added methods for detecting pinned pieces

engine/src/bitboard/legality.rs

@@ -0,0 +1,48 @@
+use super::board::Board;
+use super::attackmaps::RAY_TABLE;
+
+impl Board {
+
+  pub(in super) fn calc_pinned_squares(&mut self) {
+    self.pinned_squares = [4; 64];
+    self.pin_mask = 0u64;
+
+    let friendly_pieces: u64 = self.occupancy[self.side_to_move as usize];
+    let offset: usize = 6 * self.side_to_move as usize;
+    let king_board: u64 = self.bitboards[5 + offset];
+    let king_sq: u32 = king_board.trailing_zeros();
+    let opponent_queen_bishop_mask: u64 = self.bitboards[8 - offset] | self.bitboards[10 - offset];
+    let opponent_queen_rook_mask: u64 = self.bitboards[9 - offset] | self.bitboards[10 - offset];
+
+    // Queen-Rook directions
+    self.set_pinned_in_ray_direction(king_sq, friendly_pieces, opponent_queen_rook_mask, 0);
+    self.set_pinned_in_ray_direction(king_sq, friendly_pieces, opponent_queen_rook_mask, 2);
+    self.set_pinned_in_ray_direction(king_sq, friendly_pieces, opponent_queen_rook_mask, 4);
+    self.set_pinned_in_ray_direction(king_sq, friendly_pieces, opponent_queen_rook_mask, 6);
+
+    // Queen-Bishop directions
+    self.set_pinned_in_ray_direction(king_sq, friendly_pieces, opponent_queen_bishop_mask, 1);
+    self.set_pinned_in_ray_direction(king_sq, friendly_pieces, opponent_queen_bishop_mask, 3);
+    self.set_pinned_in_ray_direction(king_sq, friendly_pieces, opponent_queen_bishop_mask, 5);
+    self.set_pinned_in_ray_direction(king_sq, friendly_pieces, opponent_queen_bishop_mask, 7);
+  }
+
+  pub(in super) fn set_pinned_in_ray_direction(&mut self, king_sq: u32, friendly_pieces: u64, attackers: u64, dir: u8) {
+    let is_up: bool = dir / 4 == 0;
+    let mask: u64 = RAY_TABLE[king_sq as usize][dir as usize];
+    let blockers: u64 = self.occupancy[2] & mask;
+    if blockers == 0 { return; }
+    let first_blocker_sq: u32 = if is_up { blockers.trailing_zeros() } else { 63 - blockers.leading_zeros() };
+    if (friendly_pieces & 1 << first_blocker_sq) != 0 {
+      let blockers: u64 = blockers & !(1 << first_blocker_sq);
+      if blockers == 0 { return; }
+      let second_blocker_sq: u32 = if is_up { blockers.trailing_zeros() } else { 63 - blockers.leading_zeros() };
+
+      if (attackers & 1 << second_blocker_sq) != 0 {
+        self.pinned_squares[first_blocker_sq as usize] = dir % 4;
+        self.pin_mask |= 1 << first_blocker_sq;
+      }
+    }
+  }
+
+}