Fix a condition in connected_moves()

When checking if the moving piece p1 in a previous
move m1 defends the destination square of a move m2
we have to use the occupancy with the from square of
m2 removed so to take in account the case in which
f2 will block an x-ray attack from p1.

For instance in this position:
r2k3r/p1pp1pb1/qn3np1/1N2P3/1p3P2/2B5/PPP3QP/R3K2R b KQ - 1 9

The move eXf6 is connected to the previous move Bc3 that
defends the destination square f6.

With this patch we have about 10% more moves detected as
'connected'. Anyhow the absolute number is very low, about
4000 more moves out of 6M nodes searched.

Another issue spotted by Hongzhi "Hawk Eye" Cheng ;-)

new bench: 5757373
Fix an off-by-one bug in multi pv print

We send to GUI multi-pv info after each cycle,
not just once at the end of the PV loop. This is
because at high depths a single root search can
be very slow and we want to update the gui as
soon as we have a new PV score.

Idea is good but implementation is broken because
sort() takes as arguments a pointer to the first
element and one past the last element.

So fix the bug and rename sort arguments to better
reflect their meaning.

Another hit by Hongzhi Cheng.  Impressive!

No functional change.
Reformat connected_moves()

Prepare code for the next patch that
will affect functionality.

No functional change.
Relax constrain in connected_moves()

When testing if a piece is moving through the squares
vacated by a previous move there is no reason to require
the piece to be a slider, indeed we can have a double
pawn push like in this example:

r1q2rk1/2p1bppp/2Pp4/pN5b/Q1P1p3/4B2P/PP1R1PP1/1K5R w - - 3 18

Where black's move f5 is connected to previous move Be7 that
frees the path.

Or we can have a castle move:

r1bqkb1r/pppp1ppp/2n1pn2/1B6/4P3/2N2N2/PPPP1PPP/R1BQK2R b KQkq - 5 1

Where a previous move Bb5 allows the white to castle king side.

This time patch is mine ;-)

new bench: 5809010
Remove a redundant condition in connected_moves()

If a previous move attacks the king (with the piece
of the threat move removed) then must be a discovered
check, otherwise it means that first move gave check
and we were not able to do a null move.

Also renamed stuff to better document the function's
context.

No functional change.
Don't 'break' upon returning from split()

There is no guarantee that split() consumes all the node's
moves. Indeed split() can return without performing any job
for instance because MAX_SPLITPOINTS_PER_THREAD is reached
or becuase no available threads are found (this latter case
is much more common).

So search must continue in those cases and we cannot force
exiting from move's loop.

Bug introduced by 1ac417edb845 of 5/10/2012

Spotted by Frank Genot.

No functional change.
Sync connected_threat() and yields_to_threat()

Rename stuff so to sync as much as posisble the
two related functions.

No functional change.
Relax constrain in prevents_threat()

When testing if a move blocks the threat path there is no
reason to require the threat to be a slider. Indeed threat
can be a double pawn push like in this example:

r1bq1rk1/ppp1np1p/4n1p1/3p4/3P2Q1/2P1B3/PPBN2PP/R4RK1 w - - 0 16

Where white's move Rf6 blocks the threat f5.

As a nice side effect we can retire the now useless helper
piece_is_slider().

This patch kicks in only very rare cases, indeed the bench is
still the same!

bench: 5809010
Correctly fix "break from split" patch

In case split cut-offs we return with still
some moves to go but we really want to break
out from the loop now.

No functional change.
Skip evaluate() call after a null move

Reuse the evaluation of the parent with inverted sign and
set margin to zero (this is an hack!).

This is done only in qsearch where almost 15% of calls are
from a null move. In normal search the number of nodes where

(ss-1)->currentMove == MOVE_NULL

is almost zero and so there is no need of using this trick.

The big advantage of this patch is a speed-up due to skipped
evaluate() calls, that are very costly.

Functionality is of course affected and we will need to proper
test it later. For now we just register a 3-4% speed up.

Suggested by Hongzhi Cheng.

bench: 5051328
Temporary revert previous patch

Performs well at very short TC of 40/4+0.05 (courtesy of Jean-Francois):
Wins: 2503 Losses: 2146 Draws: 5581 Total: 10230 +12 ELO

But is poor at longer TC of 20"+0.05
Wins: 321 Losses: 373 Draws: 1141 Total: 1808 -10 ELO

The patch was clearly a tradoff between speed and accuracy and
the most interesting part of it are test results that can be
commented as follows:

- A short TC is very sensible to any speed increase
- A longer TC is more sensible to accuracy and less to speed

So a patch that does not change speed is suitable to be tested at
short TC, while a speed/accuracy compromise patch is IMO better to
be tested at longer TC to verify loss of accuracy can be tolerated.

In this case the revert is only temporary. We will come back again
once we will be able to preserve the evaluation margin.

bench: 5809010
Another attempt at evaluation shortcut

In this case we try a rather drastic
approach: we simply don't futility prune
in qsearch when arriving from a null move.

So we save evaluating and also save to mess
with eval margins at all because margin is used
only in futility.

Also accuracy should not be affected, actually it
improves because we don't prune anything anymore.

bench: 5404066
Previous patch test results

From Jean-Francois's

Final result after 5000 games :
Score of c581b7e vs a878312: 1163 - 970 - 2867 [0.519] 5000
ELO: 13.35 +- 99%: 12.71 95%: 9.65
LOS: 100.00%
Wins: 1163 Losses: 970 Draws: 2867 Total: 5000

From me

After 3266 games at 20"+0,05
Score of c581b7e vs a878312: 612 - 607 - 2047

So no regression at longer TC and perhaps a little gain at
fast TC.
Don't prune discovered checks

Don't prune and eventually extend check moves of type
DISCO_CHECK (pun intended, Lucas will understand :-) ).

Patch from Lucas Braesch that has also tested it:

Result: 879-661-2137, score=52.96%, LOS=100.00% (time 10"+0.1")

I have started a verification test right now.

bench: 6004966
Revert "Don't prune discovered checks"

Both Lucas re-test and Jean-Francois confirrm it
is a regression.

Here Jean-Francois's results after 3600 games :
Score of 96d3b1c92b8 vs 3b87314: 690 - 729 - 2181 [0.495] 3600
ELO: -3.86 +- 99%: 14.94 95%: 11.35
LOS: 15.03%
Wins: 690 Losses: 729 Draws: 2181 Total: 3600

Bench: 5404066
Restore old BOUND_EXACT logic in qsearch

In case a PvNode node has a static evaluation above alpha but
no available moves we want to flag the node as BOUND_EXACT,
not as BOUND_UPPER as is currently.

The behaviour was recently introduced with patch d471c49700fbe8281
of 3/10/2012

Spotted by Hongzhi Cheng.

bench: 5558464
Don't access std::cout from Position::print()

Let the caller to decide where to redirect (cout or cerr) the
ASCII representation of the position. Rename the function to
reflect this.

Renamed also from_fen() and to_fen() to set() and fen() respectively.

No functional change.
Better document fail-high condition

At this point we have already verified (value > alpha)
and this implies, in case of a non-PV node, where search
window size is zero, that value >= beta.

This is not so self-evident, so document the code with
an assert condition.

No functional change.
Triviality in move_gives_check()

It seems even a bit faster, although handling of the special
cases is not the hot path.

No functional change.
Avoid spamming the GUI in multipv search

Send the PV lines to GUI only once at the end of the
PV search loop or just in case of long searches.

We need to sync also sending of "currmove" info to
avoid sending info on current move without first
informing the GUI on the PV line we are searching on.

No functional change.