUM];
+        self.state.keys = Keys::default();
 
         for piece in 0..Piece::NUM {
             let piece = Piece::from_index(piece);
@@ -506,14 +494,14 @@ impl Board {
         }
 
         if self.en_passant() != Square::None {
-            self.state.key ^= ZOBRIST.en_passant[self.en_passant()];
+            self.state.keys.toggle_en_passant(self.en_passant());
         }
 
         if self.side_to_move() == Color::White {
-            self.state.key ^= ZOBRIST.side;
+            self.state.keys.toggle_side();
         }
 
-        self.state.key ^= ZOBRIST.castling[self.state.castling];
+        self.state.keys.toggle_castling(self.state.castling);
     }
 
     fn is_en_passant_valid(&self) -> bool {
@@ -546,7 +534,7 @@ impl Board {
             return;
         }
 
-        self.state.key ^= ZOBRIST.en_passant[self.en_passant()];
+        self.state.keys.toggle_en_passant(self.en_passant());
         self.state.en_passant = Square::None;
     }
 

src/board/makemove.rs

@@ -1,20 +1,21 @@
 use super::{Board, BoardObserver};
-use crate::types::{Move, MoveKind, Piece, PieceType, Square, ZOBRIST};
+use crate::types::{Move, MoveKind, Piece, PieceType, Square};
 
 impl Board {
     pub fn make_null_move(&mut self) {
         self.side_to_move = !self.side_to_move;
         self.state_stack.push(self.state);
 
-        self.state.key ^= ZOBRIST.side ^ ZOBRIST.castling[self.state.castling];
+        self.state.keys.toggle_side();
+        self.state.keys.toggle_castling(self.state.castling);
         self.state.plies_from_null = 0;
         self.state.repetition = 0;
         self.state.captured = None;
 
         self.update_threats();
 
         if self.en_passant() != Square::None {
-            self.state.key ^= ZOBRIST.en_passant[self.en_passant()];
+            self.state.keys.toggle_en_passant(self.en_passant());
             self.state.en_passant = Square::None;
         }
     }
@@ -35,10 +36,11 @@ impl Board {
 
         self.state_stack.push(self.state);
 
-        self.state.key ^= ZOBRIST.castling[self.state.castling] ^ ZOBRIST.side;
+        self.state.keys.toggle_side();
+        self.state.keys.toggle_castling(self.state.castling);
 
         if self.en_passant() != Square::None {
-            self.state.key ^= ZOBRIST.en_passant[self.en_passant()];
+            self.state.keys.toggle_en_passant(self.en_passant());
             self.state.en_passant = Square::None;
         }
 
@@ -90,7 +92,7 @@ impl Board {
         match mv.kind() {
             MoveKind::DoublePush => {
                 self.state.en_passant = to ^ 8;
-                self.state.key ^= ZOBRIST.en_passant[self.en_passant()];
+                self.state.keys.toggle_en_passant(self.en_passant());
             }
             MoveKind::EnPassant => {
                 let captured = self.remove_piece(to ^ 8);
@@ -120,7 +122,7 @@ impl Board {
         self.side_to_move = !self.side_to_move;
 
         self.state.castling.raw &= self.castling_rights[from] & self.castling_rights[to];
-        self.state.key ^= ZOBRIST.castling[self.state.castling];
+        self.state.keys.toggle_castling(self.state.castling);
 
         self.update_threats();
         self.update_en_passant();
@@ -138,7 +140,7 @@ impl Board {
 
                 let stp = &self.state_stack[idx as usize];
 
-                if stp.key == self.state.key {
+                if stp.keys.full() == self.state.keys.full() {
                     self.state.repetition = if stp.repetition != 0 { -(i as i32) } else { i as i32 };
                     break;
                 }

src/types/keys.rs

@@ -0,0 +1,45 @@
+use crate::types::{Castling, Color, Piece, PieceType, Square, ZOBRIST};
+
+#[derive(Clone, Copy, Default)]
+pub struct Keys {
+    pub full: u64,
+    pub pawn: u64,
+    pub non_pawn: [u64; Color::NUM],
+}
+
+impl Keys {
+    pub fn full(&self) -> u64 {
+        self.full
+    }
+
+    pub const fn pawn(&self) -> u64 {
+        self.pawn
+    }
+
+    pub const fn non_pawn(&self, color: Color) -> u64 {
+        self.non_pawn[color as usize]
+    }
+
+    pub fn toggle(&mut self, piece: Piece, sq: Square) {
+        let piece_key = ZOBRIST.pieces[piece][sq];
+
+        self.full ^= piece_key;
+
+        match piece.piece_type() {
+            PieceType::Pawn => self.pawn ^= piece_key,
+            _ => self.non_pawn[piece.color()] ^= piece_key,
+        }
+    }
+
+    pub fn toggle_side(&mut self) {
+        self.full ^= ZOBRIST.side;
+    }
+
+    pub fn toggle_castling(&mut self, castling: Castling) {
+        self.full ^= ZOBRIST.castling[castling];
+    }
+
+    pub fn toggle_en_passant(&mut self, en_passant: Square) {
+        self.full ^= ZOBRIST.en_passant[en_passant];
+    }
+}

src/types/mod.rs

@@ -2,6 +2,7 @@ pub mod arrayvec;
 pub mod bitboard;
 pub mod castling;
 pub mod color;
+pub mod keys;
 pub mod movelist;
 pub mod moves;
 pub mod piece;
@@ -13,6 +14,7 @@ pub use arrayvec::*;
 pub use bitboard::*;
 pub use castling::*;
 pub use color::*;
+pub use keys::*;
 pub use movelist::*;
 pub use moves::*;
 pub use piece::*;