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Add moves from failed high nodes in PV

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Considering only VALUE_TYPE_EXACT nodes is too
restrictive and has a number of side-effects, most
notably the truncation of PV line after a fail high
at root.

Note that in this way we are no more guaranteed that
PV line is built up with PV nodes only, because
it could happen that a side search overwrites with a
cut-off move a PV node and this cut-off move ends up
in PV.

Change should be almost not measurable, perhaps with
ponder on we could have some beneficial effect.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2010-07-10 11:55:56 +01:00
parent a47a7dadeb
commit 3703d12eb9
1 changed files with 5 additions and 8 deletions
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13
src/tt.cpp
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@ -176,11 +176,11 @@ void TranspositionTable::insert_pv(const Position& pos, Move pv[]) {
}
/// TranspositionTable::extract_pv() extends a PV by adding moves from the
/// transposition table at the end. This should ensure that the PV is almost
/// always at least two plies long, which is important, because otherwise we
/// will often get single-move PVs when the search stops while failing high,
/// and a single-move PV means that we don't have a ponder move.
/// TranspositionTable::extract_pv() builds a PV by adding moves from the
/// transposition table. We consider also failing high nodes and not only
/// VALUE_TYPE_EXACT nodes. This allow to always have a ponder move even
/// when we fail high at root and also a long PV to print that is important
/// for position analysis.
void TranspositionTable::extract_pv(const Position& pos, Move bestMove, Move pv[], const int PLY_MAX) {
@ -194,11 +194,8 @@ void TranspositionTable::extract_pv(const Position& pos, Move bestMove, Move pv[
pv[ply] = bestMove;
p.do_move(pv[ply++], st);
// Extract moves from TT when possible. We try hard to always
// get a ponder move, that's the reason of ply < 2 conditions.
while ( (tte = retrieve(p.get_key())) != NULL
&& tte->move() != MOVE_NONE
&& (tte->type() == VALUE_TYPE_EXACT || ply < 2)
&& move_is_legal(p, tte->move())
&& (!p.is_draw() || ply < 2)
&& ply < PLY_MAX)