// Step 8. Null move search with verification search (is omitted in PV nodes)
if ( !PvNode
&& eval >= beta
- && ss->staticEval >= beta - 36 * depth / ONE_PLY + 225)
+ && ss->staticEval >= beta - 36 * depth / ONE_PLY + 225
+ && (ss->ply >= thisThread->nmp_ply || ss->ply % 2 == thisThread->pair))
{
assert(eval - beta >= 0);
return nullValue;
// Do verification search at high depths
+ R += ONE_PLY;
+ // disable null move pruning for side to move for the first part of the remaining search tree
+ int nmp_ply = thisThread->nmp_ply;
+ int pair = thisThread->pair;
+ thisThread->nmp_ply = ss->ply + 3 * (depth-R) / 4;
+ thisThread->pair = (ss->ply % 2) == 0;
+
Value v = depth-R < ONE_PLY ? qsearch<NonPV, false>(pos, ss, beta-1, beta)
: search<NonPV>(pos, ss, beta-1, beta, depth-R, false, true);
+ thisThread->pair = pair;
+ thisThread->nmp_ply = nmp_ply;
if (v >= beta)
return nullValue;
th->rootDepth = th->completedDepth = DEPTH_ZERO;
th->rootMoves = rootMoves;
th->rootPos.set(pos.fen(), pos.is_chess960(), &setupStates->back(), th);
+ th->nmp_ply = 0;
+ th->pair = -1;
}
setupStates->back() = tmp;
Material::Table materialTable;
Endgames endgames;
size_t PVIdx;
- int selDepth;
+ int selDepth, nmp_ply, pair;
std::atomic<uint64_t> nodes, tbHits;
Position rootPos;