diff --git a/src/chessdefs.h-move-to-temp-migration-bitboard__chessdefs.h b/src/chessdefs.h-move-to-temp-migration-bitboard__chessdefs.h
new file mode 100644
index 0000000..889520e
--- /dev/null
+++ b/src/chessdefs.h-move-to-temp-migration-bitboard__chessdefs.h
@@ -0,0 +1,129 @@
+/* chessdefs.h - generic chess definitions.
+ *
+ * Copyright (C) 2021 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 CHESSDEFS_H
+#define CHESSDEFS_H
+
+#include "br.h"
+
+/* piece_t bits structure
+ * MSB 8 7 6 5 4 3 2 1 LSB
+ * 1: color (0 for white)
+ * 2-7: bit set for pawn (2), knight, bishop, rook, queen, king (7)
+ */
+typedef u8 piece_t;
+
+enum {
+    E_EMPTY = 0,
+    E_COLOR,                                      /* LSB */
+    E_PAWN,
+    E_KNIGHT,
+    E_BISHOP,
+    E_ROOK,
+    E_QUEEN,
+    E_KING,
+};
+
+/* pos_t bitboards tables
+ */
+enum {
+    BB_ALL = 0,                                   /* OR of all bitboards */
+    BB_UNUSED,                                    /* future use ? */
+    BB_PAWN = E_PAWN,
+    BB_KNIGHT,
+    BB_BISHOP,
+    BB_ROOK,
+    BB_QUEEN,
+    BB_KING,
+    BB_END
+};
+
+/* piece bitmask in piece_t
+ */
+enum {
+    EMPTY  = 0,
+    PAWN   = 1 << (E_PAWN - 1),                   /* 1<<(2-1) = 0x02 00000010 */
+    KNIGHT = 1 << (E_KNIGHT - 1),                 /* 0x04 00000100 */
+    BISHOP = 1 << (E_BISHOP - 1),                 /* 0x08 00001000 */
+    ROOK   = 1 << (E_ROOK - 1),                   /* 0x10 00010000 */
+    QUEEN  = 1 << (E_QUEEN - 1),                  /* 0x20 00100000 */
+    KING   = 1 << (E_KING - 1),                   /* 0x40 01000000 */
+};
+
+#define PIECETOBB(p)    (ffs64(PIECE(p)))         /* from piece_t to bb piece array */
+
+#define WHITE           0                         /* 0x00 00000000 */
+#define BLACK           1                         /* 0x01 00000001 */
+#define OPPONENT(p)     !(p)
+
+#define MASK_COLOR      0x01                      /* 00000001 */
+#define MASK_PIECE      0x7E                      /* 01111110 */
+
+#define COLOR(p)        ((p) & MASK_COLOR)        /* bitmask */
+#define PIECE(p)        ((p) & MASK_PIECE)
+#define E_PIECE(p)      (ffs64(PIECE(p)))         /* convert mask to E_XX */
+
+#define IS_WHITE(p)     (!COLOR(p))
+#define IS_BLACK(p)     (COLOR(p))
+
+#define SET_WHITE(p)    ((p) &= ~MASK_COLOR)
+#define SET_BLACK(p)    ((p) |= MASK_COLOR)
+#define SET_COLOR(p, c) (!(c)? SET_WHITE(p): SET_BLACK(p))
+
+/* flip a 0-63 square:
+ * Vertical:   G8 (62) becomes G1 (6)
+ * Horizontal: G8 (62) becomes B8 (57)
+ */
+#define FLIP_V(sq)      ((sq) ^ 56)
+#define FLIP_H(sq)      ((sq) ^ 7)
+/* square_t bits structure : rrrrffff
+ * ffff: file
+ * rrrr: rank
+ */
+typedef uchar square_t;
+
+/* castle_t bits structure
+ */
+typedef unsigned char castle_t;
+
+#define CASTLE_WK       (1 << 0)                  /* 0x01 00000001 */
+#define CASTLE_WQ       (1 << 1)                  /* 0x02 00000010 */
+#define CASTLE_BK       (1 << 2)                  /* 0x04 00000100 */
+#define CASTLE_BQ       (1 << 3)                  /* 0x08 00001000 */
+
+#define CASTLE_W        (CASTLE_WK | CASTLE_WQ)   /* 00000011 W castle mask */
+#define CASTLE_B        (CASTLE_BK | CASTLE_BQ)   /* 00001100 B castle mask */
+
+/* game phases
+ */
+#define OPENING    0
+#define MIDDLEGAME 1
+#define ENDGAME    2
+
+/* bitboard
+ */
+typedef u64 bitboard_t;
+
+
+/* eval type
+ */
+typedef s32 eval_t;
+
+/* forward typedefs
+ */
+typedef struct piece_list_s piece_list_t;
+typedef struct board_s board_t;
+typedef struct pos_s pos_t;
+typedef struct move_s move_t;
+
+#endif