Bug fix merged from Glaurung 2.2 for search_pv()
Added the same fix also to sp_search_pv() where
was missing.
Signed-off-by: Marco Costalba <mcostalba@gmail.com>
Use a margin to compare with beta so that positions
that after the verifying qsearch have gained a lot of points
are not discarded just becasue not above beta.
Also remove the second condition on depth <= OnePly, it
was too risky and added only a 2% more of pruned nodes.
Signed-off-by: Marco Costalba <mcostalba@gmail.com>
Fix the logic in search_pv and sp_search_pv
An additional issue to consider is that a castle move
is not a capture but destination square is not empty.
Signed-off-by: Marco Costalba <mcostalba@gmail.com>
Instead of number of searched nodes use the number of
opponent beta-cutoff occurred under the move subtree.
After 570 games 1+0 we have: +150 =288 -132 (+11 ELO)
Signed-off-by: Marco Costalba <mcostalba@gmail.com>
When a null move fails low due to a capture, try
to detect if without the capture we are above beta,
in this case there is a good possibility this is
a cut-node and the capture is just a null move
artifact due to side to move change. So if we still
don't have a TT move it's a good time to start an IID.
Signed-off-by: Marco Costalba <mcostalba@gmail.com>
Null move can fail low because of a capture artifact due
to the side to move change. Try to detect this condition
and fail high instead.
This pruning is very powerful, around 7% of nodes, but is
still experimental so is disabled by default.
Set UseNullCapturePruning to true to enable.
Signed-off-by: Marco Costalba <mcostalba@gmail.com>
Strength increase was due to an hidden bug introduced
by the patch, namely the time per move to /30 instead
of /40 (see previous patch).
After testing this feature do not add any substantial
increase so is removed.
Signed-off-by: Marco Costalba <mcostalba@gmail.com>
Cleanup and document.
The real functional change is that not mate threat
moves are never pruned, as could happen before.
Signed-off-by: Marco Costalba <mcostalba@gmail.com>
We can have depth(0) also in problematic cases
according to how extensions are tweaked by the user.
In any case we don't want to prune these moves.
Signed-off-by: Marco Costalba <mcostalba@gmail.com>
Add infrastructure to threat killer moves as a vector,
this will allow us to easily parametrize the number of
killer moves, instead of hardcode this value to two as is now.
This patch just add the infrastructure, no functional
change.
Signed-off-by: Marco Costalba <mcostalba@gmail.com>
It is erroneusly considered a capture because king
moves on the same square of the rook.
Use the correct function Position::move_is_capture()
instead of the open coded (and buggy) one.
Signed-off-by: Marco Costalba <mcostalba@gmail.com>
Killers should not be captures, but checks are not
and are produced also in qsearch.
Use this information, will be useful for move ordering.
Signed-off-by: Marco Costalba <mcostalba@gmail.com>
Is set during the last iteration.
Sometime also during the second last.
During the last iteration is set in the 95% of cases.
During the second last is set in the 40% of cases.
Signed-off-by: Marco Costalba <mcostalba@gmail.com>
Allow a seacrh to take a bit more time if needed.
This reduces the chanches of wast all the search time
for the last iteration and also allow to start the last
iteration when we have less time remaining.
Signed-off-by: Marco Costalba <mcostalba@gmail.com>
It seems that "few moves" works because we extend the good
captures at the last ply of PV, so code it directly.
This version seems defenitly stronger then previous one.
Signed-off-by: Marco Costalba <mcostalba@gmail.com>
