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Optimize generate_evasions()

Browse source 
Generate captures of checking piece and blocking
evasions in one go.

Also reduce of one indentation level early returning
when we have a double check.

Verified with perft no functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2009-11-02 16:33:54 +01:00
parent 483a257618
commit 53c2bf0697
1 changed files with 54 additions and 70 deletions
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42
src/movegen.cpp
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@ -246,14 +246,14 @@ MoveStack* generate_evasions(const Position& pos, MoveStack* mlist, Bitboard pin
// Generate evasions for other pieces only if not double check. We use a
// simple bit twiddling hack here rather than calling count_1s in order to
// save some time (we know that pos.checkers() has at most two nonzero bits).
if (!(checkers & (checkers - 1))) // Only one bit set?
{
if (checkers & (checkers - 1)) // Two bits set?
return mlist;
Square checksq = first_1(checkers);
Bitboard target = squares_between(checksq, ksq);
assert(pos.color_of_piece_on(checksq) == them);
// Generate captures of the checking piece
// Pawn captures
b1 = pos.attacks_from<PAWN>(checksq, them) & pos.pieces(PAWN, us) & ~pinned;
while (b1)
@ -269,33 +269,18 @@ MoveStack* generate_evasions(const Position& pos, MoveStack* mlist, Bitboard pin
(*mlist++).move = make_move(from, checksq);
}
// Pieces captures
b1 = ( (pos.attacks_from<KNIGHT>(checksq) & pos.pieces(KNIGHT, us))
| (pos.attacks_from<BISHOP>(checksq) & pos.pieces(BISHOP, QUEEN, us))
| (pos.attacks_from<ROOK>(checksq) & pos.pieces(ROOK, QUEEN, us)) ) & ~pinned;
while (b1)
{
from = pop_1st_bit(&b1);
(*mlist++).move = make_move(from, checksq);
}
// Blocking check evasions are possible only if the checking piece is a slider
// Pawn blocking evasions (possible only if the checking piece is a slider)
if (sliderAttacks)
{
Bitboard blockSquares = squares_between(checksq, ksq);
mlist = generate_piece_evasions<PAWN>(pos, mlist, us, target, pinned);
assert((pos.occupied_squares() & blockSquares) == EmptyBoardBB);
// Add the checking piece to the target squares
target |= checkers;
if (blockSquares)
{
mlist = generate_piece_evasions<PAWN>(pos, mlist, us, blockSquares, pinned);
mlist = generate_piece_evasions<KNIGHT>(pos, mlist, us, blockSquares, pinned);
mlist = generate_piece_evasions<BISHOP>(pos, mlist, us, blockSquares, pinned);
mlist = generate_piece_evasions<ROOK>(pos, mlist, us, blockSquares, pinned);
mlist = generate_piece_evasions<QUEEN>(pos, mlist, us, blockSquares, pinned);
}
}
// Captures and blocking evasions for the other pieces
mlist = generate_piece_evasions<KNIGHT>(pos, mlist, us, target, pinned);
mlist = generate_piece_evasions<BISHOP>(pos, mlist, us, target, pinned);
mlist = generate_piece_evasions<ROOK>(pos, mlist, us, target, pinned);
mlist = generate_piece_evasions<QUEEN>(pos, mlist, us, target, pinned);
// Finally, the special case of en passant captures. An en passant
// capture can only be a check evasion if the check is not a discovered
@ -322,7 +307,6 @@ MoveStack* generate_evasions(const Position& pos, MoveStack* mlist, Bitboard pin
(*mlist++).move = make_ep_move(from, to);
}
}
}
return mlist;
}