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Code Issues Releases Wiki Activity

Simplify away SEE verification

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After 4 simplificatons over PR#4453 the idea does not yield significant
improvement anymore. Maybe also
https://tests.stockfishchess.org/tests/view/640c88092644b62c3394c1c5 was
a fluke.

Passed non-regression bounds:

STC:
https://tests.stockfishchess.org/tests/view/64705389c079b6583146d873
LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 131936 W: 35040 L: 34930 D: 61966
Ptnml(0-2): 336, 14559, 36035, 14735, 303

LTC:
https://tests.stockfishchess.org/tests/view/6471a2ade549d9cf2fb213cd
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 407700 W: 109999 L: 110164 D: 187537
Ptnml(0-2): 279, 39913, 123689, 39632, 337

closes https://github.com/official-stockfish/Stockfish/pull/4595

bench: 2675974
This commit is contained in:
Guenther Demetz 2023-05-31 11:48:18 +02:00 • committed by Joost VandeVondele
parent 6cf8d938c5
commit 5930c0defb
3 changed files with 8 additions and 30 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

19
src/position.cpp
View file

@ -1061,7 +1061,7 @@ Key Position::key_after(Move m) const {
/// SEE value of move is greater or equal to the given threshold. We'll use an
/// algorithm similar to alpha-beta pruning with a null window.
bool Position::see_ge(Move m, Bitboard& occupied, Value threshold) const {
bool Position::see_ge(Move m, Value threshold) const {
assert(is_ok(m));
@ -1080,7 +1080,7 @@ bool Position::see_ge(Move m, Bitboard& occupied, Value threshold) const {
return true;
assert(color_of(piece_on(from)) == sideToMove);
occupied = pieces() ^ from ^ to; // xoring to is important for pinned piece logic
Bitboard occupied = pieces() ^ from ^ to; // xoring to is important for pinned piece logic
Color stm = sideToMove;
Bitboard attackers = attackers_to(to, occupied);
Bitboard stmAttackers, bb;
@ -1111,43 +1111,43 @@ bool Position::see_ge(Move m, Bitboard& occupied, Value threshold) const {
// the bitboard 'attackers' any X-ray attackers behind it.
if ((bb = stmAttackers & pieces(PAWN)))
{
occupied ^= least_significant_square_bb(bb);
if ((swap = PawnValueMg - swap) < res)
break;
occupied ^= least_significant_square_bb(bb);
attackers |= attacks_bb<BISHOP>(to, occupied) & pieces(BISHOP, QUEEN);
}
else if ((bb = stmAttackers & pieces(KNIGHT)))
{
occupied ^= least_significant_square_bb(bb);
if ((swap = KnightValueMg - swap) < res)
break;
occupied ^= least_significant_square_bb(bb);
}
else if ((bb = stmAttackers & pieces(BISHOP)))
{
occupied ^= least_significant_square_bb(bb);
if ((swap = BishopValueMg - swap) < res)
break;
occupied ^= least_significant_square_bb(bb);
attackers |= attacks_bb<BISHOP>(to, occupied) & pieces(BISHOP, QUEEN);
}
else if ((bb = stmAttackers & pieces(ROOK)))
{
occupied ^= least_significant_square_bb(bb);
if ((swap = RookValueMg - swap) < res)
break;
occupied ^= least_significant_square_bb(bb);
attackers |= attacks_bb<ROOK>(to, occupied) & pieces(ROOK, QUEEN);
}
else if ((bb = stmAttackers & pieces(QUEEN)))
{
occupied ^= least_significant_square_bb(bb);
if ((swap = QueenValueMg - swap) < res)
break;
occupied ^= least_significant_square_bb(bb);
attackers |= (attacks_bb<BISHOP>(to, occupied) & pieces(BISHOP, QUEEN))
| (attacks_bb<ROOK >(to, occupied) & pieces(ROOK , QUEEN));
@ -1162,11 +1162,6 @@ bool Position::see_ge(Move m, Bitboard& occupied, Value threshold) const {
return bool(res);
}
bool Position::see_ge(Move m, Value threshold) const {
Bitboard occupied;
return see_ge(m, occupied, threshold);
}
/// Position::is_draw() tests whether the position is drawn by 50-move rule
/// or by repetition. It does not detect stalemates.

1
src/position.h
View file

@ -143,7 +143,6 @@ public:
void undo_null_move();
// Static Exchange Evaluation
bool see_ge(Move m, Bitboard& occupied, Value threshold = VALUE_ZERO) const;
bool see_ge(Move m, Value threshold = VALUE_ZERO) const;
// Accessing hash keys

18
src/search.cpp
View file

@ -989,25 +989,9 @@ moves_loop: // When in check, search starts here
+ captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))] / 7 < alpha)
continue;
Bitboard occupied;
// SEE based pruning (~11 Elo)
if (!pos.see_ge(move, occupied, Value(-212) * depth))
{
// Don't prune the move if opponent King/Queen/Rook gets a discovered attack during or after the exchanges
Bitboard leftEnemies = pos.pieces(~us, KING, QUEEN, ROOK);
Bitboard attacks = 0;
occupied |= to_sq(move);
while (leftEnemies && !attacks)
{
Square sq = pop_lsb(leftEnemies);
attacks = pos.attackers_to(sq, occupied) & pos.pieces(us) & occupied;
// Exclude Queen/Rook(s) which were already threatened before SEE (opponent King can't be in check when it's our turn)
if (attacks && sq != pos.square<KING>(~us) && (pos.attackers_to(sq, pos.pieces()) & pos.pieces(us)))
attacks = 0;
}
if (!attacks)
if (!pos.see_ge(move, Value(-205) * depth))
continue;
}
}
else
{