engine/src/bitboard.c

@@ -785,6 +785,26 @@ int get_legal_moves(struct Board *board, struct Move *out) {
     return count;
 }
 
+uint64_t perft(struct Board *board, int depth) {
+    if (depth == 0) return 1;
+
+    struct Move moves[256];
+    int n = get_legal_moves(board, moves);
+
+    if (depth == 1) return (uint64_t) n;
+    
+    uint64_t nodes = 0;
+    for (int i = 0; i < n; ++i) {
+        struct Board after;
+        if (!apply_move_on_copy(board, &after, moves[i])) {
+            // Shouldn't happen with legal moves, but be defensive
+            continue;
+        }
+        nodes += perft(&after, depth - 1);
+    }
+    return nodes;
+}
+
 void print_board(const struct Board *board) {
     const char PIECE_CH[12] = {
         'P','N','B','R','Q','K',

test/chess_ffi.py

@@ -98,6 +98,8 @@ in_check = _bind_opt("in_check", INCHECK_ARGS, C.c_bool)
 attackers_to = _bind_opt("attackers_to", ATTACKERS_TO, C.c_uint64)
 get_legal_moves = _bind_opt("get_legal_moves", GEN_LEGAL_MOVES, C.c_int)
 
+PERFT_SIG = (C.POINTER(Board), C.c_int)
+perft = _bind_opt("perft", PERFT_SIG, C.c_uint64)
 
 # Attack cache tables.
 KnightArr = (C.c_uint64 * 64)

test/test_perft.py

@@ -0,0 +1,33 @@
+from test.base import ChessLibTestBase
+from test.chess_ffi import Board, perft
+
+
+class TestPerft(ChessLibTestBase):
+    def test_start_position(self):
+        b = Board()
+        self.load_fen("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1", board=b)
+        expected = {
+            1: 20,
+            2: 400,
+            3: 8902,
+            #4: 197281,
+            # 5: 4865609,
+            # 6: 119060324
+        }
+        for d, want in expected.items():
+            got = int(perft(b, d))
+            self.assertEqual(got, want, f"perft({d}) start pos")
+
+    """
+    def test_kiwipete(self):
+        b = Board()
+        self.load_fen("r3k2r/p1ppqpb1/bn2pnp1/3PN3/1p2P3/2N2Q1p/PPPBBPPP/R3K2R w KQkq - 0 1", board=b)
+        expected = {
+            1: 48,
+            2: 2039,
+            3: 97862
+        }
+        for d, want in expected.items():
+            got = int(perft(b, d))
+            self.assertEqual(got, want, f"perft({d}) kiwipete")
+    """