+-------+
| o . . | o their pawns
| x . . | x our pawns
| . x . | <- Can sacrifice to create passer?
+-------+
yes
1 2 3 4 5
+-------+ +-------+ +-------+ +-------+ +-------+
| o . . | | o r . | | o r . | | o . b | | o . b | lowercase: theirs
| x b . | | x . . | | x . R | | x . R | | x . . | uppercase: ours
| . x . | | . x . | | . x . | | . x . | | . x B |
+-------+ +-------+ +-------+ +-------+ +-------+
no no yes no yes
The value of our top pawn depends on our ability to advance our bottom
pawn, levering their blocker. Previously, this pawn configuration was
always scored as passer (although a blocked one).
Add requirements for the square s above our (possibly) sacrificed pawn:
- s must not be occupied by them (1).
- If they attack s (2), we must attack s (3).
- If they attack s with a minor (4), we must attack s with a minor (5).
The attack from their blocker is ignored because it is inherent in the
structure; we are ok with sacrificing our bottom pawn.
LTC
LLR: 2.95 (-2.94,2.94) {0.25,1.75}
Total: 37030 W: 4962 L: 4682 D: 27386
Ptnml(0-2): 266, 3445, 10863, 3625, 316
https://tests.stockfishchess.org/tests/view/5e92a2b4be6ede5b954bf239
STC
LLR: 2.94 (-2.94,2.94) {-0.50,1.50}
Total: 40874 W: 8066 L: 7813 D: 24995
Ptnml(0-2): 706, 4753, 9324, 4890, 764
https://tests.stockfishchess.org/tests/view/5e922199af0a0143109dc90e
closes https://github.com/official-stockfish/Stockfish/pull/2624
Bench: 4828294
In master, if the received ttMove meets the prescribed conditions in the various MovePicker constructors, it is returned as the first move, otherwise we set it to MOVE_NONE. If set to MOVE_NONE, we no longer track what the ttMove was, and it will might be returned later in a list of generated moves. This may be a waste. With this patch, if the ttMove fails to meet the prescribed conditions, we simply skip the TT stages, but still store the move and make sure it's never returned.
STC
LLR: 2.94 (-2.94,2.94) {-1.50,0.50}
Total: 66424 W: 12903 L: 12806 D: 40715
Ptnml(0-2): 1195, 7730, 15230, 7897, 1160
LTC
LLR: 2.94 (-2.94,2.94) {-1.50,0.50}
Total: 45682 W: 5989 L: 5926 D: 33767
Ptnml(0-2): 329, 4361, 13443, 4334, 374
closes https://github.com/official-stockfish/Stockfish/pull/2616
Bench 4928928
Before this commit, some pawns were considered "candidate" passed pawns and given half bonus. After this commit, all of these pawns are scored as passed pawns, and they do not receive less bonus.
STC:
LLR: 2.95 (-2.94,2.94) {-1.50,0.50}
Total: 21806 W: 4320 L: 4158 D: 13328
Ptnml(0-2): 367, 2526, 5001, 2596, 413
https://tests.stockfishchess.org/tests/view/5e86b4724411759d9d098639
LTC:
LLR: 2.95 (-2.94,2.94) {-1.50,0.50}
Total: 12590 W: 1734 L: 1617 D: 9239
Ptnml(0-2): 96, 1187, 3645, 1238, 129
https://tests.stockfishchess.org/tests/view/5e86d2874411759d9d098640
This PR and commit are dedicated to our colleague Stefan Geschwentner (@locutus2), one of the most respected and accomplished members of the Stockfish developer community. Stockfish is a volunteer project and has always thrived because of Stefan's talent, insight, generosity, and dedication. Welcome back, Stefan!
closes https://github.com/official-stockfish/Stockfish/pull/2613
Bench: 4831963
In more than 100k local KNPK games, there is no discernible difference between master and master with this endgame removed: master:42971, patch:42973, draws: 3969. Removal does not seem to regress in normal games.
STC
LLR: 2.94 (-2.94,2.94) {-1.50,0.50}
Total: 46390 W: 8998 L: 8884 D: 28508
Ptnml(0-2): 707, 5274, 11163, 5300, 751
https://tests.stockfishchess.org/tests/view/5e83b18ee42a5c3b3ca2ef02
LTC
LLR: 2.94 (-2.94,2.94) {-1.50,0.50}
Total: 44768 W: 5863 L: 5814 D: 33091
Ptnml(0-2): 251, 3918, 14028, 3905, 282
https://tests.stockfishchess.org/tests/view/5e84a82a4411759d9d0984f4
In tests with a book of endgames that can convert into KNPK, no significant difference can be seen either
```
TC 1.0+0.01
Score of patch vs master: 6131 - 6188 - 27681 [0.499] 40000
Elo difference: -0.5 +/- 1.9, LOS: 30.4 %, DrawRatio: 69.2 %
TC 2.0+0.02
Score of patch vs master: 5740 - 5741 - 28519 [0.500] 40000
Elo difference: -0.0 +/- 1.8, LOS: 49.6 %, DrawRatio: 71.3 %
``
closes https://github.com/official-stockfish/Stockfish/pull/2611
Bench 4512059
The idea behind this patch is that if static eval is really bad so capturing of current piece on spot will still produce a position with an eval much lower than alpha then our best chance is to create some kind of king attack. So captures without check are mostly worse than captures with check and can be reduced more.
passed STC
https://tests.stockfishchess.org/tests/view/5e8514b44411759d9d098543
LLR: 2.94 (-2.94,2.94) {-0.50,1.50}
Total: 46196 W: 9039 L: 8781 D: 28376
Ptnml(0-2): 750, 5412, 10628, 5446, 862
passed LTC
https://tests.stockfishchess.org/tests/view/5e8530134411759d9d09854c
LLR: 2.94 (-2.94,2.94) {0.25,1.75}
Total: 23462 W: 3228 L: 2988 D: 17246
Ptnml(0-2): 186, 2125, 6849, 2405, 166
close https://github.com/official-stockfish/Stockfish/pull/2612
bench 4742598
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
