assert(0 <= ss->ply && ss->ply < MAX_PLY);
- (ss+1)->ttPv = false;
+ (ss+1)->ttPv = false;
(ss+1)->excludedMove = bestMove = MOVE_NONE;
- (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
- Square prevSq = to_sq((ss-1)->currentMove);
+ (ss+2)->killers[0] = (ss+2)->killers[1] = MOVE_NONE;
+ ss->doubleExtensions = (ss-1)->doubleExtensions;
+ Square prevSq = to_sq((ss-1)->currentMove);
// Initialize statScore to zero for the grandchildren of the current position.
// So statScore is shared between all grandchildren and only the first grandchild
{
extension = 1;
singularQuietLMR = !ttCapture;
- if (!PvNode && value < singularBeta - 93)
+
+ // Avoid search explosion by limiting the number of double extensions to at most 3
+ if ( !PvNode
+ && value < singularBeta - 93
+ && ss->doubleExtensions < 3)
extension = 2;
}
// Add extension to new depth
newDepth += extension;
+ ss->doubleExtensions = (ss-1)->doubleExtensions + (extension == 2);
// Speculative prefetch as early as possible
prefetch(TT.first_entry(pos.key_after(move)));
// Initialize a MovePicker object for the current position, and prepare
// to search the moves. Because the depth is <= 0 here, only captures,
- // queen and checking knight promotions, and other checks(only if depth >= DEPTH_QS_CHECKS)
+ // queen promotions, and other checks (only if depth >= DEPTH_QS_CHECKS)
// will be generated.
MovePicker mp(pos, ttMove, depth, &thisThread->mainHistory,
&thisThread->captureHistory,