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Introduce Quadruple Extensions #5211

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Introduce Quadruple Extensions #5211

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22 changes: 9 additions & 13 deletions src/search.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -593,7 +593,6 @@ Value Search::Worker::search(
bestMove = Move::none();
(ss + 2)->killers[0] = (ss + 2)->killers[1] = Move::none();
(ss + 2)->cutoffCnt = 0;
ss->multipleExtensions = (ss - 1)->multipleExtensions;
Square prevSq = ((ss - 1)->currentMove).is_ok() ? ((ss - 1)->currentMove).to_sq() : SQ_NONE;
ss->statScore = 0;

Expand Down Expand Up @@ -1049,17 +1048,15 @@ Value Search::Worker::search(

if (value < singularBeta)
{
extension = 1;

// We make sure to limit the extensions in some way to avoid a search explosion
if (!PvNode && ss->multipleExtensions <= 16)
{
extension = 2 + (value < singularBeta - 11 && !ttCapture);
depth += depth < 14;
}
if (PvNode && !ttCapture && ss->multipleExtensions <= 5
&& value < singularBeta - 38)
extension = 2;
int doubleMargin = 251 * PvNode - 241 * !ttCapture;
int tripleMargin = 135 + 234 * PvNode - 248 * !ttCapture + 124 * (ss->ttPv || !ttCapture);
int quadMargin = 447 + 354 * PvNode - 300 * !ttCapture + 206 * ss->ttPv;

extension = 1 + (value < singularBeta - doubleMargin)
+ (value < singularBeta - tripleMargin)
+ (value < singularBeta - quadMargin);

depth += ((!PvNode) && (depth < 14));
}

// Multi-cut pruning
Expand Down Expand Up @@ -1104,7 +1101,6 @@ Value Search::Worker::search(

// Add extension to new depth
newDepth += extension;
ss->multipleExtensions = (ss - 1)->multipleExtensions + (extension >= 2);

// Speculative prefetch as early as possible
prefetch(tt.first_entry(pos.key_after(move)));
Expand Down
1 change: 0 additions & 1 deletion src/search.h
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Original file line number Diff line number Diff line change
Expand Up @@ -74,7 +74,6 @@ struct Stack {
bool inCheck;
bool ttPv;
bool ttHit;
int multipleExtensions;
int cutoffCnt;
};

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