Stockfish Development Versions are build automatically if there are changes on the master branch in the git repository (https://github.com/official-stockfish/Stockfish). Use it at your own risk.
They are compiled with gcc 11.2/mingw 10 on Ubuntu 22.04.

Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: xoto10
Date: Sat May 9 09:39:52 2020 +0200
Timestamp: 1589009992

Fix syzygy dependencies issue

fixes https://github.com/official-stockfish/Stockfish/issues/2660

The problem was caused by .depend being created with a rule for tbprobe.o not for syzygy/tbprobe.o.
This patch keeps an explicit list of sources (SRCS), generates OBJS,
and compiles all object files to the src/ directory, consistent with .depend.
VPATH is used to search the syzygy directory as needed.

joint work with @gvreuls

closes https://github.com/official-stockfish/Stockfish/pull/2664

No functional change
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: xoto10
Date: Wed May 6 16:20:01 2020 +0200
Timestamp: 1588774801

Penalty for all enemy pawns xrayed by our bishop.

STC:
LLR: 2.93 (-2.94,2.94) {-0.50,1.50}
Total: 159760 W: 30229 L: 29813 D: 99718 Elo +0.90
Ptnml(0-2): 2659, 18309, 37534, 18713, 2665
https://tests.stockfishchess.org/tests/view/5eb1d5032326444a3b6d33ce

LTC:
LLR: 2.93 (-2.94,2.94) {0.25,1.75}
Total: 26496 W: 3908 L: 3656 D: 18932 Elo +3.30
Ptnml(0-2): 192, 2512, 7610, 2720, 214
https://tests.stockfishchess.org/tests/view/5eb1e2dd2326444a3b6d33f9

closes https://github.com/official-stockfish/Stockfish/pull/2662

Bench 5185517
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: Marco Costalba
Date: Sat May 2 17:32:11 2020 +0200
Timestamp: 1588433531

Fishtest Tuning Framework

The purpose of the code is to allow developers to easily and flexibly
setup SF for a tuning session. Mainly you have just to remove 'const'
qualifiers from the variables you want to tune and flag them for
tuning, so if you have:

int myKing = 10;
Score myBonus = S(5, 15);
Value myValue[][2] = { { V(100), V(20) }, { V(7), V(78) } };

and at the end of the update you may want to call
a post update function:

void my_post_update();

If instead of default Option's min-max values,
you prefer your custom ones, returned by:

std::pair<int, int> my_range(int value)

Or you jus want to set the range directly, you can
simply add below:

TUNE(SetRange(my_range), myKing, SetRange(-200, 200), myBonus, myValue, my_post_update);

And all the magic happens :-)

At startup all the parameters are printed in a
format suitable to be copy-pasted in fishtest.

In case the post update function is slow and you have many
parameters to tune, you can add:

UPDATE_ON_LAST();

And the values update, including post update function call, will
be done only once, after the engine receives the last UCI option.
The last option is the one defined and created as the last one, so
this assumes that the GUI sends the options in the same order in
which have been defined.

closes https://github.com/official-stockfish/Stockfish/pull/2654

No functional change.
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: Vizvezdenec
Date: Sat May 2 17:30:22 2020 +0200
Timestamp: 1588433422

Refine scale factor of opposite colored bishops endgames.

This patch makes it dependant on the count of passed pawns of
the strong side instead of 22/64 in every case.

passed STC
https://tests.stockfishchess.org/tests/view/5ead60966ffeed51f6e32591
LLR: 2.96 (-2.94,2.94) {-0.50,1.50}
Total: 50336 W: 9473 L: 9241 D: 31622 Elo +1.60
Ptnml(0-2): 570, 5371, 13098, 5515, 614

passed LTC
https://tests.stockfishchess.org/tests/view/5ead6d3b6ffeed51f6e325b0
LLR: 2.94 (-2.94,2.94) {0.25,1.75}
Total: 21952 W: 2810 L: 2603 D: 16539 Elo +3.28
Ptnml(0-2): 101, 1791, 7005, 1958, 121

closes https://github.com/official-stockfish/Stockfish/pull/2658

bench 4247490
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: Linmiao Xu
Date: Sat May 2 17:26:51 2020 +0200
Timestamp: 1588433211

Tuned safe checks and minor piece king protectors

A combination of terms related to king safety one tuned safe check weights,
the other tuned knight and bishop king protector weights separately with
some compensation in the high outpost bonuses given to the minor pieces.

passed STC
LLR: 2.95 (-2.94,2.94) {-0.50,1.50}
Total: 39892 W: 7594 L: 7350 D: 24948 Elo +2.13
Ptnml(0-2): 643, 4559, 9314, 4771, 659
https://tests.stockfishchess.org/tests/view/5ea49635b908f6dd28f34b82

passed LTC
LLR: 2.94 (-2.94,2.94) {0.25,1.75}
Total: 104934 W: 13300 L: 12834 D: 78800 Elo +1.54
Ptnml(0-2): 697, 9571, 31514, 9939, 746
https://tests.stockfishchess.org/tests/view/5ea4abf6b908f6dd28f34bcb

closes https://github.com/official-stockfish/Stockfish/pull/2649

Bench 4800754
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: Joost VandeVondele
Date: Wed Apr 29 17:44:24 2020 +0200
Timestamp: 1588175064

Small cleanups

closes https://github.com/official-stockfish/Stockfish/pull/2628

No functional change
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: Vizvezdenec
Date: Wed Apr 29 17:35:48 2020 +0200
Timestamp: 1588174548

Introduce futility pruning for captures

The idea is somewhat similar to futility pruning for quiet moves -
if a late enough capture doesn't give check and the static eval is
much lower than alpha we can almost safely assume that this capture
wouldn't be a good move.

passed STC
https://tests.stockfishchess.org/tests/view/5ea8544b53a4548a0348ee5b
LLR: 2.95 (-2.94,2.94) {-0.50,1.50}
Total: 236040 W: 44420 L: 43894 D: 147726 Elo +0.77
Ptnml(0-2): 3830, 27202, 55496, 27596, 3896

passed LTC
https://tests.stockfishchess.org/tests/view/5ea87c842141237a731f0c7d
LLR: 2.95 (-2.94,2.94) {0.25,1.75}
Total: 81336 W: 10429 L: 10028 D: 60879 Elo +1.71
Ptnml(0-2): 589, 7356, 24404, 7703, 616

closes https://github.com/official-stockfish/Stockfish/pull/2651

bench 4405247
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: pb00067
Date: Wed Apr 22 08:48:01 2020 +0200
Timestamp: 1587538081

continuation histories when in check

If in check, don't write to continuation histories ss-4, ss-6.
Adding inCheck to the stack was needed, and might be useful for
future patches.

Passed STC:
https://tests.stockfishchess.org/tests/view/5e9ee24acaaff5d60a50b812
LLR: 2.94 (-2.94,2.94) {-0.50,1.50}
Total: 61774 W: 11725 L: 11449 D: 38600 Elo +1.55
Ptnml(0-2): 971, 7211, 14322, 7337, 1046

Passed LTC:
https://tests.stockfishchess.org/tests/view/5e9eecb7caaff5d60a50b831
LLR: 2.94 (-2.94,2.94) {0.25,1.75}
Total: 250822 W: 32067 L: 31179 D: 187576 Elo +1.23
Ptnml(0-2): 1745, 23126, 74824, 23928, 1788

closes https://github.com/official-stockfish/Stockfish/pull/2645

bench: 4808463
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: Vizvezdenec
Date: Sat Apr 18 15:36:41 2020 +0200
Timestamp: 1587217001

Apply multicut pruning more often

This patch increases number of nodes where we produce multicut cutoffs.

The idea is that if our ttMove failed to produce a singular extension
but ttValue is greater than beta we can afford to do one more reduced search
near beta excluding ttMove to see if it will produce a fail high -
and if it does so produce muticut by analogy to existing logic.

passed STC
https://tests.stockfishchess.org/tests/view/5e9a162b5b664cdba0ce6e28
LLR: 2.94 (-2.94,2.94) {-0.50,1.50}
Total: 58238 W: 11192 L: 10917 D: 36129 Elo +1.64
Ptnml(0-2): 1007, 6704, 13442, 6939, 1027

passed LTC
https://tests.stockfishchess.org/tests/view/5e9a1e845b664cdba0ce7411
LLR: 2.94 (-2.94,2.94) {0.25,1.75}
Total: 137852 W: 17460 L: 16899 D: 103493 Elo +1.41
Ptnml(0-2): 916, 12610, 41383, 13031, 986

closes https://github.com/official-stockfish/Stockfish/pull/2640

bench 4881443
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: protonspring
Date: Sat Apr 18 15:29:24 2020 +0200
Timestamp: 1587216564

Simplify minPawnDistance

This is a functional simplification which fixes an awkward numerical cliff.

With master king_safety, no pawns is scored higher than pawn(s) that is/are far from the king. This may motivate SF to throw away pawns to increase king safety. With this patch, there is a consistent value for minPawnDistance where losing a pawn never increases king safety.

STC
LLR: 2.94 (-2.94,2.94) {-1.50,0.50}
Total: 45548 W: 8624 L: 8525 D: 28399 Elo +0.76
Ptnml(0-2): 592, 4937, 11587, 5096, 562
https://tests.stockfishchess.org/tests/view/5e98ced630be947a14e9ddc5

LTC
LLR: 2.94 (-2.94,2.94) {-1.50,0.50}
Total: 42084 W: 5292 L: 5242 D: 31550 Elo +0.41
Ptnml(0-2): 193, 3703, 13252, 3649, 245
https://tests.stockfishchess.org/tests/view/5e98e22e30be947a14e9de07

closes https://github.com/official-stockfish/Stockfish/pull/2639

bench 4600292
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: Joost VandeVondele
Date: Thu Apr 16 21:44:52 2020 +0200
Timestamp: 1587066292

Remove one condition in probcut TTmove skipping

the removed condition appears illogical and is not needed.

passed STC:
LLR: 2.95 (-2.94,2.94) {-1.50,0.50}
Total: 80418 W: 15217 L: 15144 D: 50057 Elo +0.32
Ptnml(0-2): 1341, 9399, 18679, 9426, 1364
https://tests.stockfishchess.org/tests/view/5e977eb5c9ada107a0370d6b

passed LTC:
LLR: 2.95 (-2.94,2.94) {-1.50,0.50}
Total: 49878 W: 6299 L: 6247 D: 37332 Elo +0.36
Ptnml(0-2): 327, 4677, 14897, 4693, 345
https://tests.stockfishchess.org/tests/view/5e97e07dc9ada107a0370e53

closes https://github.com/official-stockfish/Stockfish/pull/2638

Bench: 4958027
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: xoto10
Date: Thu Apr 16 21:40:06 2020 +0200
Timestamp: 1587066006

Scale factor in opposite-color bishop endings

This change varies the scale factor with the total number of pieces and pawns on the strongSide.

STC :
LLR: 2.94 (-2.94,2.94) {-0.50,1.50}
Total: 150920 W: 28828 L: 28422 D: 93670 Elo +0.93
Ptnml(0-2): 2507, 17548, 35030, 17782, 2593
https://tests.stockfishchess.org/tests/view/5e983eb2c00499c5410f4951

LTC :
LLR: 2.95 (-2.94,2.94) {0.25,1.75}
Total: 69238 W: 8810 L: 8446 D: 51982 Elo +1.83
Ptnml(0-2): 451, 6276, 20879, 6484, 529
https://tests.stockfishchess.org/tests/view/5e985b27c00499c5410f4987

closes https://github.com/official-stockfish/Stockfish/pull/2637

Bench 4821332
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: Lolligerhans
Date: Thu Apr 16 21:36:19 2020 +0200
Timestamp: 1587065779

Increase safe check bonus if multiple safe checks

Add 50% "safe checks" bonus when there are multiple safe checks from the
same piece type.

LTC
LLR: 2.97 (-2.94,2.94) {0.25,1.75}
Total: 128184 W: 16491 L: 15954 D: 95739 Elo +1.46
Ptnml(0-2): 884, 11793, 38267, 12198, 950
https://tests.stockfishchess.org/tests/view/5e97d1b6c9ada107a0370e03

STC
LLR: 2.94 (-2.94,2.94) {-0.50,1.50}
Total: 19022 W: 3733 L: 3514 D: 11775 Elo +4.00
Ptnml(0-2): 338, 2103, 4414, 2314, 342
https://tests.stockfishchess.org/tests/view/5e97c377c9ada107a0370ddf

closes https://github.com/official-stockfish/Stockfish/pull/2636

Bench: 5057329
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: FauziAkram
Date: Thu Apr 16 21:32:26 2020 +0200
Timestamp: 1587065546

Queen and Rook Tuning

Tuning for multiple parameters for Queen and Rook.

passed STC
LLR: 2.94 (-2.94,2.94) {-0.50,1.50}
Total: 62790 W: 12033 L: 11754 D: 39003 Elo +1.54
Ptnml(0-2): 1058, 7186, 14666, 7389, 1096
https://tests.stockfishchess.org/tests/view/5e978c66c9ada107a0370d87

passed LTC
LLR: 2.95 (-2.94,2.94) {0.25,1.75}
Total: 89780 W: 11460 L: 11036 D: 67284 Elo +1.64
Ptnml(0-2): 624, 8151, 26951, 8505, 659
https://tests.stockfishchess.org/tests/view/5e979aaec9ada107a0370d93

closes https://github.com/official-stockfish/Stockfish/pull/2634

Bench: 5111578
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: Vizvezdenec
Date: Wed Apr 15 20:33:03 2020 +0200
Timestamp: 1586975583

Don't attempt probcut if ttMove is not good enough.

This idea is loosely based on xoroshiro idea about raisedBeta and ttmoves.
If our ttmove have low enough ttvalue and is deep enough (deeper than our probcut depth) it makes little sense to try probcut moves, since the ttMove already more or less failed to produce one according to transposition table.

passed STC
https://tests.stockfishchess.org/tests/view/5e9673ddc2718dee3c822920
LLR: 2.95 (-2.94,2.94) {-0.50,1.50}
Total: 72148 W: 14038 L: 13741 D: 44369 Elo +1.43
Ptnml(0-2): 1274, 8326, 16615, 8547, 1312

passed LTC
https://tests.stockfishchess.org/tests/view/5e96b378c2718dee3c8229bf
LLR: 2.94 (-2.94,2.94) {0.25,1.75}
Total: 89054 W: 11418 L: 10996 D: 66640 Elo +1.65
Ptnml(0-2): 623, 8113, 26643, 8515, 633

closes https://github.com/official-stockfish/Stockfish/pull/2632

bench 4952731
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: Vizvezdenec
Date: Wed Apr 15 08:29:20 2020 +0200
Timestamp: 1586932160

Space bonus and number of blocked pawns

This patch refines the recently introduced interaction between
the space bonus and the number of blocked pawns in a position.

* pawns count as blocked also if their push square is attacked by 2 enemy pawns;
* overall dependence is stronger as well as offset;
* bonus increase is capped at 9 blocked pawns in position;

passed STC
https://tests.stockfishchess.org/tests/view/5e94560663d105aebbab243d
LLR: 2.96 (-2.94,2.94) {-0.50,1.50}
Total: 29500 W: 5842 L: 5603 D: 18055 Elo +2.81
Ptnml(0-2): 504, 3443, 6677, 3562, 564

passed LTC
https://tests.stockfishchess.org/tests/view/5e95b383c2aaa99f75d1a14d
LLR: 2.95 (-2.94,2.94) {0.25,1.75}
Total: 63504 W: 8329 L: 7974 D: 47201 Elo +1.94
Ptnml(0-2): 492, 5848, 18720, 6197, 495

closes https://github.com/official-stockfish/Stockfish/pull/2631

bench 4956028
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: Stefan Geschwentner
Date: Tue Apr 14 08:01:53 2020 +0200
Timestamp: 1586844113

less bonus for blocked connected pawn

Use less bonus for blocked connected pawns so closed positions are less worth.

STC:
LLR: 2.96 (-2.94,2.94) {-0.50,1.50}
Total: 60004 W: 11904 L: 11619 D: 36481 Elo +1.65
Ptnml(0-2): 1066, 7083, 13535, 7136, 1182
https://tests.stockfishchess.org/tests/view/5e941a8063d105aebbab23e3

LTC:
LLR: 2.95 (-2.94,2.94) {0.25,1.75}
Total: 36606 W: 4831 L: 4556 D: 27219 Elo +2.61
Ptnml(0-2): 252, 3353, 10872, 3520, 306
https://tests.stockfishchess.org/tests/view/5e9444b963d105aebbab2427

closes https://github.com/official-stockfish/Stockfish/pull/2629

Bench: 4961260
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: silversolver1
Date: Mon Apr 13 09:20:53 2020 +0200
Timestamp: 1586762453

Removes evasionPrunable

STC:
LLR: 2.95 (-2.94,2.94) {-1.50,0.50}
Total: 25656 W: 4979 L: 4826 D: 15851 Elo +2.07
Ptnml(0-2): 414, 2971, 5964, 3006, 473
https://tests.stockfishchess.org/tests/view/5e93dbd72cb65b3059c33819

LTC:
LLR: 2.94 (-2.94,2.94) {-1.50,0.50}
Total: 43732 W: 5656 L: 5593 D: 32483 Elo +0.50
Ptnml(0-2): 324, 4072, 13009, 4139, 322
https://tests.stockfishchess.org/tests/view/5e93e37c2cb65b3059c33825

closes https://github.com/official-stockfish/Stockfish/pull/2627

Bench: 4702195
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: Vizvezdenec
Date: Mon Apr 13 09:16:54 2020 +0200
Timestamp: 1586762214

Scale up space weight with number of blocked pawns

This idea is loosely based on stockfish losses in closed positions in different tournaments. Space weight symmetrically increases for both sides the more blocked position is.

passed STC
https://tests.stockfishchess.org/tests/view/5e919eefaf0a0143109dc8ce
LLR: 2.94 (-2.94,2.94) {-0.50,1.50}
Total: 16994 W: 3389 L: 3172 D: 10433 Elo +4.44
Ptnml(0-2): 277, 1931, 3918, 2040, 331

passed LTC
https://tests.stockfishchess.org/tests/view/5e91d04faf0a0143109dc8ea
LLR: 2.94 (-2.94,2.94) {0.25,1.75}
Total: 133386 W: 17316 L: 16763 D: 99307 Elo +1.44
Ptnml(0-2): 945, 12407, 39524, 12784, 1033

closes https://github.com/official-stockfish/Stockfish/pull/2626

Bench: 4966867
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: Lolligerhans
Date: Mon Apr 13 08:50:25 2020 +0200
Timestamp: 1586760625

Remove candidate passers w/o feasible lever

+-------+
| 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 Elo +2.63
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 Elo +2.15
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
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: Joost VandeVondele
Date: Sun Apr 12 20:38:47 2020 +0200
Timestamp: 1586716727

Extend irreversible moves

if these are ttMoves and played in positions with a high value of the rule50 counter. The unusual extension of 2 is safe in this context as awarding it will reset the rule50 counter, making sure it is awarded very rarely in a search path.

This patch partially addresses https://github.com/official-stockfish/Stockfish/issues/2620 as it should make it less likely to play a move that resets the counter, but that is worse than alternative moves after a slightly deeper search.

passed STC:
LLR: 2.96 (-2.94,2.94) {-0.50,1.50}
Total: 71658 W: 13840 L: 13560 D: 44258 Elo +1.36
Ptnml(0-2): 1058, 7921, 17643, 8097, 1110
https://tests.stockfishchess.org/tests/view/5e90d0f6754c3424c4cf9f41

passed LTC:
LLR: 2.94 (-2.94,2.94) {0.25,1.75}
Total: 85082 W: 11069 L: 10680 D: 63333 Elo +1.59
Ptnml(0-2): 459, 6982, 27259, 7393, 448
https://tests.stockfishchess.org/tests/view/5e917470af0a0143109dc341

closes https://github.com/official-stockfish/Stockfish/pull/2623

Bench: 4432822
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: protonspring
Date: Sun Apr 12 20:34:50 2020 +0200
Timestamp: 1586716490

Always remember the ttMove

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 Elo +0.51
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 Elo +0.48
Ptnml(0-2): 329, 4361, 13443, 4334, 374

closes https://github.com/official-stockfish/Stockfish/pull/2616

Bench 4928928
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: Joost VandeVondele
Date: Sun Apr 12 20:30:08 2020 +0200
Timestamp: 1586716208

Small cleanups

closes https://github.com/official-stockfish/Stockfish/pull/2606

No functional change
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: Vizvezdenec
Date: Tue Apr 7 17:47:01 2020 +0200
Timestamp: 1586274421

Introduce capture history pruning

This patch introduces a heuristic that is similar to countermove based pruning but for captures - capture history pruning. The idea is that we can (almost) safely prune really late captures with negative history if they don't give check so will most likely not produce some king-attacking tactic.

passed STC
https://tests.stockfishchess.org/tests/view/5e8c60d40ffd2be7f15e5470
LLR: 2.94 (-2.94,2.94) {-0.50,1.50}
Total: 23748 W: 4758 L: 4529 D: 14461 Elo +3.35
Ptnml(0-2): 421, 2712, 5400, 2899, 442

passed LTC
https://tests.stockfishchess.org/tests/view/5e8c72bf0ffd2be7f15e547f
LLR: 2.96 (-2.94,2.94) {0.25,1.75}
Total: 17330 W: 2415 L: 2190 D: 12725 Elo +4.51
Ptnml(0-2): 126, 1561, 5107, 1704, 167

closes https://github.com/official-stockfish/Stockfish/pull/2618

bench 4417023
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: Vizvezdenec
Date: Sun Apr 5 08:44:25 2020 +0200
Timestamp: 1586069065

Further increase reductions with increasing number of threads

This patch doubles the reduction increase with thread count.

passed STC
https://tests.stockfishchess.org/tests/view/5e874f5a4411759d9d098696
LLR: 2.94 (-2.94,2.94) {-0.50,1.50}
Total: 9162 W: 1558 L: 1385 D: 6219 Elo +6.56
Ptnml(0-2): 90, 958, 2343, 1069, 121

passed LTC
https://tests.stockfishchess.org/tests/view/5e8762804411759d9d09869f
LLR: 2.94 (-2.94,2.94) {0.25,1.75}
Total: 79364 W: 9541 L: 9159 D: 60664 Elo +1.67
Ptnml(0-2): 462, 6880, 24661, 7172, 507

closes https://github.com/official-stockfish/Stockfish/pull/2615

bench 4831963
see source

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