-/// forward_ranks_bb() returns a bitboard representing the squares on all the ranks
-/// in front of the given one, from the point of view of the given color. For instance,
-/// forward_ranks_bb(BLACK, SQ_D3) will return the 16 squares on ranks 1 and 2.
-
-inline Bitboard forward_ranks_bb(Color c, Square s) {
- return ForwardRanksBB[c][rank_of(s)];
-}
-
+// Returns a bitboard representing the squares in the semi-open
+// segment between the squares s1 and s2 (excluding s1 but including s2). If the
+// given squares are not on a same file/rank/diagonal, it returns s2. For instance,
+// between_bb(SQ_C4, SQ_F7) will return a bitboard with squares D5, E6 and F7, but
+// between_bb(SQ_E6, SQ_F8) will return a bitboard with the square F8. This trick
+// allows to generate non-king evasion moves faster: the defending piece must either
+// interpose itself to cover the check or capture the checking piece.
+inline Bitboard between_bb(Square s1, Square s2) {