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Do not prune useless checks in QS

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Passed both SPRT tests in "simplification mode", so with
elo0: -3.00 alpha: 0.05 elo1: 3.00 beta: 0.05

Short TC:
LLR: 2.96 (-2.94,2.94)
Total: 6243 W: 1302 L: 1195 D: 3746

Long TC
LLR: 2.96 (-2.94,2.94)
Total: 22972 W: 4124 L: 4020 D: 14828

bench: 4633330
This commit is contained in:
Lucas Braesch 2013-09-05 07:26:05 +08:00 • committed by Marco Costalba
parent a30d3571ca
commit 10b53e1c5e
1 changed files with 0 additions and 47 deletions
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47
src/search.cpp
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@ -99,7 +99,6 @@ namespace {
void id_loop(Position& pos);
Value value_to_tt(Value v, int ply);
Value value_from_tt(Value v, int ply);
bool check_is_dangerous(const Position& pos, Move move, Value futilityBase, Value beta);
bool allows(const Position& pos, Move first, Move second);
bool refutes(const Position& pos, Move first, Move second);
string uci_pv(const Position& pos, int depth, Value alpha, Value beta);
@ -1267,16 +1266,6 @@ moves_loop: // When in check and at SpNode search starts from here
&& pos.see_sign(move) < 0)
continue;
// Don't search useless checks
if ( !PvNode
&& !InCheck
&& givesCheck
&& move != ttMove
&& !pos.is_capture_or_promotion(move)
&& ss->staticEval + PawnValueMg / 4 < beta
&& !check_is_dangerous(pos, move, futilityBase, beta))
continue;
// Check for legality only before to do the move
if (!pos.pl_move_is_legal(move, ci.pinned))
continue;
@ -1354,42 +1343,6 @@ moves_loop: // When in check and at SpNode search starts from here
}
// check_is_dangerous() tests if a checking move can be pruned in qsearch()
bool check_is_dangerous(const Position& pos, Move move, Value futilityBase, Value beta)
{
Piece pc = pos.piece_moved(move);
Square from = from_sq(move);
Square to = to_sq(move);
Color them = ~pos.side_to_move();
Square ksq = pos.king_square(them);
Bitboard enemies = pos.pieces(them);
Bitboard kingAtt = pos.attacks_from<KING>(ksq);
Bitboard occ = pos.pieces() ^ from ^ ksq;
Bitboard oldAtt = pos.attacks_from(pc, from, occ);
Bitboard newAtt = pos.attacks_from(pc, to, occ);
// Checks which give opponent's king at most one escape square are dangerous
if (!more_than_one(kingAtt & ~(enemies | newAtt | to)))
return true;
// Queen contact check is very dangerous
if (type_of(pc) == QUEEN && (kingAtt & to))
return true;
// Creating new double threats with checks is dangerous
Bitboard b = (enemies ^ ksq) & newAtt & ~oldAtt;
while (b)
{
// Note that here we generate illegal "double move"!
if (futilityBase + PieceValue[EG][pos.piece_on(pop_lsb(&b))] >= beta)
return true;
}
return false;
}
// allows() tests whether the 'first' move at previous ply somehow makes the
// 'second' move possible, for instance if the moving piece is the same in
// both moves. Normally the second move is the threat (the best move returned