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Greatly speedup has_mate_threat()

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Instead of loop across all legal moves to find a mate
loop across possible check moves only.

This reduces more then 10 times the number of moves to
check for a possible mate.

Also rename generate_checks() in generate_non_capture_checks()
so to better clarify what the function does.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba
2009-04-20 09:10:27 +02:00
parent 24485c96ec
commit 7c267587fc
4 changed files with 18 additions and 17 deletions
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25
src/position.cpp
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@@ -1903,20 +1903,13 @@ bool Position::is_mate() const {
/// Position::has_mate_threat() tests whether a given color has a mate in one
/// from the current position. This function is quite slow, but it doesn't
/// matter, because it is currently only called from PV nodes, which are rare.
/// from the current position.
bool Position::has_mate_threat(Color c) {
StateInfo st1, st2;
Color stm = side_to_move();
// The following lines are useless and silly, but prevents gcc from
// emitting a stupid warning stating that u1.lastMove and u1.epSquare might
// be used uninitialized.
st1.lastMove = st->lastMove;
st1.epSquare = st->epSquare;
if (is_check())
return false;
@@ -1927,18 +1920,26 @@ bool Position::has_mate_threat(Color c) {
MoveStack mlist[120];
int count;
bool result = false;
Bitboard dc = discovered_check_candidates(sideToMove);
Bitboard pinned = pinned_pieces(sideToMove);
// Generate legal moves
count = generate_legal_moves(*this, mlist);
// Generate pseudo-legal non-capture and capture check moves
count = generate_non_capture_checks(*this, mlist, dc);
count += generate_captures(*this, mlist + count);
// Loop through the moves, and see if one of them is mate
for (int i = 0; i < count; i++)
{
do_move(mlist[i].move, st2);
Move move = mlist[i].move;
if (!pl_move_is_legal(move, pinned))
continue;
do_move(move, st2);
if (is_mate())
result = true;
undo_move(mlist[i].move);
undo_move(move);
}
// Undo null move, if necessary