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Change definition of between_bb() 

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
pull/3404/head
bmc4 2021-03-15 16:06:42 -03:00 committed by Stéphane Nicolet
parent d58e83695f
commit 5089061659
4 changed files with 27 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
src/bitboard.cpp
View File

@ -29,6 +29,7 @@ uint8_t SquareDistance[SQUARE_NB][SQUARE_NB];
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];
@ -107,8 +108,14 @@ void Bitboards::init() {
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;
}
}
}

20
src/bitboard.h
View File

@ -75,6 +75,7 @@ extern uint8_t PopCnt16[1 << 16];
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];
@ -215,19 +216,22 @@ inline Bitboard line_bb(Square s1, Square s2) {
}
/// 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) {

6
src/movegen.cpp
View File

@ -158,7 +158,7 @@ namespace {
{
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;
@ -218,7 +218,7 @@ namespace {
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);
@ -329,7 +329,7 @@ ExtMove* generate<EVASIONS>(const Position& pos, ExtMove* moveList) {
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);
}

8
src/position.cpp
View File

@ -320,7 +320,7 @@ void Position::set_castling_right(Color c, Square rfrom) {
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);
}
@ -613,8 +613,8 @@ bool Position::pseudo_legal(const Move m) const {
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
@ -1218,7 +1218,7 @@ bool Position::has_game_cycle(int ply) const {
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;