start bitboard init (see commit details)

- bitboard.c: make attacks for knight/king
- square macros (BB, BBfile, BBrank) renamed sq_make, sq_file,
  sq_rank, moved to board.h (and become temporarily inline funcs)
- different macros/defs moved to "correct place" (bitboard/board/piece):
  board.[ch]: everything related to board/square
  bitboard.[ch]: everything related to bitboards
  piece.[ch]: everything related to pieces

src/board.h

@@ -1,6 +1,6 @@
-/* board.h - board definitions.
+/* board.h - 8x8 board definitions.
  *
- * Copyright (C) 2021 Bruno Raoult ("br")
+ * Copyright (C) 2021-2024 Bruno Raoult ("br")
  * Licensed under the GNU General Public License v3.0 or later.
  * Some rights reserved. See COPYING.
  *
@@ -17,6 +17,83 @@
 #include "brlib.h"
 
 #include "chessdefs.h"
+
+typedef enum {
+    _SSQUARE_ = -1,                               /* force signed enum */
+    A1 = 0, B1, C1, D1, E1, F1, G1, H1,
+    A2, B2, C2, D2, E2, F2, G2, H2,
+    A3, B3, C3, D3, E3, F3, G3, H3,
+    A4, B4, C4, D4, E4, F4, G4, H4,
+    A5, B5, C5, D5, E5, F5, G5, H5,
+    A6, B6, C6, D6, E6, F6, G6, H6,
+    A7, B7, C7, D7, E7, F7, G7, H7,
+    A8, B8, C8, D8, E8, F8, G8, H8,
+    SQUARE_MAX = 64,
+    SQUARE_NONE = 64
+} square_t;
+
+typedef enum {
+    _SFILE_ = -1,                                 /* force signed enum */
+    FILE_A = 0, FILE_B, FILE_C, FILE_D, FILE_E, FILE_F, FILE_G, FILE_H,
+    FILE_MAX,
+} file_t;
+
+typedef enum {
+    _SRANK_ = -1,                                 /* force signed enum */
+    RANK_1 = 0, RANK_2, RANK_3, RANK_4, RANK_5, RANK_6, RANK_7, RANK_8,
+    RANK_MAX,
+} rank_t;
+
+typedef enum {
+    NORTH = 8,
+    EAST =  1,
+    SOUTH = -NORTH,
+    WEST = -EAST,
+
+    NORTH_EAST = (NORTH + EAST),
+    SOUTH_EAST = (SOUTH + EAST),
+    SOUTH_WEST = (SOUTH + WEST),
+    NORTH_WEST = (NORTH + WEST),
+} dir_t;
+
+/* 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)
+#define FLIP_HV(sq)     (FLIP_V(FLIP_H(sq)))
+
+/* TODO: revert to macros after bitboard migration */
+static __always_inline square_t sq_make(file_t file, rank_t rank)
+{
+    return (rank << 3) + file;
+}
+static __always_inline file_t sq_file(square_t square)
+{
+    return square & 7;
+}
+static __always_inline rank_t sq_rank(square_t square)
+{
+    return square >> 3;
+}
+
+
+#define sq_ok(sq)       ((sq) >= A1 && (sq) <= H8)
+
+/* Chebyshev distance: https://www.chessprogramming.org/Distance */
+#define sq_dist(sq1, sq2) (max(abs(sq_file(sq2) - sq_file(sq1)),  \
+                               abs(sq_rank(sq2) - sq_rank(sq1))))
+/* Manhattan distance */
+#define sq_manh(sq1, sq2) (abs(sq_file(sq2) - sq_file(sq1)) +     \
+                           abs(sq_rank(sq2) - sq_rank(sq1)))
+
+// while the orthogonal Manhattan-Distance is the sum of both absolute rank- and file-distance distances.
+
+//Dtaxi = |r2 - r1| + |f2 - f1|
+
+// Chebyshev Distance
+
 //#include "piece.h"
 
 /* definitions for 0x88 representation