}
// History and stats update bonus, based on depth
-int stat_bonus(Depth d) { return std::min(357 * d - 483, 1511); }
+int stat_bonus(Depth d) { return std::min(291 * d - 350, 1200); }
+
+// History and stats update malus, based on depth
+int stat_malus(Depth d) { return std::min(361 * d - 361, 1182); }
// Add a small random component to draw evaluations to avoid 3-fold blindness
Value value_draw(const Thread* thisThread) {
beta = std::min(avg + delta, VALUE_INFINITE);
// Adjust optimism based on root move's averageScore (~4 Elo)
- optimism[us] = 103 * (avg + 33) / (std::abs(avg + 34) + 119);
- optimism[~us] = -116 * (avg + 40) / (std::abs(avg + 12) + 123);
+ optimism[us] = 110 * avg / (std::abs(avg) + 121);
+ optimism[~us] = -optimism[us];
// Start with a small aspiration window and, in the case of a fail
// high/low, re-search with a bigger window until we don't fail
// the previous ply (~0 Elo on STC, ~2 Elo on LTC).
if (prevSq != SQ_NONE && (ss - 1)->moveCount <= 2 && !priorCapture)
update_continuation_histories(ss - 1, pos.piece_on(prevSq), prevSq,
- -stat_bonus(depth + 1));
+ -stat_malus(depth + 1));
}
// Penalty for a quiet ttMove that fails low (~1 Elo)
else if (!ttCapture)
{
- int penalty = -stat_bonus(depth);
+ int penalty = -stat_malus(depth);
thisThread->mainHistory[us][from_to(ttMove)] << penalty;
update_continuation_histories(ss, pos.moved_piece(ttMove), to_sq(ttMove), penalty);
}
// Use static evaluation difference to improve quiet move ordering (~4 Elo)
if (is_ok((ss - 1)->currentMove) && !(ss - 1)->inCheck && !priorCapture)
{
- int bonus = std::clamp(-18 * int((ss - 1)->staticEval + ss->staticEval), -1812, 1812);
+ int bonus = std::clamp(-14 * int((ss - 1)->staticEval + ss->staticEval), -1449, 1449);
thisThread->mainHistory[~us][from_to((ss - 1)->currentMove)] << bonus;
+ if (type_of(pos.piece_on(prevSq)) != PAWN && type_of((ss - 1)->currentMove) != PROMOTION)
+ thisThread->pawnHistory[pawn_structure(pos)][pos.piece_on(prevSq)][prevSq] << bonus / 4;
}
// Set up the improving flag, which is true if current static evaluation is
if (depth <= 0)
return qsearch<PV>(pos, ss, alpha, beta);
- // For cutNodes without a ttMove, we decrease depth by 2
- // if current depth >= 8.
+ // For cutNodes without a ttMove, we decrease depth by 2 if depth is high enough.
if (cutNode && depth >= 8 && !ttMove)
depth -= 2;
{
assert(probCutBeta < VALUE_INFINITE);
- MovePicker mp(pos, ttMove, probCutBeta - ss->staticEval, &captureHistory,
- thisThread->pawnHistory);
+ MovePicker mp(pos, ttMove, probCutBeta - ss->staticEval, &captureHistory);
while ((move = mp.next_move()) != MOVE_NONE)
if (move != excludedMove && pos.legal(move))
prevSq != SQ_NONE ? thisThread->counterMoves[pos.piece_on(prevSq)][prevSq] : MOVE_NONE;
MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory, &captureHistory, contHist,
- thisThread->pawnHistory, countermove, ss->killers);
+ &thisThread->pawnHistory, countermove, ss->killers);
value = bestValue;
moveCountPruning = singularQuietLMR = false;
lmrDepth = std::max(lmrDepth, -1);
// Futility pruning: parent node (~13 Elo)
- if (!ss->inCheck && lmrDepth < 13 && ss->staticEval + 77 + 124 * lmrDepth <= alpha)
+ if (!ss->inCheck && lmrDepth < 13
+ && ss->staticEval + (bestValue < ss->staticEval - 62 ? 123 : 77)
+ + 127 * lmrDepth
+ <= alpha)
continue;
lmrDepth = std::max(lmrDepth, 0);
// Singular extension search (~94 Elo). If all moves but one fail low on a
// search of (alpha-s, beta-s), and just one fails high on (alpha, beta),
// then that move is singular and should be extended. To verify this we do
- // a reduced search on all the other moves but the ttMove and if the result
- // is lower than ttValue minus a margin, then we will extend the ttMove. Note
- // that depth margin and singularBeta margin are known for having non-linear
+ // a reduced search on the position excluding the ttMove and if the result
+ // is lower than ttValue minus a margin, then we will extend the ttMove.
+
+ // Note: the depth margin and singularBeta margin are known for having non-linear
// scaling. Their values are optimized to time controls of 180+1.8 and longer
- // so changing them requires tests at this type of time controls.
+ // so changing them requires tests at these types of time controls.
// Recursive singular search is avoided.
if (!rootNode && move == ttMove && !excludedMove
&& depth >= 4 - (thisThread->completedDepth > 24) + 2 * (PvNode && tte->is_pv())
&& tte->depth() >= depth - 3)
{
Value singularBeta = ttValue - (64 + 57 * (ss->ttPv && !PvNode)) * depth / 64;
- Depth singularDepth = (depth - 1) / 2;
+ Depth singularDepth = newDepth / 2;
ss->excludedMove = move;
value =
}
// Multi-cut pruning
- // Our ttMove is assumed to fail high, and now we failed high also on a
- // reduced search without the ttMove. So we assume this expected cut-node
- // is not singular, that multiple moves fail high, and we can prune the
- // whole subtree by returning a softbound.
+ // Our ttMove is assumed to fail high based on the bound of the TT entry,
+ // and if after excluding the ttMove with a reduced search we fail high over the original beta,
+ // we assume this expected cut-node is not singular (multiple moves fail high),
+ // and we can prune the whole subtree by returning a softbound.
else if (singularBeta >= beta)
return singularBeta;
- // If the eval of ttMove is greater than beta, reduce it (negative extension) (~7 Elo)
+ // Negative extensions
+ // If other moves failed high over (ttValue - margin) without the ttMove on a reduced search,
+ // but we cannot do multi-cut because (ttValue - margin) is lower than the original beta,
+ // we do not know if the ttMove is singular or can do a multi-cut,
+ // so we reduce the ttMove in favor of other moves based on some conditions:
+
+ // If the ttMove is assumed to fail high over current beta (~7 Elo)
else if (ttValue >= beta)
extension = -2 - !PvNode;
- // If we are on a cutNode, reduce it based on depth (negative extension) (~1 Elo)
+ // If we are on a cutNode but the ttMove is not assumed to fail high over current beta (~1 Elo)
else if (cutNode)
extension = depth < 19 ? -2 : -1;
- // If the eval of ttMove is less than value, reduce it (negative extension) (~1 Elo)
+ // If the ttMove is assumed to fail low over the value of the reduced search (~1 Elo)
else if (ttValue <= value)
extension = -1;
}
else if (PvNode && move == ttMove && move == ss->killers[0]
&& (*contHist[0])[movedPiece][to_sq(move)] >= 4194)
extension = 1;
+
+ // Recapture extensions (~1 Elo)
+ else if (PvNode && move == ttMove && to_sq(move) == prevSq
+ && captureHistory[movedPiece][to_sq(move)][type_of(pos.piece_on(to_sq(move)))]
+ > 4000)
+ extension = 1;
}
// Add extension to new depth
if ((ss + 1)->cutoffCnt > 3)
r++;
- // Decrease reduction for first generated move (ttMove)
+ // Set reduction to 0 for first picked move (ttMove) (~2 Elo)
+ // Nullifies all previous reduction adjustments to ttMove and leaves only history to do them
else if (move == ttMove)
- r--;
+ r = 0;
ss->statScore = 2 * thisThread->mainHistory[us][from_to(move)]
+ (*contHist[0])[movedPiece][to_sq(move)]
+ (*contHist[3])[movedPiece][to_sq(move)] - 3848;
// Decrease/increase reduction for moves with a good/bad history (~25 Elo)
- r -= ss->statScore / (10216 + 3855 * (depth > 5 && depth < 23));
+ r -= ss->statScore / 14200;
// Step 17. Late moves reduction / extension (LMR, ~117 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 >= 2 && moveCount > 1 + (PvNode && ss->ply <= 1)
+ if (depth >= 2 && moveCount > 1 + rootNode
&& (!ss->ttPv || !capture || (cutNode && (ss - 1)->moveCount > 1)))
{
// In general we want to cap the LMR depth search at newDepth, but when
// reduction is negative, we allow this move a limited search extension
// beyond the first move depth. This may lead to hidden double extensions.
- Depth d = std::clamp(newDepth - r, 1, newDepth + 1);
+ // To prevent problems when the max value is less than the min value,
+ // std::clamp has been replaced by a more robust implementation.
+ Depth d = std::max(1, std::min(newDepth - r, newDepth + 1));
value = -search<NonPV>(pos, ss + 1, -(alpha + 1), -alpha, d, true);
{
// Adjust full-depth search based on LMR results - if the result
// was good enough search deeper, if it was bad enough search shallower.
- const bool doDeeperSearch = value > (bestValue + 51 + 10 * (newDepth - d));
- const bool doEvenDeeperSearch = value > alpha + 700 && ss->doubleExtensions <= 6;
- const bool doShallowerSearch = value < bestValue + newDepth;
+ const bool doDeeperSearch = value > (bestValue + 50 + 2 * newDepth); // (~1 Elo)
+ const bool doShallowerSearch = value < bestValue + newDepth; // (~2 Elo)
- ss->doubleExtensions = ss->doubleExtensions + doEvenDeeperSearch;
-
- newDepth += doDeeperSearch - doShallowerSearch + doEvenDeeperSearch;
+ newDepth += doDeeperSearch - doShallowerSearch;
if (newDepth > d)
value = -search<NonPV>(pos, ss + 1, -(alpha + 1), -alpha, newDepth, !cutNode);
- int bonus = value <= alpha ? -stat_bonus(newDepth)
+ int bonus = value <= alpha ? -stat_malus(newDepth)
: value >= beta ? stat_bonus(newDepth)
: 0;
assert(0 <= ss->ply && ss->ply < MAX_PLY);
- // Decide whether or not to include checks: this fixes also the type of
- // TT entry depth that we are going to use. Note that in qsearch we use
- // only two types of depth in TT: DEPTH_QS_CHECKS or DEPTH_QS_NO_CHECKS.
+ // Decide the replacement and cutoff priority of the qsearch TT entries
ttDepth = ss->inCheck || depth >= DEPTH_QS_CHECKS ? DEPTH_QS_CHECKS : DEPTH_QS_NO_CHECKS;
// Step 3. Transposition table lookup
bestValue = ttValue;
}
else
- // In case of null move search use previous static eval with a different sign
+ // In case of null move search, use previous static eval with a different sign
ss->staticEval = bestValue =
(ss - 1)->currentMove != MOVE_NULL ? evaluate(pos) : -(ss - 1)->staticEval;
// will be generated.
Square prevSq = is_ok((ss - 1)->currentMove) ? to_sq((ss - 1)->currentMove) : SQ_NONE;
MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory, &thisThread->captureHistory,
- contHist, thisThread->pawnHistory, prevSq);
+ contHist, &thisThread->pawnHistory);
int quietCheckEvasions = 0;
PieceType captured;
int quietMoveBonus = stat_bonus(depth + 1);
+ int quietMoveMalus = stat_malus(depth);
if (!pos.capture_stage(bestMove))
{
thisThread->pawnHistory[pawn_structure(pos)][moved_piece][to_sq(bestMove)]
<< quietMoveBonus;
+ int moveMalus = bestValue > beta + 168 ? quietMoveMalus // larger malus
+ : stat_malus(depth); // smaller malus
+
// Decrease stats for all non-best quiet moves
for (int i = 0; i < quietCount; ++i)
{
thisThread->pawnHistory[pawn_structure(pos)][pos.moved_piece(quietsSearched[i])]
[to_sq(quietsSearched[i])]
- << -bestMoveBonus;
- thisThread->mainHistory[us][from_to(quietsSearched[i])] << -bestMoveBonus;
+ << -moveMalus;
+ thisThread->mainHistory[us][from_to(quietsSearched[i])] << -moveMalus;
update_continuation_histories(ss, pos.moved_piece(quietsSearched[i]),
- to_sq(quietsSearched[i]), -bestMoveBonus);
+ to_sq(quietsSearched[i]), -moveMalus);
}
}
else
&& ((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, -quietMoveBonus);
+ update_continuation_histories(ss - 1, pos.piece_on(prevSq), prevSq, -quietMoveMalus);
// Decrease stats for all non-best capture moves
for (int i = 0; i < captureCount; ++i)
{
moved_piece = pos.moved_piece(capturesSearched[i]);
captured = type_of(pos.piece_on(to_sq(capturesSearched[i])));
- captureHistory[moved_piece][to_sq(capturesSearched[i])][captured] << -quietMoveBonus;
+ captureHistory[moved_piece][to_sq(capturesSearched[i])][captured] << -quietMoveMalus;
}
}
}
-// Called in case we have no ponder move
-// before exiting the search, for instance, in case we stop the search during a
-// fail high at root. We try hard to have a ponder move to return to the GUI,
+// Called in case we have no ponder move before exiting the search,
+// for instance, in case we stop the search during a fail high at root.
+// We try hard to have a ponder move to return to the GUI,
// otherwise in case of 'ponder on' we have nothing to think about.
bool RootMove::extract_ponder_from_tt(Position& pos) {
projects / stockfish / blobdiff