ss->ttPv = PvNode || (ss->ttHit && tte->is_pv());
formerPv = ss->ttPv && !PvNode;
+ // Update low ply history for previous move if we are near root and position is or has been in PV
if ( ss->ttPv
&& depth > 12
&& ss->ply - 1 < MAX_LPH
{
if (ttValue >= beta)
{
+ // Bonus for a quiet ttMove that fails high
if (!pos.capture_or_promotion(ttMove))
update_quiet_stats(pos, ss, ttMove, stat_bonus(depth), depth);
}
}
+ // Partial workaround for the graph history interaction problem
+ // For high rule50 counts don't produce transposition table cutoffs.
if (pos.rule50_count() < 90)
return ttValue;
}
if (eval == VALUE_NONE)
ss->staticEval = eval = evaluate(pos);
+ // Randomize draw evaluation
if (eval == VALUE_DRAW)
eval = value_draw(thisThread);
}
else
{
+ // In case of null move search use previous static eval with a different sign
+ // and addition of two tempos
if ((ss-1)->currentMove != MOVE_NULL)
ss->staticEval = eval = evaluate(pos);
else
ss->staticEval = eval = -(ss-1)->staticEval + 2 * Tempo;
+ // Save static evaluation into transposition table
tte->save(posKey, VALUE_NONE, ss->ttPv, BOUND_NONE, DEPTH_NONE, MOVE_NONE, eval);
}
- // Update static history for previous move
+ // Use static evaluation difference to improve quiet move ordering
if (is_ok((ss-1)->currentMove) && !(ss-1)->inCheck && !priorCapture)
{
- int bonus = ss->staticEval > -(ss-1)->staticEval + 2 * Tempo ? -stat_bonus(depth) :
- ss->staticEval < -(ss-1)->staticEval + 2 * Tempo ? stat_bonus(depth) :
- 0;
- thisThread->staticHistory[~us][from_to((ss-1)->currentMove)] << bonus;
+ int bonus = std::clamp(-depth * 4 * int((ss-1)->staticEval + ss->staticEval - 2 * Tempo), -1000, 1000);
+ thisThread->mainHistory[~us][from_to((ss-1)->currentMove)] << bonus;
}
// Step 7. Razoring (~1 Elo)
&& eval <= alpha - RazorMargin)
return qsearch<NT>(pos, ss, alpha, beta);
+ // Set up improving flag that is used in various pruning heuristics
+ // We define position as improving if static evaluation of position is better
+ // Than the previous static evaluation at our turn
+ // In case of us being in check at our previous move we look at move prior to it
improving = (ss-2)->staticEval == VALUE_NONE
? ss->staticEval > (ss-4)->staticEval || (ss-4)->staticEval == VALUE_NONE
: ss->staticEval > (ss-2)->staticEval;
Move countermove = thisThread->counterMoves[pos.piece_on(prevSq)][prevSq];
MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
- &thisThread->staticHistory,
&thisThread->lowPlyHistory,
&captureHistory,
contHist,
|| moveCountPruning
|| ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha
|| cutNode
+ || (!PvNode && !formerPv && thisThread->captureHistory[movedPiece][to_sq(move)][type_of(pos.captured_piece())] < 4506)
|| thisThread->ttHitAverage < 432 * TtHitAverageResolution * TtHitAverageWindow / 1024))
{
Depth r = reduction(improving, depth, moveCount);
r -= 2;
// Increase reduction at root and non-PV nodes when the best move does not change frequently
- if ((rootNode || !PvNode) && depth > 10 && thisThread->bestMoveChanges <= 2)
+ if ((rootNode || !PvNode) && thisThread->rootDepth > 10 && thisThread->bestMoveChanges <= 2)
r++;
+ // More reductions for late moves if position was not in previous PV
if (moveCountPruning && !formerPv)
r++;
{
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
+ // If the move passed LMR update its stats
if (didLMR && !captureOrPromotion)
{
int bonus = value > alpha ? stat_bonus(newDepth)
rm.pv.push_back(*m);
// We record how often the best move has been changed in each
- // iteration. This information is used for time management: when
- // the best move changes frequently, we allocate some more time.
+ // iteration. This information is used for time management and LMR
if (moveCount > 1)
++thisThread->bestMoveChanges;
}
}
}
+ // If the move is worse than some previously searched move, remember it to update its stats later
if (move != bestMove)
{
if (captureOrPromotion && captureCount < 32)
bestValue = excludedMove ? alpha
: ss->inCheck ? mated_in(ss->ply) : VALUE_DRAW;
+ // If there is a move which produces search value greater than alpha we update stats of searched moves
else if (bestMove)
update_all_stats(pos, ss, bestMove, bestValue, beta, prevSq,
quietsSearched, quietCount, capturesSearched, captureCount, depth);
else if (depth > 3)
ss->ttPv = ss->ttPv && (ss+1)->ttPv;
+ // Write gathered information in transposition table
if (!excludedMove && !(rootNode && thisThread->pvIdx))
tte->save(posKey, value_to_tt(bestValue, ss->ply), ss->ttPv,
bestValue >= beta ? BOUND_LOWER :
bestValue = ttValue;
}
else
+ // In case of null move search use previous static eval with a different sign
+ // and addition of two tempos
ss->staticEval = bestValue =
(ss-1)->currentMove != MOVE_NULL ? evaluate(pos)
: -(ss-1)->staticEval + 2 * Tempo;
// Stand pat. Return immediately if static value is at least beta
if (bestValue >= beta)
{
+ // Save gathered info in transposition table
if (!ss->ttHit)
tte->save(posKey, value_to_tt(bestValue, ss->ply), false, BOUND_LOWER,
DEPTH_NONE, MOVE_NONE, ss->staticEval);
// queen and checking knight promotions, and other checks(only if depth >= DEPTH_QS_CHECKS)
// will be generated.
MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
- &thisThread->staticHistory,
&thisThread->captureHistory,
contHist,
to_sq((ss-1)->currentMove));
return mated_in(ss->ply); // Plies to mate from the root
}
+ // Save gathered info in transposition table
tte->save(posKey, value_to_tt(bestValue, ss->ply), pvHit,
bestValue >= beta ? BOUND_LOWER :
PvNode && bestValue > oldAlpha ? BOUND_EXACT : BOUND_UPPER,
if (!pos.capture_or_promotion(bestMove))
{
+ // Increase stats for the best move in case it was a quiet move
update_quiet_stats(pos, ss, bestMove, bonus2, depth);
- // Decrease all the non-best quiet moves
+ // Decrease stats for all non-best quiet moves
for (int i = 0; i < quietCount; ++i)
{
thisThread->mainHistory[us][from_to(quietsSearched[i])] << -bonus2;
}
}
else
+ // Increase stats for the best move in case it was a capture move
captureHistory[moved_piece][to_sq(bestMove)][captured] << bonus1;
- // Extra penalty for a quiet early move that was not a TT move or main killer move in previous ply when it gets refuted
+ // Extra penalty for a quiet early move that was not a TT move or
+ // main killer move in previous ply when it gets refuted.
if ( ((ss-1)->moveCount == 1 + (ss-1)->ttHit || ((ss-1)->currentMove == (ss-1)->killers[0]))
&& !pos.captured_piece())
update_continuation_histories(ss-1, pos.piece_on(prevSq), prevSq, -bonus1);
- // Decrease all the non-best capture moves
+ // Decrease stats for all non-best capture moves
for (int i = 0; i < captureCount; ++i)
{
moved_piece = pos.moved_piece(capturesSearched[i]);
for (int i : {1, 2, 4, 6})
{
+ // Only update first 2 continuation histories if we are in check
if (ss->inCheck && i > 2)
break;
if (is_ok((ss-i)->currentMove))
void update_quiet_stats(const Position& pos, Stack* ss, Move move, int bonus, int depth) {
+ // Update killers
if (ss->killers[0] != move)
{
ss->killers[1] = ss->killers[0];
thisThread->mainHistory[us][from_to(move)] << bonus;
update_continuation_histories(ss, pos.moved_piece(move), to_sq(move), bonus);
+ // Penalty for reversed move in case of moved piece not being a pawn
if (type_of(pos.moved_piece(move)) != PAWN)
thisThread->mainHistory[us][from_to(reverse_move(move))] << -bonus;
+ // Update countermove history
if (is_ok((ss-1)->currentMove))
{
Square prevSq = to_sq((ss-1)->currentMove);
thisThread->counterMoves[pos.piece_on(prevSq)][prevSq] = move;
}
+ // Update low ply history
if (depth > 11 && ss->ply < MAX_LPH)
thisThread->lowPlyHistory[ss->ply][from_to(move)] << stat_bonus(depth - 7);
}
projects / stockfish / blobdiff