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Avoid search tree explosion in qsearch

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Under some rare cases we can have a search tree explosion
due to a perpetual check or to a very long non-capture TT
sequence.

This avoids the tree explosion not following TT moves that
are not captures or promotions when we are below the
'generate checks' depth.

Idea suggested by Richard Vida.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2010-01-29 16:47:04 +01:00
parent b651e5334b
commit 252844e899
1 changed files with 8 additions and 0 deletions
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8
src/movepick.cpp
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@ -94,8 +94,16 @@ MovePicker::MovePicker(const Position& p, Move ttm, Depth d,
else if (d == Depth(0))
phasePtr = QsearchWithChecksPhaseTable;
else
{
phasePtr = QsearchWithoutChecksPhaseTable;
// Skip TT move if is not a capture or a promotion, this avoids
// qsearch tree explosion due to a possible perpetual check or
// similar rare cases when TT table is full.
if (ttm != MOVE_NONE && !pos.move_is_capture_or_promotion(ttm))
searchTT = ttMoves[0].move = MOVE_NONE;
}
phasePtr += !searchTT - 1;
go_next_phase();
}