add square attackers fct

src/attack.c

@@ -0,0 +1,67 @@
+/* attack.c - attack functions.
+ *
+ * Copyright (C) 2024 Bruno Raoult ("br")
+ * Licensed under the GNU General Public License v3.0 or later.
+ * Some rights reserved. See COPYING.
+ *
+ * You should have received a copy of the GNU General Public License along with this
+ * program. If not, see <https://www.gnu.org/licenses/gpl-3.0-standalone.html>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later <https://spdx.org/licenses/GPL-3.0-or-later.html>
+ *
+ */
+
+#include <stdio.h>
+#include <stdarg.h>
+
+#include "chessdefs.h"
+#include "bitboard.h"
+#include "position.h"
+#include "hyperbola-quintessence.h"
+
+/**
+ * square_attackers() - find attackers on a square
+ * @pos: position
+ * @sq:  square to test
+ * @c:   attacker color
+ *
+ * Find all @c attacks on @sq. En-passant is not considered.
+ *
+ * Algorithm:  We perform a reverse attack, and check if any given
+ * piece type on @sq can attack a @c piece of same type.
+ *
+ * For example, if @c is white, we test for all T in P,N,B,R,Q,K if
+ * T on @sq could attack a white T piece.
+ *
+ * @Return: a bitboard of attackers.
+ *
+ */
+bitboard_t sq_attackers(pos_t *pos, square_t sq, color_t c)
+{
+    bitboard_t attackers = 0;
+    bitboard_t from = mask(sq);
+    bitboard_t c_pieces = pos->bb[c][ALL_PIECES];
+    bitboard_t occ = c_pieces | pos->bb[OPPONENT(c)][ALL_PIECES];
+    bitboard_t to;
+
+    /* pawn */
+    to =  pos->bb[c][PAWN];
+    attackers |= pawn_push_upleft(from, c) & to;
+    attackers |= pawn_push_upright(from, c) & to;
+
+    /* knight & king */
+    to = pos->bb[c][KNIGHT];
+    attackers |= bb_knight_moves(c_pieces, from);
+    to = pos->bb[c][KING];
+    attackers |= bb_king_moves(c_pieces, from);
+
+    /* bishop / queen */
+    to = pos->bb[c][BISHOP] | pos->bb[c][QUEEN];
+    attackers |= hyperbola_bishop_moves(occ, from) & to;
+
+    /* rook / queen */
+    to = pos->bb[c][ROOK] | pos->bb[c][QUEEN];
+    attackers |= hyperbola_rook_moves(occ, from) & to;
+
+    return attackers;
+}

src/attack.h

@@ -0,0 +1,22 @@
+/* attack.h - attack functions.
+ *
+ * Copyright (C) 2024 Bruno Raoult ("br")
+ * Licensed under the GNU General Public License v3.0 or later.
+ * Some rights reserved. See COPYING.
+ *
+ * You should have received a copy of the GNU General Public License along with this
+ * program. If not, see <https://www.gnu.org/licenses/gpl-3.0-standalone.html>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later <https://spdx.org/licenses/GPL-3.0-or-later.html>
+ *
+ */
+
+#ifndef _ATTACK_H
+#define _ATTACK_H
+
+#include "chessdefs.h"
+#include "bitboard.h"
+
+extern bitboard_t sq_attackers(pos_t *pos, square_t sq, color_t c);
+
+#endif