refactor: separate zobrist module

1 files changed, 79 insertions, 0 deletions

diff --git a/src/board/zobrist.rs b/src/board/zobrist.rs
new file mode 100644
index 0000000..e282074
--- /dev/null
+++ b/src/board/zobrist.rs
@@ -0,0 +1,79 @@
+use rand::{rngs::StdRng,SeedableRng,Rng};
+
+use crate::{square::Square, bitboard::BitboardFns};
+
+use super::{Board, Color, PieceType, CastlingSide};
+
+
+const TOTAL_PIECES:          usize = 12;
+const TOTAL_SQUARES:         usize = 64;
+const TOTAL_FILES:           usize = 8;
+const TOTAL_CASTLING_RIGHTS: usize = 4;
+const ZOBRIST_SEED_SIZE:     usize = TOTAL_SQUARES * TOTAL_PIECES + TOTAL_CASTLING_RIGHTS + TOTAL_FILES + 1;
+
+pub type ZobristSeed = [u64; ZOBRIST_SEED_SIZE];
+
+pub trait Zobrist {
+    fn seed() -> ZobristSeed;
+
+    /// Compute store zobrist hash of the current position
+    /// https://www.chessprogramming.org/Zobrist_Hashing
+    fn compute_hash(&mut self) -> ();
+
+    fn zobrist_toggle_piece(&mut self, piece_type: PieceType, square: Square) -> ();
+    fn zobrist_toggle_castling_right(&mut self, color: Color, side: CastlingSide) -> ();
+    fn zobrist_toggle_ep_square(&mut self, ep_square: Square) -> ();
+    fn zobrist_toggle_color(&mut self) -> ();
+}
+
+impl Zobrist for Board {
+    fn seed() -> ZobristSeed {
+        let mut rng = StdRng::seed_from_u64(228);
+        [(); ZOBRIST_SEED_SIZE].map(|_| rng.gen())
+    }
+
+    fn compute_hash(&mut self) -> () {
+        self.hash = 0;
+
+        for piece_id in 0..self.piece_sets.len() {
+            for square in self.piece_sets[piece_id].serialize() {
+                self.zobrist_toggle_piece(PieceType::from(piece_id), square);
+            }
+        }
+        for color in [Color::White, Color::Black] {
+            for castle_side in [CastlingSide::King, CastlingSide::Queen] {
+                if self.castling_rights[color as usize][castle_side as usize] {
+                    self.zobrist_toggle_castling_right(color, castle_side)
+                }
+            }
+        }
+
+        match self.ep_target {
+            Some(square) => self.zobrist_toggle_ep_square(square),
+            None => {},
+        }
+
+        if self.color() == Color::Black {
+            self.zobrist_toggle_color();
+        }
+    }
+
+    fn zobrist_toggle_piece(&mut self, piece_type: PieceType, square: Square) -> () {
+        self.hash ^= self.zobrist_seed[piece_type as usize * TOTAL_SQUARES + square as usize];
+    }
+
+    fn zobrist_toggle_castling_right(&mut self, color: Color, side: CastlingSide) -> () {
+        self.hash ^= self.zobrist_seed[(TOTAL_PIECES * TOTAL_SQUARES) + color as usize * 2 + side as usize];
+    }
+
+    fn zobrist_toggle_ep_square(&mut self, ep_square: Square) -> () {
+        self.hash ^= self.zobrist_seed[(TOTAL_PIECES * TOTAL_SQUARES + TOTAL_CASTLING_RIGHTS) + ep_square.file() as usize];
+    }
+
+    fn zobrist_toggle_color(&mut self) -> () {
+        self.hash ^= match self.zobrist_seed.last() {
+            Some(x) => x,
+            None => panic!("Something is wrong with zobrist seed list"),
+        };
+    }
+}