SEE (Static Exchange Evaluation) is a critical component, so we might
indulge some tricks to make it faster. Another pull request #2469 showed
some speedup by removing templates, this version uses Ronald de Man
(@syzygy1) SEE implementation which also unrolls the for loop by
suppressing the min_attacker() helper function and exits as soon as
the last swap is conclusive.
See Ronald de Man version there:
https://github.com/syzygy1/Cfish/blob/master/src/position.c
Patch testes against pull request #2469:
LLR: 2.95 (-2.94,2.94) {-1.00,3.00}
Total: 19365 W: 3771 L: 3634 D: 11960
Ptnml(0-2): 241, 1984, 5099, 2092, 255
http://tests.stockfishchess.org/tests/view/5e10eb135e5436dd91b27ba3
And since we are using new SPRT statistics, and that both pull requests
finished with less than 20000 games I also tested against master as
a speed-up:
LLR: 2.99 (-2.94,2.94) {-1.00,3.00}
Total: 18878 W: 3674 L: 3539 D: 11665
Ptnml(0-2): 193, 1999, 4966, 2019, 250
http://tests.stockfishchess.org/tests/view/5e10febf12ef906c8b388745
Non functional change
Run as a simplification
a) insures that pawn attacks are always included in the pawn span
(this "fixes" the case where some outpost or reachable outpost
bonus were awarded on squares controlled by enemy pawns).
b) compute the full span only if not "backward" or not "blocked".
By looking at "blocked" instead of "opposed", we get a nice simpli-
fication and the "new" outpost detection is almost identical, except
a few borderline cases on rank 4.
passed STC
http://tests.stockfishchess.org/tests/view/5d9950730ebc5902b6cefb90
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 79113 W: 17168 L: 17159 D: 44786
passed LTC
http://tests.stockfishchess.org/tests/view/5d99d14e0ebc5902b6cf0692
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 41286 W: 6819 L: 6731 D: 27736
See https://github.com/official-stockfish/Stockfish/pull/2348
bench: 3812891
Remove the RookOnPawn logic (for rook on rank 5 and above aligning with pawns
on same row or file) which was overlapping with a few other parameters.
Inspired by @31m059 interesting result hinting that a direct attack on pawns
instead of PseudoAttacks might work.
http://tests.stockfishchess.org/tests/view/5d89a7c70ebc595091801b8d
After a few attempts by me and @31m059, and some long STC greens but red LTC,
as a proof of concept I first tried a local SPSA at VSTC trying to tune related
rook psqt rows, and mainly some rook related stuff in evaluate.cpp.
Result was STC green, but still red LTC,
Finally a 100M fishtest SPSA at LTC proved successful both at STC and LTC.
All this was possible with the awesome fishtest contributors.
At some point, I had 850 workers on the last test !
Run as a simplification
STC
http://tests.stockfishchess.org/tests/view/5d8d68f40ebc590f3beaf171
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 7399 W: 1693 L: 1543 D: 4163
LTC
http://tests.stockfishchess.org/tests/view/5d8d70270ebc590f3beaf63c
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 41617 W: 6981 L: 6894 D: 27742
Closes https://github.com/official-stockfish/Stockfish/pull/2329
bench: 4037914
Non functional simplification when we find the passed pawns in pawn.cpp
and some code clean up. It also better follows the pattern "flag the pawn"
and "score the pawn".
-------------------------
The idea behind the third condition for candidate passed pawn is a little
bit difficult to visualize. Just for the record, the idea is the following:
Consider White e5 d4 against black e6. d4 can (in some endgames) push
to d5 and lever e6. Thanks to this sacrifice, or after d5xe6, we consider
e5 as "passed".
However:
- if White e5/d4 against black e6/c6: d4 cannot safely push to d5 since d5 is double attacked;
- if White e5/d4 against black e6/d5: d4 cannot safely push to d5 since it is occupied.
This is exactly what the following expression does:
```
&& (shift<Up>(support) & ~(theirPawns | dblAttackThem)))
```
--------------------------
http://tests.stockfishchess.org/tests/view/5d3325bb0ebc5925cf0e6e91
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 124666 W: 27586 L: 27669 D: 69411
Closes https://github.com/official-stockfish/Stockfish/pull/2255
No functional change
a) Reduce PSQT values along the long diagonals on non-central squares
and increase the LongDiagonal bonus accordingly. The effect is to penalise
bishops on the long diagonal which can not "see" the 2 central squares.
The "good" bishops still have more or less the same bonus as current master.
b) For a bishop on a central square, because of the "| s" term in the code,
the LongDiagonalBonus was always given. So while being there, remove the "| s"
and compensate the central Bishop PSQT accordingly.
Passed STC
LLR: 2.95 (-2.94,2.94) [0.00,4.00]
Total: 44498 W: 9658 L: 9323 D: 25517
http://tests.stockfishchess.org/tests/view/5b8992770ebc592cf2748942
Passed LTC
LLR: 2.95 (-2.94,2.94) [0.00,4.00]
Total: 63092 W: 10324 L: 9975 D: 42793
http://tests.stockfishchess.org/tests/view/5b89a17a0ebc592cf2748b59
Closes https://github.com/official-stockfish/Stockfish/pull/1760
bench: 4693901
Make sure each piece is not scored more than once as a passed pawn "hinderer",
by scoring only the blockers along the passed pawn path. Inspired by TCEC Game 29.
Passed STC as a simplification
http://tests.stockfishchess.org/tests/view/5b3016d00ebc5902b2e58552
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 75388 W: 16656 L: 16641 D: 42091
Passed LTC as a simplification
http://tests.stockfishchess.org/tests/view/5b302ed90ebc5902b2e587fc
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 49157 W: 8460 L: 8386 D: 32311
Current master was also counting the number of attacks along a passed pawn path,
which might be misleading:
a) a defender might be counted many times for the same pawn path. For example a
White rook on a1 attacking a black pawn on a7 would score the bonus * 6 but
would be probably better placed on a8
b) a defender might be counted on different pawn paths and might be overloaded. For
example a Ke4 or Qe4 against pawns on d6 and f6 would score the bonus * 6.
Counting each blocker or attacker only once is more complicated, and does not help
either: http://tests.stockfishchess.org/tests/view/5b2ff1cb0ebc5902b2e582b2
After this small simplification, there might be ways to increase the HinderPassedPawn
penalty.
Closes https://github.com/official-stockfish/Stockfish/pull/1661
Bench: 4520519
We can view the patch version as adding some "undermining bonus" for
level pawns, when the defending side can not easily avoid the exchange
by advancing her pawn.
• Case 1) White b2,c3, Black a3,b3:
Black is breaking through, b2 deserves a penalty
• Case 2) White b2,c3, Black a3,c4:
if b2xa3 then White ends up with a weak pawn on a3
and probably a weak pawn on c3 too.
In either case, White can still not safely play b2-b3 and make a
phalanx with c3, which is the essence of a backward pawn definition.
Passed STC in SPRT[0, 4]:
LLR: -2.96 (-2.94,2.94) [0.00,4.00]
Total: 131169 W: 26523 L: 26199 D: 78447
http://tests.stockfishchess.org/tests/view/5aefa4d50ebc5902a409a151
ELO 1.19 [-0.38,2.88] (95%)
Passed LTC in SPRT[-3, 1]:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 24824 W: 3732 L: 3617 D: 17475
http://tests.stockfishchess.org/tests/view/5af04d3f0ebc5902a88b2e55
ELO 1.27 [-1.21,3.70] (95%)
Closes https://github.com/official-stockfish/Stockfish/pull/1584
How to continue from there?
There were some promising tests a couple of months ago about adding
a lever condition for king danger in evaluate.cpp, maybe it would
be time to re-try this after all the recent changes in pawns.cpp
Bench: 4773882
Queen was recently excluded from the mobility area of friendly minor
pieces. Exclude queen also from the mobility area of friendly majors too.
Run as a simplification:
STC
http://tests.stockfishchess.org/tests/view/5ade396f0ebc59602d053742
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 46972 W: 9511 L: 9437 D: 28024
LTC
http://tests.stockfishchess.org/tests/view/5ade64b50ebc5949f20a24d3
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 66855 W: 10157 L: 10105 D: 46593
How to continue from there?
The mobilityArea is used in various places of the evaluation as a
soft proxy for "not attacked by the opponent pawns". Now that the
mobility area is getting smaller and smaller, it may be worth to
hunt for Elo gains by trying the more direct ~attackedBy[Them][PAWN]
instead of mobilityArea[Us] in these places.
Bench: 4650572
In master, we already remove the King from the mobility area of minor pieces
because the King simply stands in the way of other pieces, and since opponent
cannot capture the King, any piece which "protects" the King cannot recapture.
Similarly, this patch introduces the idea that it is rarely a need for a Queen
to be "protected" by a minor (unless it is attacked only by a Queen, in fact).
We used to have a LoosePiece bonus, and in a similar vein the Queen was excluded
from that penalty.
Idea came when reviewing an old game of Kholmov. He was a very good midgame
player, but in the opening his misplace his Queen (and won in the end :-) :
http://www.chessgames.com/perl/chessgame?gid=1134645
Both white queen moves 10.Qd3 and 13.Qb3 are in the way of some minor piece.
I would prefer to not give a bishop mobility bonus at move 10 for the square d3,
or later a knight mobility bonus at move 13 for the square b3. And the textbook
move is 19.Qe3! which prepares 20.Nb3. This short game sample shows how much a
queen can be "in the way" of minor pieces.
STC
http://tests.stockfishchess.org/tests/view/5ac2c15f0ebc591746423fa3
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 22066 W: 4561 L: 4330 D: 13175
LTC
http://tests.stockfishchess.org/tests/view/5ac2d6500ebc591746423faf
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 25871 W: 3953 L: 3738 D: 18180
Closes https://github.com/official-stockfish/Stockfish/pull/1532
Ideas for future work in this area:
• tweak some more mobility areas for other piece type.
• construct a notion of global mobility for the whole piece set.
• bad bishops.
Bench: 4989125
Include some not fully supported levers in the (candidate) passed pawns
bitboard, if otherwise unblocked. Maybe levers are usually very short
lived, and some inaccuracy in the lever balance for the definition of
candidate passed pawns just triggers a deeper search.
Here is a example of a case where the patch has an effect on the definition
of candidate passers: White c5/e5 pawns, against Black d6 pawn. Let's say
we want to test if e5 is a candidate passer. The previous master looks
only at files d, e and f (which is already very good) and reject e5 as
a candidate. However, the lever d6 is challenged by 2 pawns, so it should
not fully count. Indirectly, this patch will view such case (and a few more)
to be scored as candidates.
STC
http://tests.stockfishchess.org/tests/view/5abcd55d0ebc5902926cf1e1
LLR: 2.95 (-2.94,2.94) [0.00,4.00]
Total: 16492 W: 3419 L: 3198 D: 9875
LTC
http://tests.stockfishchess.org/tests/view/5abce1360ebc5902926cf1e6
LLR: 2.95 (-2.94,2.94) [0.00,4.00]
Total: 21156 W: 3201 L: 2990 D: 14965
This was inspired by this test of Jerry Donald Watson, except the case of
zero supporting pawns against two levers is excluded, and it seems that
not excluding that case is bad, while excluding is it beneficial. See the
following tests on fishtest:
https://github.com/official-stockfish/Stockfish/pull/1519http://tests.stockfishchess.org/tests/view/5abccd850ebc5902926cf1ddhttp://tests.stockfishchess.org/tests/view/5abcdd490ebc5902926cf1e4
Closes https://github.com/official-stockfish/Stockfish/pull/1521
Bench: 5568461
----
Comments by Jerry Donald Watson:
> My thinking as to why this works:
>
> The evaluation is either called in an interior node or in the qsearch.
> The calls at the end of the qsearch are the more important as they
> ultimately determine the scoring of each move, whereas the internal
> values are mainly used for pruning decisions with a margin. Some strong
> engines don't even call the eval at all nodes. Now the whole point of
> the qsearch is to find quiet positions where captures do not change the
> evaluation of the position with regards to the search bounds - i.e. if
> there were good captures they would be tried.* So when a candidate lever
> appears in the evaluation at the end of the qsearch, the qsearch has
> guaranteed that it cannot just be captured, or if it can, this does not
> take the score past the search bounds. Practically this may mean that
> the side with the candidate lever has the turn, or perhaps the stopping
> lever pawn is pinned, or that side is forced for other reasons to make
> some other move (e.g. d6 can only take one of the pawns in the example
> above).
>
> Hence granting the full score for only one lever defender makes some
> sense, at least, to me.
>
> IMO this is also why huge bonuses for possible captures in the evaluation
> (e.g. threat on queen and our turn), etc. don't tend to work. Such things
> are best left to the search to figure out.
Allow a potential slider threat from a square currently occupied
by a harmless attacker, just as the recent "knight on queen" patch.
Also from not completely safe squares, use the mobilityArea instead
of excluding all pawns for both SlidersOnQueen and KnightOnQueen
We now compute the potential sliders threat on queen only if opponent
has one queen.
Run as SPRT [0,4] since it is some kind of simplification but maybe
not clearly one.
STC:
http://tests.stockfishchess.org/tests/view/5aa1ddf10ebc590297cb63d8
LLR: 2.95 (-2.94,2.94) [0.00,4.00]
Total: 22997 W: 4817 L: 4570 D: 13610
LTC:
http://tests.stockfishchess.org/tests/view/5aa1fe6b0ebc590297cb63e5
LLR: 2.95 (-2.94,2.94) [0.00,4.00]
Total: 11926 W: 1891 L: 1705 D: 8330
After this patch is committed, we may try to:
• re-introduce some "threat by queen" bonus to make Stockfish's queen
more aggressive (attacking aspect)
• introduce a concept of "queen overload" to force the opponent queen
into passivity and protecting duties (defensive aspect)
• more generally, re-tune the queen mobility array since patches in the
last three months have affected a lot the location/activity of queens.
Closes https://github.com/official-stockfish/Stockfish/pull/1473
bench: 5788691
Simplify the other check penalty computation. Compared to current master,
a) it uses a 143 kingDanger penalty instead of S(10, 10) for the "otherCheck"
(credits to ElbertoOne for finding a suitable kingDanger range to replace the score
and to Guardian for showing this could also be a neutral change at LTC).
This makes our king safety model more consistent and simpler.
b) it might also score more than one "otherCheck" penalty for a given piece type instead of just one
c) it might score many pinned penalties instead of just one.
d) It also remove 3 conditionals and uses simpler expressions.
So it was tested as a SPRT[-3, 1]
Passed STC
http://tests.stockfishchess.org/tests/view/5a2b560b0ebc590ccbb8ba6b
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 11705 W: 2217 L: 2080 D: 7408
And LTC
http://tests.stockfishchess.org/tests/view/5a2bfd0d0ebc590ccbb8bab0
LLR: 2.94 (-2.94,2.94) [-3.00,1.00]
Total: 26812 W: 3575 L: 3463 D: 19774
Trying to improve on b) another attempt was made to score also the
"otherchecks" for piece types which had some safe checks, but this
failed STC http://tests.stockfishchess.org/tests/view/5a2c79e60ebc590ccbb8badd
bench: 5149133
Move more code into eval_init, removing some
clutter in the main routine.
Write eval_init only from "our" point of view
(do not init the attackedBy[Them] bitboards).
Add mobilityArea to the evalinfo
A few edits while being there
tested for non-regression at STC
http://tests.stockfishchess.org/tests/view/587fab230ebc5915193f77d9
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 39585 W: 7183 L: 7094 D: 25308
Non functional change.
Non-functional changes
a) splitting the threat array to avoid using an enum
b) reorder the scores according to functions where they are used.
c) declarations in evaluate_pieces after the const(s) like elsewhere
d) more compact definitions of KingFlank,
now that we need it also for the PanwLessFlank penalty.
e) reuse CenterFiles in evaluate_space
f) move one line inside next popcount
No functional change.
Moving a few lines from evaluate_threats to evaluate_pieces allows to
a) Remove a condition pos.count<QUEEN>(Them) == 1
b) use precalculated s instead of pos.square(Them)
c) do not check the condition at all in queenless endings
Passed STC
http://tests.stockfishchess.org/tests/view/5752e0410ebc59029919b1f4
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 67175 W: 12194 L: 12152 D: 42829
and LTC
http://tests.stockfishchess.org/tests/view/57587b140ebc59029919b2f4
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 20276 W: 2774 L: 2653 D: 14849
bench: 7907962
Introducing a new multi-purpose penalty related to King safety, which
includes all kind of potential checks (from unsafe or unavailable
squares currently occupied by some other piece)
This will indirectly detect and reward some pins, discovered checks, and
motifs such as square vacation, or rook behind its pawn and aligned with
King (example Black Rg8, g7 against Kg1),
and penalize some pawn blockers (if they move, it allows a discovered
check by the pawn).
And since it looks also at protected squares, it detects some potential
defense overloading.
Finally, the rook contact checks had been removed some time ago. This
test will give a small bonus for them, as well as for bishop contact
checks.
Passed STC
http://tests.stockfishchess.org/tests/view/5729ec740ebc59301a354b36
LLR: 2.94 (-2.94,2.94) [0.00,5.00]
Total: 13306 W: 2477 L: 2296 D: 8533
and LTC
http://tests.stockfishchess.org/tests/view/572a5be00ebc59301a354b65
LLR: 2.97 (-2.94,2.94) [0.00,5.00]
Total: 20369 W: 2750 L: 2565 D: 15054
bench: 9298175
There was already a penalty for squares only defended by King (undefended)
This test records a penalty for completely undefended squares in the so called extended king-ring
(so if we exclude squares defended by a Kg8 for example, we only look at h6 g6 and f6)
We also exclude squares occupied by opponent pieces in this computation,
based on the following results
Was yellow at STC
LLR: -2.97 (-2.94,2.94) [0.00,5.00]
Total: 112499 W: 20649 L: 20293 D: 71557
and passed LTC
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 36805 W: 5100 L: 4857 D: 26848
Bench: 8430233
Resolves: #619
On top of the usual conditions
a) some opponent in front (but no lever)
b) some neighbours (in front) (but no neighbour behind or same rank)
c) < rank_5
to find out if a pawn is backward we look at the squares in front of this pawn to reach the same rank as the next neighbour.
In current master, a pawn is backward if any of those squares is controlled by an enemy pawn on an adjacent file
In this version, a pawn is ALSO backward if any of those squares is occupied by an enemy pawn.
STC:
http://tests.stockfishchess.org/tests/view/56fe7efd0ebc59301a3541f1
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 19051 W: 3557 L: 3433 D: 12061
LTC:
http://tests.stockfishchess.org/tests/view/56febc2d0ebc59301a354209
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 40810 W: 5619 L: 5526 D: 29665
Bench: 7525245
Resolves#614
Tuned the global mobility factor for each piece, as well as some +- delta,
The master mobility factor was {266,334} and tuning gave
{267, 362} +S(-2,-2) for the Knight
{249, 328} +S( 0,-2) for the Bishop
{298, 353} +S(1,1) for the Rook
{265, 358} +S(2,-1) for the Queen
Passed STC
LLR: 2.95 (-2.94,2.94) [0.00,4.00]
Total: 49402 W: 9367 L: 9037 D: 30998
and LTC
LLR: 2.97 (-2.94,2.94) [0.00,5.00]
Total: 26831 W: 3871 L: 3658 D: 19302
Bench: 8355485
Resolves#536
Using less parameters and code to compute Threats
Includes also a few spacing edits.
Run as a simplification.
Passed STC 10+0.1
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 18879 W: 3725 L: 3600 D: 11554
Passed LTC 60+0.4
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 74116 W: 11001 L: 10958 D: 52157
bench: 8004751
PawnSafePush, with the value S(5,5) proved not "necessary"
possibly due to recent changes to MobilityArea and other changes to Connected bonus.
STC:
LLR: 3.22 (-2.94,2.94) [-3.00,1.00]
Total: 98528 W: 18757 L: 18759 D: 61012
LTC:
LLR: 5.30 (-2.94,2.94) [-3.00,1.00]
Total: 204194 W: 31698 L: 31734 D: 140762
Bench: 7620871
Resolves#396
Based off of Pull request #383:
Include squares occupied by some pawns in the MobilityArea
a) not blocked
b) on rank 4 and above
c) or captures
Passed STC
LLR: 2.95 (-2.94,2.94) [-1.50,4.50]
Total: 8157 W: 1644 L: 1516 D: 4997
And LTC
LLR: 2.97 (-2.94,2.94) [0.00,6.00]
Total: 26086 W: 4274 L: 4051 D: 17761
-----------
Then, a simplification test failed, trying to remove b and c)
LLR: -2.95 (-2.94,2.94) [-3.00,1.00]
Total: 6048 W: 1117 L: 1288 D: 3643
Another simplification test, was run to remove just (c)
Passed STC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 28073 W: 5364 L: 5255 D: 17454
And LTC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 34652 W: 5448 L: 5348 D: 23856
A parameter tweak test showed that changing b) for "on rank 3 and above"
does not work
LLR: -2.95 (-2.94,2.94) [0.00,4.00]
Total: 5233 W: 937 L: 1077 D: 3219
Finally, a small rewrite, and we have this version
Include squares occupied by some pawns in the MobilityArea which are
a) not blocked
b) on rank 4 and above
Bench: 8977899
Resolves#385
In ei.attackedBy, Queen does not x-ray through Rook, but the Rook does
X-ray through the Queen.
So most of the rook contact checks supported by queen are, in fact,
Queen Contact Checks and they are already scored separately.
Bench: 7762189
Resolves#338
Small speed-up in pawn.cpp
Results for 10 tests for each version:
Base Test Diff
Mean 1435636 1445238 -9602
StDev 22576 23189 1848
p-value: 1
speedup: 0.007
No functional change
Resolves#295
