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Do more reductions for late quiet moves in case of consecutive fail highs. #3184

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Do more reductions for late quiet moves in case of consecutive fail highs. #3184

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24 changes: 13 additions & 11 deletions src/search.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -145,7 +145,7 @@ namespace {
};

template <NodeType NT>
Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode);
Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, int failedHighCnt, bool cutNode);

template <NodeType NT>
Value qsearch(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth = 0);
Expand Down Expand Up @@ -421,7 +421,7 @@ void Thread::search() {
while (true)
{
Depth adjustedDepth = std::max(1, rootDepth - failedHighCnt - searchAgainCounter);
bestValue = ::search<PV>(rootPos, ss, alpha, beta, adjustedDepth, false);
bestValue = ::search<PV>(rootPos, ss, alpha, beta, adjustedDepth, failedHighCnt, 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
Expand Down Expand Up @@ -561,7 +561,7 @@ namespace {
// search<>() is the main search function for both PV and non-PV nodes

template <NodeType NT>
Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, bool cutNode) {
Value search(Position& pos, Stack* ss, Value alpha, Value beta, Depth depth, int failedHighCnt, bool cutNode) {

constexpr bool PvNode = NT == PV;
const bool rootNode = PvNode && ss->ply == 0;
Expand Down Expand Up @@ -836,7 +836,7 @@ namespace {

pos.do_null_move(st);

Value nullValue = -search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, !cutNode);
Value nullValue = -search<NonPV>(pos, ss+1, -beta, -beta+1, depth-R, 0, !cutNode);

pos.undo_null_move();

Expand All @@ -856,7 +856,7 @@ namespace {
thisThread->nmpMinPly = ss->ply + 3 * (depth-R) / 4;
thisThread->nmpColor = us;

Value v = search<NonPV>(pos, ss, beta-1, beta, depth-R, false);
Value v = search<NonPV>(pos, ss, beta-1, beta, depth-R, 0, false);

thisThread->nmpMinPly = 0;

Expand Down Expand Up @@ -921,7 +921,7 @@ namespace {

// If the qsearch held, perform the regular search
if (value >= probCutBeta)
value = -search<NonPV>(pos, ss+1, -probCutBeta, -probCutBeta+1, depth - 4, !cutNode);
value = -search<NonPV>(pos, ss+1, -probCutBeta, -probCutBeta+1, depth - 4, 0, !cutNode);

pos.undo_move(move);

Expand Down Expand Up @@ -1074,7 +1074,7 @@ namespace {
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);
value = search<NonPV>(pos, ss, singularBeta - 1, singularBeta, singularDepth, 0, cutNode);
ss->excludedMove = MOVE_NONE;

if (value < singularBeta)
Expand All @@ -1096,7 +1096,7 @@ namespace {
else if (ttValue >= beta)
{
ss->excludedMove = move;
value = search<NonPV>(pos, ss, beta - 1, beta, (depth + 3) / 2, cutNode);
value = search<NonPV>(pos, ss, beta - 1, beta, (depth + 3) / 2, 0, cutNode);
ss->excludedMove = MOVE_NONE;

if (value >= beta)
Expand Down Expand Up @@ -1177,6 +1177,8 @@ namespace {
if (ttCapture)
r++;

r += failedHighCnt * failedHighCnt * moveCount / 512;

// Increase reduction for cut nodes (~10 Elo)
if (cutNode)
r += 2;
Expand Down Expand Up @@ -1218,7 +1220,7 @@ namespace {

Depth d = std::clamp(newDepth - r, 1, newDepth);

value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, true);
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, d, 0, true);

doFullDepthSearch = value > alpha && d != newDepth;

Expand All @@ -1234,7 +1236,7 @@ namespace {
// 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);
value = -search<NonPV>(pos, ss+1, -(alpha+1), -alpha, newDepth, 0, !cutNode);

if (didLMR && !captureOrPromotion)
{
Expand All @@ -1256,7 +1258,7 @@ namespace {
(ss+1)->pv = pv;
(ss+1)->pv[0] = MOVE_NONE;

value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, false);
value = -search<PV>(pos, ss+1, -beta, -alpha, newDepth, 0, false);
}

// Step 18. Undo move
Expand Down