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Fix incorrect pruning in qsearch

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Only do countermove based pruning in qsearch if we already have a move with a better score than a TB loss.

This patch fixes a bug (started as 843a961) that incorrectly prunes moves if in check,
and adds an assert to make sure no wrong mate scores are given in the future.
It replaces a no-op moveCount check with a check for bestValue.

Initially discussed in #3171 and later in #3199, #3198 and #3210.
This PR effectively closes #3171
It also likely fixes #3196 where this causes user visible incorrect TB scores,
which probably result from these incorrect mate scores.

Passed STC and LTC non-regression tests.
https://tests.stockfishchess.org/tests/view/5f9ef8dabca9bf35bae7f648
LLR: 2.93 (-2.94,2.94) {-1.25,0.25}
Total: 21672 W: 2339 L: 2230 D: 17103
Ptnml(0-2): 126, 1689, 7083, 1826, 112

https://tests.stockfishchess.org/tests/view/5f9f0caebca9bf35bae7f666
LLR: 2.97 (-2.94,2.94) {-0.75,0.25}
Total: 33152 W: 1551 L: 1485 D: 30116
Ptnml(0-2): 27, 1308, 13832, 1390, 19

closes https://github.com/official-stockfish/Stockfish/pull/3214

Bench: 3625915
This commit is contained in:
J. Oster 2020-11-01 18:33:17 +01:00 • committed by Joost VandeVondele
parent 931070b65a
commit a260c9a8a2
1 changed files with 5 additions and 1 deletions
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6
src/search.cpp
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@ -1565,7 +1565,7 @@ moves_loop: // When in check, search starts from here
// CounterMove based pruning // CounterMove based pruning
if ( !captureOrPromotion if ( !captureOrPromotion
&& moveCount && bestValue > VALUE_TB_LOSS_IN_MAX_PLY
&& (*contHist[0])[pos.moved_piece(move)][to_sq(move)] < CounterMovePruneThreshold && (*contHist[0])[pos.moved_piece(move)][to_sq(move)] < CounterMovePruneThreshold
&& (*contHist[1])[pos.moved_piece(move)][to_sq(move)] < CounterMovePruneThreshold) && (*contHist[1])[pos.moved_piece(move)][to_sq(move)] < CounterMovePruneThreshold)
continue; continue;
@ -1600,7 +1600,11 @@ moves_loop: // When in check, search starts from here
// All legal moves have been searched. A special case: if we're in check // All legal moves have been searched. A special case: if we're in check
// and no legal moves were found, it is checkmate. // and no legal moves were found, it is checkmate.
if (ss->inCheck && bestValue == -VALUE_INFINITE) if (ss->inCheck && bestValue == -VALUE_INFINITE)
{
assert(!MoveList<LEGAL>(pos).size());
return mated_in(ss->ply); // Plies to mate from the root return mated_in(ss->ply); // Plies to mate from the root
}
tte->save(posKey, value_to_tt(bestValue, ss->ply), pvHit, tte->save(posKey, value_to_tt(bestValue, ss->ply), pvHit,
bestValue >= beta ? BOUND_LOWER : bestValue >= beta ? BOUND_LOWER :