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simplify see pruning in qsearch #5607

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simplify see pruning in qsearch #5607

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16 changes: 4 additions & 12 deletions src/search.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1592,19 +1592,11 @@ Value Search::Worker::qsearch(Position& pos, Stack* ss, Value alpha, Value beta)
continue;
}

// If static eval is much lower than alpha and move is
// not winning material, we can prune this move. (~2 Elo)
if (futilityBase <= alpha && !pos.see_ge(move, 1))
// if static exchange evaluation is low enough
// we can prune this move. (~2 Elo)
if (!pos.see_ge(move, alpha - futilityBase))
{
bestValue = std::max(bestValue, futilityBase);
continue;
}

// If static exchange evaluation is much worse than what
// is needed to not fall below alpha, we can prune this move.
if (futilityBase > alpha && !pos.see_ge(move, (alpha - futilityBase) * 4))
{
bestValue = alpha;
bestValue = (futilityBase > alpha) ? alpha : std::max(bestValue, futilityBase);
continue;
}
}
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