#include "uci.h"
#include "syzygy/tbprobe.h"
+namespace Stockfish {
+
namespace Search {
LimitsType Limits;
// History and stats update bonus, based on depth
int stat_bonus(Depth d) {
- return d > 14 ? 29 : 8 * d * d + 224 * d - 215;
+ return d > 14 ? 66 : 6 * d * d + 231 * d - 206;
}
// Add a small random component to draw evaluations to avoid 3-fold blindness
while (true)
{
Depth adjustedDepth = std::max(1, rootDepth - failedHighCnt - searchAgainCounter);
- bestValue = ::search<PV>(rootPos, ss, alpha, beta, adjustedDepth, false);
+ bestValue =
Stockfish::search<PV>(rootPos, ss, alpha, beta, adjustedDepth, false);
// Bring the best move to the front. It is critical that sorting
// is done with a stable algorithm because all the values but the
// Step 1. Initialize node
Thread* thisThread = pos.this_thread();
- ss->inCheck = pos.checkers();
- priorCapture = pos.captured_piece();
- Color us = pos.side_to_move();
- moveCount = captureCount = quietCount = ss->moveCount = 0;
- bestValue = -VALUE_INFINITE;
- maxValue = VALUE_INFINITE;
+ ss->inCheck = pos.checkers();
+ priorCapture = pos.captured_piece();
+ Color us = pos.side_to_move();
+ moveCount = captureCount = quietCount = ss->moveCount = 0;
+ bestValue = -VALUE_INFINITE;
+ maxValue = VALUE_INFINITE;
+ ss->distanceFromPv = (PvNode ? 0 : ss->distanceFromPv);
// Check for the available remaining time
if (thisThread == Threads.main())
// Step 8. Null move search with verification search (~40 Elo)
if ( !PvNode
&& (ss-1)->currentMove != MOVE_NULL
- && (ss-1)->statScore < 22977
+ && (ss-1)->statScore < 24185
&& eval >= beta
&& eval >= ss->staticEval
- && ss->staticEval >= beta - 30 * depth - 28 * improving + 84 * ss->ttPv + 168
+ && ss->staticEval >= beta - 24 * depth - 34 * improving + 162 * ss->ttPv + 159
&& !excludedMove
&& pos.non_pawn_material(us)
&& (ss->ply >= thisThread->nmpMinPly || us != thisThread->nmpColor))
assert(eval - beta >= 0);
// Null move dynamic reduction based on depth and value
- Depth R = (1015 + 85 * depth) / 256 + std::min(int(eval - beta) / 191, 3);
+ Depth R = (1062 + 68 * depth) / 256 + std::min(int(eval - beta) / 190, 3);
ss->currentMove = MOVE_NULL;
ss->continuationHistory = &thisThread->continuationHistory[0][0][NO_PIECE][0];
}
}
- probCutBeta = beta + 194 - 49 * improving;
+ probCutBeta = beta + 209 - 44 * improving;
// Step 9. ProbCut (~10 Elo)
// If we have a good enough capture and a reduced search returns a value
return probCutBeta;
assert(probCutBeta < VALUE_INFINITE);
+
MovePicker mp(pos, ttMove, probCutBeta - ss->staticEval, &captureHistory);
int probCutCount = 0;
bool ttPv = ss->ttPv;
moves_loop: // When in check, search starts from here
+ ttCapture = ttMove && pos.capture_or_promotion(ttMove);
+
+ // Step 11. A small Probcut idea, when we are in check
+ probCutBeta = beta + 400;
+ if ( ss->inCheck
+ && !PvNode
+ && depth >= 4
+ && ttCapture
+ && (tte->bound() & BOUND_LOWER)
+ && tte->depth() >= depth - 3
+ && ttValue >= probCutBeta
+ && abs(ttValue) <= VALUE_KNOWN_WIN
+ && abs(beta) <= VALUE_KNOWN_WIN
+ )
+ return probCutBeta;
+
+
const PieceToHistory* contHist[] = { (ss-1)->continuationHistory, (ss-2)->continuationHistory,
nullptr , (ss-4)->continuationHistory,
nullptr , (ss-6)->continuationHistory };
value = bestValue;
singularQuietLMR = moveCountPruning = false;
- ttCapture = ttMove && pos.capture_or_promotion(ttMove);
// Mark this node as being searched
ThreadHolding th(thisThread, posKey, ss->ply);
- // Step 11. Loop through all pseudo-legal moves until no moves remain
+ // Step 12. Loop through all pseudo-legal moves until no moves remain
// or a beta cutoff occurs.
while ((move = mp.next_move(moveCountPruning)) != MOVE_NONE)
{
movedPiece = pos.moved_piece(move);
givesCheck = pos.gives_check(move);
+ // Indicate PvNodes that will probably fail low if node was searched with non-PV search
+ // at depth equal or greater to current depth and result of this search was far below alpha
+ bool likelyFailLow = PvNode
+ && ttMove
+ && (tte->bound() & BOUND_UPPER)
+ && ttValue < alpha + 200 + 100 * depth
+ && tte->depth() >= depth;
+
// Calculate new depth for this move
newDepth = depth - 1;
- // Step 12. Pruning at shallow depth (~200 Elo)
+ // Step 13. Pruning at shallow depth (~200 Elo)
if ( !rootNode
&& pos.non_pawn_material(us)
&& bestValue > VALUE_TB_LOSS_IN_MAX_PLY)
// Futility pruning: parent node (~5 Elo)
if ( lmrDepth < 7
&& !ss->inCheck
- && ss->staticEval + 254 + 159 * lmrDepth <= alpha
+ && ss->staticEval + 174 + 157 * lmrDepth <= alpha
&& (*contHist[0])[movedPiece][to_sq(move)]
+ (*contHist[1])[movedPiece][to_sq(move)]
+ (*contHist[3])[movedPiece][to_sq(move)]
- + (*contHist[5])[movedPiece][to_sq(move)] / 2 < 26394)
+ + (*contHist[5])[movedPiece][to_sq(move)] / 3 < 28255)
continue;
// Prune moves with negative SEE (~20 Elo)
}
}
- // Step 13. Extensions (~75 Elo)
+ // Step 14. Extensions (~75 Elo)
// Singular extension search (~70 Elo). If all moves but one fail low on a
// search of (alpha-s, beta-s), and just one fails high on (alpha, beta),
{
Value singularBeta = ttValue - ((formerPv + 4) * depth) / 2;
Depth singularDepth = (depth - 1 + 3 * formerPv) / 2;
+
ss->excludedMove = move;
value = search<NonPV>(pos, ss, singularBeta - 1, singularBeta, singularDepth, cutNode);
ss->excludedMove = MOVE_NONE;
[movedPiece]
[to_sq(move)];
- // Step 14. Make the move
+ // Step 15. Make the move
pos.do_move(move, st, givesCheck);
- // Step 15. Reduced depth search (LMR, ~200 Elo). If the move fails high it will be
- // re-searched at full depth.
+ (ss+1)->distanceFromPv = ss->distanceFromPv + moveCount - 1;
+
+ // Step 16. Late moves reduction / extension (LMR, ~200 Elo)
+ // We use various heuristics for the sons of a node after the first son has
+ // been searched. In general we would like to reduce them, but there are many
+ // cases where we extend a son if it has good chances to be "interesting".
if ( depth >= 3
&& moveCount > 1 + 2 * rootNode
&& ( !captureOrPromotion
|| moveCountPruning
|| ss->staticEval + PieceValue[EG][pos.captured_piece()] <= alpha
|| cutNode
- || (!PvNode && !formerPv && captureHistory[movedPiece][to_sq(move)][type_of(pos.captured_piece())] < 4506)
+ || (!PvNode && !formerPv && captureHistory[movedPiece][to_sq(move)][type_of(pos.captured_piece())] < 3678)
|| thisThread->ttHitAverage < 432 * TtHitAverageResolution * TtHitAverageWindow / 1024))
{
Depth r = reduction(improving, depth, moveCount);
if (th.marked())
r++;
- // Decrease reduction if position is or has been on the PV (~10 Elo)
- if (ss->ttPv)
+ // Decrease reduction if position is or has been on the PV
+ // and node is not likely to fail low. (~10 Elo)
+ if ( ss->ttPv
+ && !likelyFailLow)
r -= 2;
// Increase reduction at root and non-PV nodes when the best move does not change frequently
- if ((rootNode || !PvNode) && thisThread->rootDepth > 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)
+ if ( moveCountPruning
+ && !formerPv)
r++;
// Decrease reduction if opponent's move count is high (~5 Elo)
if (captureOrPromotion)
{
- // Unless giving check, this capture is likely bad
+ // Increase reduction for non-checking captures likely to be bad
if ( !givesCheck
&& ss->staticEval + PieceValue[EG][pos.captured_piece()] + 210 * depth <= alpha)
r++;
// Decrease reduction for moves that escape a capture. Filter out
// castling moves, because they are coded as "king captures rook" and
- // hence break make_move(). (~2 Elo)
+ // hence break reverse_move() (~2 Elo)
else if ( type_of(move) == NORMAL
&& !pos.see_ge(reverse_move(move)))
r -= 2 + ss->ttPv - (type_of(movedPiece) == PAWN);
+ (*contHist[0])[movedPiece][to_sq(move)]
+ (*contHist[1])[movedPiece][to_sq(move)]
+ (*contHist[3])[movedPiece][to_sq(move)]
- - 5287;
+ - 4741;
// Decrease/increase reduction by comparing opponent's stat score (~10 Elo)
- if (ss->statScore >= -105 && (ss-1)->statScore < -103)
+ if (ss->statScore >= -89 && (ss-1)->statScore < -116)
r--;
- else if ((ss-1)->statScore >= -122 && ss->statScore < -129)
+ else if ((ss-1)->statScore >= -112 && ss->statScore < -100)
r++;
// Decrease/increase reduction for moves with a good/bad history (~30 Elo)
- // If we are not in check use statScore, if we are in check
- // use sum of main history and first continuation history with an offset
+ // If we are not in check use statScore, but if we are in check we use
+ // the sum of main history and first continuation history with an offset.
if (ss->inCheck)
r -= (thisThread->mainHistory[us][from_to(move)]
- + (*contHist[0])[movedPiece][to_sq(move)] - 4333) / 16384;
+ + (*contHist[0])[movedPiece][to_sq(move)] - 3833) / 16384;
else
- r -= ss->statScore / 14884;
+ r -= ss->statScore / 14790;
}
- Depth d = std::clamp(newDepth - r, 1, newDepth);
+ // In general we want to cap the LMR depth search at newDepth. But for nodes
+ // close to the principal variation the cap is at (newDepth + 1), which will
+ // allow these nodes to be searched deeper than the pv (up to 4 plies deeper).
+ Depth d = std::clamp(newDepth - r, 1, newDepth + ((ss+1)->distanceFromPv <= 4));
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
- doFullDepthSearch = value > alpha && d != newDepth;
-
+ // If the son is reduced and fails high it will be re-searched at full depth
+ doFullDepthSearch = value > alpha && d < newDepth;
didLMR = true;
}
else
{
doFullDepthSearch = !PvNode || moveCount > 1;
-
didLMR = false;
}
- // Step 16. Full depth search when LMR is skipped or fails high
+ // Step 17. Full depth search when LMR is skipped or fails high
if (doFullDepthSearch)
{
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, !cutNode);
std::min(maxNextDepth, newDepth), false);
}
- // Step 17. Undo move
+ // Step 18. Undo move
pos.undo_move(move);
assert(value > -VALUE_INFINITE && value < VALUE_INFINITE);
- // Step 18. Check for a new best move
+ // Step 19. Check for a new best move
// Finished searching the move. If a stop occurred, the return value of
// the search cannot be trusted, and we return immediately without
// updating best move, PV and TT.
return VALUE_DRAW;
*/
- // Step 19. Check for mate and stalemate
+ // Step 20. Check for mate and stalemate
// All legal moves have been searched and if there are no legal moves, it
// must be a mate or a stalemate. If we are in a singular extension search then
// return a fail low score.
assert(moveCount || !ss->inCheck || excludedMove || !MoveList<LEGAL>(pos).size());
if (!moveCount)
- bestValue = excludedMove ? alpha
- : ss->inCheck ? mated_in(ss->ply) : VALUE_DRAW;
+ 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)
moveCount++;
- // Futility pruning
+ // Futility pruning and moveCount pruning
if ( bestValue > VALUE_TB_LOSS_IN_MAX_PLY
&& !givesCheck
&& futilityBase > -VALUE_KNOWN_WIN
- && !pos.advanced_pawn_push(move))
+ && type_of(move) != PROMOTION)
{
- assert(type_of(move) != EN_PASSANT); // Due to !pos.advanced_pawn_push
- // moveCount pruning
if (moveCount > 2)
continue;
PieceType captured = type_of(pos.piece_on(to_sq(bestMove)));
bonus1 = stat_bonus(depth + 1);
- bonus2 = bestValue > beta + PawnValueMg ? bonus1 // larger bonus
- : stat_bonus(depth); // smaller bonus
+ bonus2 = bestValue > beta + PawnValueMg ? bonus1 // larger bonus
+ : std::min(bonus1, stat_bonus(depth)); // smaller bonus
if (!pos.capture_or_promotion(bestMove))
{
m.tbRank = 0;
}
}
+
+} // namespace Stockfish
projects / stockfish / blobdiff