We remark that in current master, most of our use cases for between_bb() can be
optimized if the second parameter of the function is added to the segment. So we
change the definition of between_bb(s1, s2) such that it excludes s1 but includes s2.
We also use a precomputed array for between_bb() for another small speed gain
(see https://tests.stockfishchess.org/tests/view/
604d09f72433018de7a389fb).
Passed STC:
LLR: 2.96 (-2.94,2.94) {-0.25,1.25}
Total: 18736 W: 1746 L: 1607 D: 15383
Ptnml(0-2): 61, 1226, 6644, 1387, 50
https://tests.stockfishchess.org/tests/view/
60428c84ddcba5f0627bb6e4
Yellow LTC:
LTC:
LLR: -3.00 (-2.94,2.94) {0.25,1.25}
Total: 39144 W: 1431 L: 1413 D: 36300
Ptnml(0-2): 13, 1176, 17184, 1178, 21
https://tests.stockfishchess.org/tests/view/
605128702433018de7a38ca1
Closes https://github.com/official-stockfish/Stockfish/pull/3397
---------
Verified for correctness by running perft on the following position:
./stockfish
position fen 4rrk1/1p1nq3/p7/2p1P1pp/3P2bp/3Q1Bn1/PPPB4/1K2R1NR w - - 40 21
go perft 6
Nodes searched:
6136386434
--------
No functional change
Bitboard SquareBB[SQUARE_NB];
Bitboard LineBB[SQUARE_NB][SQUARE_NB];
+Bitboard BetweenBB[SQUARE_NB][SQUARE_NB];
Bitboard PseudoAttacks[PIECE_TYPE_NB][SQUARE_NB];
Bitboard PawnAttacks[COLOR_NB][SQUARE_NB];
for (PieceType pt : { BISHOP, ROOK })
for (Square s2 = SQ_A1; s2 <= SQ_H8; ++s2)
+ {
if (PseudoAttacks[pt][s1] & s2)
- LineBB[s1][s2] = (attacks_bb(pt, s1, 0) & attacks_bb(pt, s2, 0)) | s1 | s2;
+ {
+ LineBB[s1][s2] = (attacks_bb(pt, s1, 0) & attacks_bb(pt, s2, 0)) | s1 | s2;
+ BetweenBB[s1][s2] = (attacks_bb(pt, s1, square_bb(s2)) & attacks_bb(pt, s2, square_bb(s1)));
+ }
+ BetweenBB[s1][s2] |= s2;
+ }
}
}
extern uint8_t SquareDistance[SQUARE_NB][SQUARE_NB];
extern Bitboard SquareBB[SQUARE_NB];
+extern Bitboard BetweenBB[SQUARE_NB][SQUARE_NB];
extern Bitboard LineBB[SQUARE_NB][SQUARE_NB];
extern Bitboard PseudoAttacks[PIECE_TYPE_NB][SQUARE_NB];
extern Bitboard PawnAttacks[COLOR_NB][SQUARE_NB];
}
-/// between_bb() returns a bitboard representing squares that are linearly
-/// between the two given squares (excluding the given squares). If the given
-/// squares are not on a same file/rank/diagonal, we return 0. For instance,
-/// between_bb(SQ_C4, SQ_F7) will return a bitboard with squares D5 and E6.
+/// between_bb(s1, s2) 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) {
- Bitboard b = line_bb(s1, s2) & ((AllSquares << s1) ^ (AllSquares << s2));
- return b & (b - 1); //exclude lsb
+ assert(is_ok(s1) && is_ok(s2));
+ return BetweenBB[s1][s2];
}
-/// forward_ranks_bb() returns a bitboard representing the squares on the ranks
-/// in front of the given one, from the point of view of the given color. For instance,
+/// forward_ranks_bb() returns a bitboard representing the squares on 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.
constexpr Bitboard forward_ranks_bb(Color c, Square s) {
{
assert(rank_of(pos.ep_square()) == relative_rank(Us, RANK_6));
- // An en passant capture cannot resolve a discovered check.
+ // An en passant capture cannot resolve a discovered check
if (Type == EVASIONS && (target & (pos.ep_square() + Up)))
return moveList;
target = ~pos.pieces();
break;
case EVASIONS:
- target = between_bb(pos.square<KING>(Us), lsb(pos.checkers())) | pos.checkers();
+ target = between_bb(pos.square<KING>(Us), lsb(pos.checkers()));
break;
case NON_EVASIONS:
target = ~pos.pieces(Us);
if (more_than_one(pos.checkers()))
return moveList; // Double check, only a king move can save the day
- // Generate blocking evasions or captures of the checking piece
+ // Generate blocking interpositions or captures of the checking piece
return us == WHITE ? generate_all<WHITE, EVASIONS>(pos, moveList)
: generate_all<BLACK, EVASIONS>(pos, moveList);
}
Square kto = relative_square(c, cr & KING_SIDE ? SQ_G1 : SQ_C1);
Square rto = relative_square(c, cr & KING_SIDE ? SQ_F1 : SQ_D1);
- castlingPath[cr] = (between_bb(rfrom, rto) | between_bb(kfrom, kto) | rto | kto)
+ castlingPath[cr] = (between_bb(rfrom, rto) | between_bb(kfrom, kto))
& ~(kfrom | rfrom);
}
if (more_than_one(checkers()))
return false;
- // Our move must be a blocking evasion or a capture of the checking piece
- if (!((between_bb(lsb(checkers()), square<KING>(us)) | checkers()) & to))
+ // Our move must be a blocking interposition or a capture of the checking piece
+ if (!(between_bb(square<KING>(us), lsb(checkers())) & to))
return false;
}
// In case of king moves under check we have to remove king so as to catch
Square s1 = from_sq(move);
Square s2 = to_sq(move);
- if (!(between_bb(s1, s2) & pieces()))
+ if (!((between_bb(s1, s2) ^ s2) & pieces()))
{
if (ply > i)
return true;