// Different node types, used as a template parameter
enum NodeType { NonPV, PV, Root };
- constexpr uint64_t TtHitAverageWindow = 4096;
- constexpr uint64_t TtHitAverageResolution = 1024;
-
// Futility margin
Value futility_margin(Depth d, bool improving) {
return Value(214 * (d - improving));
return VALUE_DRAW + Value(2 * (thisThread->nodes & 1) - 1);
}
+ // Check if the current thread is in a search explosion
+ ExplosionState search_explosion(Thread* thisThread) {
+
+ uint64_t nodesNow = thisThread->nodes;
+ bool explosive = thisThread->doubleExtensionAverage[WHITE].is_greater(2, 100)
+ || thisThread->doubleExtensionAverage[BLACK].is_greater(2, 100);
+
+ if (explosive)
+ thisThread->nodesLastExplosive = nodesNow;
+ else
+ thisThread->nodesLastNormal = nodesNow;
+
+ if ( explosive
+ && thisThread->state == EXPLOSION_NONE
+ && nodesNow - thisThread->nodesLastNormal > 6000000)
+ thisThread->state = MUST_CALM_DOWN;
+
+ if ( thisThread->state == MUST_CALM_DOWN
+ && nodesNow - thisThread->nodesLastExplosive > 6000000)
+ thisThread->state = EXPLOSION_NONE;
+
+ return thisThread->state;
+ }
+
// Skill structure is used to implement strength limit
struct Skill {
explicit Skill(int l) : level(l) {}
multiPV = std::max(multiPV, (size_t)4);
multiPV = std::min(multiPV, rootMoves.size());
- ttHitAverage = TtHitAverageWindow * TtHitAverageResolution / 2;
+ ttHitAverage.set(50, 100); // initialize the running average at 50%
+ doubleExtensionAverage[WHITE].set(0, 100); // initialize the running average at 0%
+ doubleExtensionAverage[BLACK].set(0, 100); // initialize the running average at 0%
+
+ nodesLastExplosive = nodes;
+ nodesLastNormal = nodes;
+ state = EXPLOSION_NONE;
trend = SCORE_ZERO;
int searchAgainCounter = 0;
template <NodeType nodeType>
Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
+ Thread* thisThread = pos.this_thread();
+
+ // Step 0. Limit search explosion
+ if ( ss->ply > 10
+ && search_explosion(thisThread) == MUST_CALM_DOWN
+ && depth > (ss-1)->depth)
+ depth = (ss-1)->depth;
+
constexpr bool PvNode = nodeType != NonPV;
constexpr bool rootNode = nodeType == Root;
const Depth maxNextDepth = rootNode ? depth : depth + 1;
Value bestValue, value, ttValue, eval, maxValue, probCutBeta;
bool givesCheck, improving, didLMR, priorCapture;
bool captureOrPromotion, doFullDepthSearch, moveCountPruning,
- ttCapture, singularQuietLMR;
+ ttCapture, singularQuietLMR, noLMRExtension;
Piece movedPiece;
int moveCount, captureCount, quietCount;
// Step 1. Initialize node
- Thread* thisThread = pos.this_thread();
ss->inCheck = pos.checkers();
priorCapture = pos.captured_piece();
Color us = pos.side_to_move();
(ss+1)->excludedMove = bestMove = MOVE_NONE;
(ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
ss->doubleExtensions = (ss-1)->doubleExtensions;
+ ss->depth = depth;
Square prevSq = to_sq((ss-1)->currentMove);
+ // Update the running average statistics for double extensions
+ thisThread->doubleExtensionAverage[us].update(ss->depth > (ss-1)->depth);
+
// Initialize statScore to zero for the grandchildren of the current position.
// So statScore is shared between all grandchildren and only the first grandchild
// starts with statScore = 0. Later grandchildren start with the last calculated
&& is_ok((ss-1)->currentMove))
thisThread->lowPlyHistory[ss->ply - 1][from_to((ss-1)->currentMove)] << stat_bonus(depth - 5);
- // thisThread->ttHitAverage can be used to approximate the running average of ttHit
- thisThread->ttHitAverage = (TtHitAverageWindow - 1) * thisThread->ttHitAverage / TtHitAverageWindow
- + TtHitAverageResolution * ss->ttHit;
+ // running average of ttHit
+ thisThread->ttHitAverage.update(ss->ttHit);
// At non-PV nodes we check for an early TT cutoff
if ( !PvNode
ss->ply);
value = bestValue;
- singularQuietLMR = moveCountPruning = false;
- bool doubleExtension = false;
+ singularQuietLMR = moveCountPruning = noLMRExtension = false;
// Indicate PvNodes that will probably fail low if the node was searched
// at a depth equal or greater than the current depth, and the result of this search was a fail low.
extension = 1;
singularQuietLMR = !ttCapture;
- // Avoid search explosion by limiting the number of double extensions to at most 3
+ // Avoid search explosion by limiting the number of double extensions
if ( !PvNode
&& value < singularBeta - 93
&& ss->doubleExtensions < 3)
{
extension = 2;
- doubleExtension = true;
+ noLMRExtension = true;
}
}
r--;
// Decrease reduction if the ttHit running average is large (~0 Elo)
- if (thisThread->ttHitAverage > 537 * TtHitAverageResolution * TtHitAverageWindow / 1024)
+ if (thisThread->ttHitAverage.is_greater(537, 1024))
r--;
// Decrease reduction if position is or has been on the PV
// In general we want to cap the LMR depth search at newDepth. But if
// reductions are really negative and movecount is low, we allow this move
- // to be searched deeper than the first move in specific cases.
- Depth d = std::clamp(newDepth - r, 1, newDepth + (r < -1 && (moveCount <= 5 || (depth > 6 && PvNode)) && !doubleExtension));
+ // to be searched deeper than the first move in specific cases (note that
+ // this may lead to hidden double extensions if newDepth got it own extension
+ // before).
+ int deeper = r >= -1 ? 0
+ : noLMRExtension ? 0
+ : moveCount <= 5 ? 1
+ : (depth > 6 && PvNode) ? 1
+ : 0;
+
+ Depth d = std::clamp(newDepth - r, 1, newDepth + deeper);
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
projects / stockfish / blobdiff