There is an ambiguity between global and std clamp implementations when compiling in c++17,
and on certain toolchains that are not strictly conforming to c++11.
This is solved by putting our clamp implementation in a namespace.
closes https://github.com/official-stockfish/Stockfish/pull/2572
No functional change.
In November 2019, as a result of the simplification of rank-based outposts by 37698b0,
separate bonuses were introduced for outposts that are currently occupied and outposts
that are reachable on the next move. However, the values of these two bonuses are
quite similar, and they have remained that way for three months of development.
It appears that we can safely retire the separate ReachableOutpost parameter and
use the same Outpost bonus in both cases, restoring the basic principles of Stockfish
outpost evaluation to their pre-November state, while also reducing
the size of the parameter space.
STC:
LLR: 2.96 (-2.94,2.94) {-1.50,0.50}
Total: 47680 W: 9213 L: 9092 D: 29375
Ptnml(0-2): 776, 5573, 11071, 5594, 826
https://tests.stockfishchess.org/tests/view/5e51e33190a0a02810d09802
LTC:
LLR: 2.94 (-2.94,2.94) {-1.50,0.50}
Total: 14690 W: 1960 L: 1854 D: 10876
Ptnml(0-2): 93, 1381, 4317, 1435, 119
https://tests.stockfishchess.org/tests/view/5e52197990a0a02810d0980f
closes https://github.com/official-stockfish/Stockfish/pull/2559
Bench: 4697493
Current move histories are known to work well near the leaves, whilst at
higher depths they aren't very helpful. To address this problem this
patch introduces a table dedicated for what's happening at plies 0-3.
It's structured like mainHistory with ply index instead of color.
It get cleared with each new search and is filled during iterative
deepening at higher depths when recording successful quiet moves near
the root or traversing nodes which were in the principal variation
(ttPv).
Medium TC (20+0.2):
https://tests.stockfishchess.org/tests/view/5e4d358790a0a02810d096dc
LLR: 2.94 (-2.94,2.94) {-0.50,1.50}
Total: 100910 W: 16682 L: 16376 D: 67852
Ptnml(0-2): 1177, 10983, 25883, 11181, 1231
LTC:
https://tests.stockfishchess.org/tests/view/5e4e2cb790a0a02810d09714
LLR: 2.95 (-2.94,2.94) {0.25,1.75}
Total: 80444 W: 10495 L: 10095 D: 59854
Ptnml(0-2): 551, 7479, 23803, 7797, 592
closes https://github.com/official-stockfish/Stockfish/pull/2557
Bench: 4705960
This is a patch that significantly improves playing KNNKP endgames:
```
Score of 2553 vs master: 132 - 38 - 830 [0.547] 1000
Elo difference: 32.8 +/- 8.7, LOS: 100.0 %, DrawRatio: 83.0 %
```
At the same time it reduces the evaluation of this mostly draw engame
from ~7.5 to ~1.5
This patch does not regress against master in normal games:
STC
LLR: 2.94 (-2.94,2.94) {-1.50,0.50}
Total: 96616 W: 18459 L: 18424 D: 59733
Ptnml(0-2): 1409, 10812, 23802, 10905, 1380
http://tests.stockfishchess.org/tests/view/5e49dfe6f8d1d52b40cd31bc
LTC
LLR: 2.95 (-2.94,2.94) {-1.50,0.50}
Total: 49726 W: 6340 L: 6304 D: 37082
Ptnml(0-2): 239, 4227, 15906, 4241, 250
http://tests.stockfishchess.org/tests/view/5e4ab9ee16fb3df8c4cc01d0
Theory: KNNK is a dead draw, however the presence of the additional weakSide pawn opens up some mate opportunities. The idea is to block the pawn (preferably behind the Troitsky line) with one of the knights and press the weakSide king into a corner. If we can stalemate the king, we release the pawn with the knight (to avoid actual stalemate), and use the knight to complete the mate before the pawn promotes. This is also why there is an additional penalty for advancement of the pawn.
closes https://github.com/official-stockfish/Stockfish/pull/2553
Bench: 4981770
Fixes#2533, fixes#2543, fixes#2423.
the code that prevents false mate announcements depending on the TT
state (GHI), incorrectly used VALUE_MATE_IN_MAX_PLY. The latter
constant, however, also includes, counterintuitively, the TB win range.
This patch fixes that, by restoring the behavior for TB win scores,
while retaining the false mate correctness, and improving the mate
finding ability. In particular
no alse mates are announced with the poisened hash testcase
```
position fen 8/8/8/3k4/8/8/6K1/7R w - - 0 1
go depth 40
position fen 8/8/8/3k4/8/8/6K1/7R w - - 76 1
go depth 20
ucinewgame
```
mates are found with the testcases reported in #2543
```
position fen 4k3/3pp3/8/8/8/8/2PPP3/4K3 w - - 0 1
setoption name Hash value 1024
go depth 55
ucinewgame
```
and
```
position fen 4k3/4p3/8/8/8/8/3PP3/4K3 w - - 0 1
setoption name Hash value 1024
go depth 45
ucinewgame
```
furthermore, on the mate finding benchmark (ChestUCI_23102018.epd),
performance improves over master, roughly reaching performance with the
false mate protection reverted
```
Analyzing 6566 mate positions for best and found mates:
----------------best ---------------found
nodes master revert fixed master revert fixed
16000000 4233 4236 4235 5200 5201 5199
32000000 4583 4585 4585 5417 5424 5418
64000000 4852 4853 4855 5575 5584 5579
128000000 5071 5068 5066 5710 5720 5716
256000000 5280 5282 5279 5819 5827 5826
512000000 5471 5468 5468 5919 5935 5932
```
On a testcase with TB enabled, progress is made consistently, contrary
to master
```
setoption name SyzygyPath value ../../../syzygy/3-4-5/
setoption name Hash value 2048
position fen 1R6/3k4/8/K2p4/4n3/2P5/8/8 w - - 0 1
go depth 58
ucinewgame
```
The PR (prior to a rewrite for clarity)
passed STC:
LLR: 2.94 (-2.94,2.94) {-1.50,0.50}
Total: 65405 W: 12454 L: 12384 D: 40567
Ptnml(0-2): 920, 7256, 16285, 7286, 944
http://tests.stockfishchess.org/tests/view/5e441a3be70d848499f63d15
passed LTC:
LLR: 2.94 (-2.94,2.94) {-1.50,0.50}
Total: 27096 W: 3477 L: 3413 D: 20206
Ptnml(0-2): 128, 2215, 8776, 2292, 122
http://tests.stockfishchess.org/tests/view/5e44e277e70d848499f63d63
The incorrectly named VALUE_MATE_IN_MAX_PLY and VALUE_MATED_IN_MAX_PLY
were renamed into VALUE_TB_WIN_IN_MAX_PLY and VALUE_TB_LOSS_IN_MAX_PLY,
and correclty defined VALUE_MATE_IN_MAX_PLY and VALUE_MATED_IN_MAX_PLY
were introduced.
One further (corner case) mistake using these constants was fixed (go
mate X), which could lead to a premature return if X > MAX_PLY / 2,
but TB were present.
Thanks to @svivanov72 for one of the reports and help fixing the issue.
closes https://github.com/official-stockfish/Stockfish/pull/2552
Bench: 4932981
Align the TT allocation by 2M to make it huge page friendly and advise the
kernel to use huge pages.
Benchmarks on my i7-8700K (6C/12T) box: (3 runs per bench per config)
vanilla (nps) hugepages (nps) avg
==================================================================================
bench | 3012490 3024364 3036331 3071052 3067544 3071052 +1.5%
bench 16 12 20 | 19237932 19050166 19085315 19266346 19207025 19548758 +1.1%
bench 16384 12 20 | 18182313 18371581 18336838 19381275 19738012 19620225 +7.0%
On my box, huge pages have a significant perf impact when using a big
hash size. They also speed up TT initialization big time:
vanilla (s) huge pages (s) speed-up
=======================================================================
time stockfish bench 16384 1 1 | 5.37 1.48 3.6x
In practice, huge pages with auto-defrag may always be enabled in the
system, in which case this patch has no effect. This
depends on the values in /sys/kernel/mm/transparent_hugepage/enabled
and /sys/kernel/mm/transparent_hugepage/defrag.
closes https://github.com/official-stockfish/Stockfish/pull/2463
No functional change
This patch greatly increases the endgame penalty for having a trapped rook.
Idea was a result of witnessing Stockfish losing some games at CCCC exchanging
pieces in the position with a trapped rook which directly lead to a lost endgame.
This patch should partially fix such behavior making this penalty high even in
deep endgames.
Passed STC
http://tests.stockfishchess.org/tests/view/5e279d7cc3b97aa0d75bc1c4
LLR: 2.94 (-2.94,2.94) {-1.00,3.00}
Total: 8528 W: 1706 L: 1588 D: 5234
Ptnml(0-2): 133, 957, 1985, 1024, 159
Passed LTC
http://tests.stockfishchess.org/tests/view/5e27aee4c3b97aa0d75bc1e1
LLR: 2.95 (-2.94,2.94) {0.00,2.00}
Total: 88713 W: 11520 L: 11130 D: 66063
Ptnml(0-2): 646, 8170, 26342, 8492, 676
Closes https://github.com/official-stockfish/Stockfish/pull/2510
Bench: 4964462
----------------------
Comment by Malcolm Campbell:
Congrats! I think this might be a common pattern - scores that seem to mainly apply
to the midgame are often better with a similar (or at least fairly big) endgame value
as well. Maybe there are others eval parameters we can tweak like this...
Currently on a normal bench run in ~0,7% of cases 'improving' is set to
true although the static eval isn't improving at all, just keeping
equal. It looks like the strict gt-operator is more appropriate here,
since it returns to 'improving' its literal meaning without sideffects.
STC {-1.00,3.00} failed yellow:
https://tests.stockfishchess.org/tests/view/5e1ec38c8fd5f550e4ae1c28
LLR: -2.93 (-2.94,2.94) {-1.00,3.00}
Total: 53155 W: 10170 L: 10109 D: 32876
Ptnml(0-2): 863, 6282, 12251, 6283, 892
non-regression LTC passed:
https://tests.stockfishchess.org/tests/view/5e1f1c0d8fd5f550e4ae1c41
LLR: 2.98 (-2.94,2.94) {-1.50,0.50}
Total: 23961 W: 3114 L: 3018 D: 17829
Ptnml(0-2): 163, 2220, 7114, 2298, 170
CLoses https://github.com/official-stockfish/Stockfish/pull/2496
bench: 4561386
This is a non-functional simplification. Looks like std::bitset works good
for the KPKBitbase. Thanks for Jorg Oster for helping get the speed up
(the [] accessor is faster than test()).
Speed testing: 10k calls to probe:
master 9.8 sec
patch 9.8 sec.
STC
LLR: 2.94 (-2.94,2.94) {-1.50,0.50}
Total: 100154 W: 19025 L: 18992 D: 62137
Ptnml(0-2): 1397, 11376, 24572, 11254, 1473
http://tests.stockfishchess.org/tests/view/5e21e601346e35ac603b7d2b
Closes https://github.com/official-stockfish/Stockfish/pull/2502
No functional change
This is a non-functional speed-up: master has to access SquareBB twice while this patch
determines opposite_colors just using the values of the squares. It doesn't seem to change
the overall speed of bench, but calling opposite_colors(...) 10 Million times:
master: 39.4 seconds
patch: 11.4 seconds.
The only data point I have (other than my own tests), is a quite old failed STC test:
LLR: -2.93 (-2.94,2.94) [-1.50,4.50]
Total: 24308 W: 5331 L: 5330 D: 13647
Ptnml(0-2): 315, 2577, 6326, 2623, 289
http://tests.stockfishchess.org/tests/view/5e010256c13ac2425c4a9a67
Closes https://github.com/official-stockfish/Stockfish/pull/2498
No functional change
This is a non-functional simplification. If we use the "side to move" of the entry
instead of the template, one of the classify methods goes away. Furthermore, I've
resolved the colors in some of the statements (we're already assuming direction
using NORTH), and used stm (side to move) instead of "us," since this is much clearer
to me.
This is not tested because it is non-functional, only applies building the bitbase
and there are no changes to the binary (on my machine).
Closes https://github.com/official-stockfish/Stockfish/pull/2485
No functional change
This is a non-functional simplification. Instead of passing the piece type
for remove_piece, we can rely on the board. The only exception is en-passant
which must be explicitly set because the destination square for the capture
is not the same as the piece to remove.
Verified also in the Chess960 castling case by running a couple of perft, see
the pull request discussion: https://github.com/official-stockfish/Stockfish/pull/2460
STC
LLR: 2.94 (-2.94,2.94) [-3.00,1.00]
Total: 18624 W: 4147 L: 4070 D: 10407
Ptnml(0-2): 223, 1933, 4945, 1938, 260
http://tests.stockfishchess.org/tests/view/5dfeaa93e70446e17e451163
No functional change
Official release version of Stockfish 11.
Bench: 5156767
-----------------------
It is our pleasure to release Stockfish 11 to our fans and supporters.
Downloads are freely available at http://stockfishchess.org/download/
This version 11 of Stockfish is 50 Elo stronger than the last version, and
150 Elo stronger than the version which famously lost a match to AlphaZero
two years ago. This makes Stockfish the strongest chess engine running on
your smartphone or normal desktop PC, and we estimate that on a modern four
cores CPU, Stockfish 11 could give 1:1000 time odds to the human chess champion
having classical time control, and be on par with him. More specific data,
including nice cumulative curves for the progression of Stockfish strength
over the last seven years, can be found on [our progression page][1], at
[Stefan Pohl site][2] or at [NextChessMove][3].
In October 2019 Stockfish has regained its crown in the TCEC competition,
beating in the superfinal of season 16 an evolution of the neural-network
engine Leela that had won the previous season. This clash of style between an
alpha-beta and an neural-network engine produced spectacular chess as always,
with Stockfish [emerging victorious this time][0].
Compared to Stockfish 10, we have made hundreds of improvements to the
[codebase][4], from the evaluation function (improvements in king attacks,
middlegame/endgame transitions, and many more) to the search algorithm (some
innovative coordination methods for the searching threads, better pruning of
unsound tactical lines, etc), and fixed a couple of bugs en passant.
Our testing framework [Fishtest][5] has also seen its share of improvements
to continue propelling Stockfish forward. Along with a lot of small enhancements,
Fishtest has switched to new SPRT bounds to increase the chance of catching Elo
gainers, along with a new testing book and the use of pentanomial statistics to
be more resource-efficient.
Overall the Stockfish project is an example of open-source at its best, as
its buzzing community of programmers sharing ideas and daily reviewing their
colleagues' patches proves to be an ideal form to develop innovative ideas for
chess programming, while the mathematical accuracy of the testing framework
allows us an unparalleled level of quality control for each patch we put in
the engine. If you wish, you too can help our ongoing efforts to keep improving
it, just [get involved][6] :-)
Stockfish is also special in that every chess fan, even if not a programmer,
[can easily help][7] the team to improve the engine by connecting their PC to
Fishtest and let it play some games in the background to test new patches.
Individual contributions vary from 1 to 32 cores, but this year Bojun Guo
made it a little bit special by plugging a whole data center during the whole
year: it was a vertiginous experience to see Fishtest spikes with 17466 cores
connected playing [25600 games/minute][8]. Thanks Guo!
The Stockfish team
[0]: <http://mytcecexperience.blogspot.com/2019/10/season-16-superfinal-games-91-100.html>
[1]: <https://github.com/glinscott/fishtest/wiki/Regression-Tests>
[2]: <https://www.sp-cc.de/index.htm>
[3]: <https://nextchessmove.com/dev-builds>
[4]: <https://github.com/official-stockfish/Stockfish>
[5]: <https://tests.stockfishchess.org/tests>
[6]: <https://stockfishchess.org/get-involved/>
[7]: <https://github.com/glinscott/fishtest/wiki>
[8]: <https://groups.google.com/forum/?fromgroups=#!topic/fishcooking/lebEmG5vgng%5B1-25%5D>
Based on recent improvement of futility pruning by @locutus2 : we lower
the futility margin to apply it for more nodes but as a compensation
we also lower the history threshold to apply it to less nodes. Further
work in tweaking constants can always be done - numbers are guessed
"by hand" and are not results of some tuning, maybe there is some more
Elo to squeeze from this part of code.
Passed STC
LLR: 2.98 (-2.94,2.94) {-1.00,3.00}
Total: 15300 W: 3081 L: 2936 D: 9283
Ptnml(0-2): 260, 1816, 3382, 1900, 290
http://tests.stockfishchess.org/tests/view/5e18da3b27dab692fcf9a158
Passed LTC
LLR: 2.94 (-2.94,2.94) {0.00,2.00}
Total: 108670 W: 14509 L: 14070 D: 80091
Ptnml(0-2): 813, 10259, 31736, 10665, 831
http://tests.stockfishchess.org/tests/view/5e18fc9627dab692fcf9a180
Bench: 4643972
