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Change definition of between_bb()

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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
This commit is contained in:
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
Download Patch File Download Diff File Expand all files Collapse all files

20
src/bitboard.h
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@@ -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) {