diff --git a/src/search.cpp b/src/search.cpp index fe9b446e..c8e6c8b6 100644 --- a/src/search.cpp +++ b/src/search.cpp @@ -943,13 +943,21 @@ moves_loop: // When in check, search starts from here && tte->depth() >= depth - 3 * ONE_PLY && pos.legal(move)) { - Value reducedBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE); + Value singularBeta = std::max(ttValue - 2 * depth / ONE_PLY, -VALUE_MATE); ss->excludedMove = move; - value = search(pos, ss, reducedBeta - 1, reducedBeta, depth / 2, cutNode); + value = search(pos, ss, singularBeta - 1, singularBeta, depth / 2, cutNode); ss->excludedMove = MOVE_NONE; - if (value < reducedBeta) + if (value < singularBeta) extension = ONE_PLY; + + // Multi-cut pruning + // Our ttMove is assumed to fail high, and now we failed high also on a reduced + // search without the ttMove. So we assume this expected Cut-node is not singular, + // that is multiple moves fail high, and we can prune the whole subtree by returning + // the hard beta bound. + else if (cutNode && singularBeta > beta) + return beta; } else if ( givesCheck // Check extension (~2 Elo) && pos.see_ge(move))