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 + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Stéphane Nicolet
Date: Thu Apr 15 11:19:44 2021 +0200
Timestamp: 1618478384

Revert previous patch

Revert the previous patch about move generation, as it unexpectedly
changed the bench. Better to take the time to understand the issue.

Bench: 4191632
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: bmc4
Date: Thu Apr 15 10:53:51 2021 +0200
Timestamp: 1618476831

Merge all move generators

Merging `generate<EVASIONS>` and `generate<QUIET_CHECKS>` into `generate_all()`.

STC:
LLR: 2.94 (-2.94,2.94) {-1.00,0.20}
Total: 161800 W: 14585 L: 14624 D: 132591 Elo -0.08
Ptnml(0-2): 577, 11681, 56451, 11586, 605
https://tests.stockfishchess.org/tests/view/606532732b2df919fd5f026d

LTC:
LLR: 2.98 (-2.94,2.94) {-0.70,0.20}
Total: 188504 W: 6906 L: 6961 D: 174637 Elo -0.10
Ptnml(0-2): 87, 6272, 81610, 6175, 108
https://tests.stockfishchess.org/tests/view/6065b0772b2df919fd5f02ae

------------

Verified for correctness of `EVASIONS` by running perft:
```
./stockfish b3nch 16 1 6 default perft (replace 3 by e in b3nch)
Nodes searched : 71608931810
```

Also tested for correctness on Chess960 with a similar code shown here:
https://github.com/official-stockfish/Stockfish/pull/3418#issuecomment-816630295

```
./stockfish b3nch 16 1 6 fischer.txt perft
Nodes searched : 506736009395
```

------------

Closes https://github.com/official-stockfish/Stockfish/pull/3418

No functional change
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Vizvezdenec
Date: Tue Apr 6 18:23:35 2021 +0200
Timestamp: 1617726215

Replace distanceFromPv with a better logic

This patch removes the recently introduced distanceFromPv logic, and replaces
it with following logic: if reduction of moves with low movecount is really
negative, we search them deeper than the first move.

passed STC:
LLR: 2.95 (-2.94,2.94) {-0.20,1.10}
Total: 153008 W: 13913 L: 13579 D: 125516 Elo +0.76
Ptnml(0-2): 547, 10811, 53470, 11113, 563
https://tests.stockfishchess.org/tests/view/6069c9d02b2df919fd5f04d2

passed LTC:
LLR: 2.94 (-2.94,2.94) {0.20,0.90}
Total: 101920 W: 3964 L: 3699 D: 94257 Elo +0.90
Ptnml(0-2): 55, 3279, 44019, 3560, 47
https://tests.stockfishchess.org/tests/view/606a99fd2b2df919fd5f0532

Closes https://github.com/official-stockfish/Stockfish/pull/3421

Bench: 4191632
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Stéphane Nicolet
Date: Tue Apr 6 09:07:20 2021 +0200
Timestamp: 1617692840

Keep more pawns

This patch increases the weight of pawns in the scale factor applied
to the output of the NNUE evaluation. This has the effect that Stockfish
will try a little bit harder to keep more pawns in position where the
engine has the advantage, and exchange more pawns in bad positions.

STC:
LLR: 2.93 (-2.94,2.94) {-0.20,1.10}
Total: 42552 W: 3858 L: 3668 D: 35026 Elo +1.55
Ptnml(0-2): 152, 2956, 14876, 3134, 158
https://tests.stockfishchess.org/tests/view/606a06dd2b2df919fd5f0504

LTC:
LLR: 2.95 (-2.94,2.94) {0.20,0.90}
Total: 44328 W: 1703 L: 1531 D: 41094 Elo +1.35
Ptnml(0-2): 20, 1373, 19207, 1543, 21
https://tests.stockfishchess.org/tests/view/606aa4ec2b2df919fd5f053e

Closes https://github.com/official-stockfish/Stockfish/pull/3420

Bench: 4310076
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Stéphane Nicolet
Date: Wed Mar 31 08:12:25 2021 +0200
Timestamp: 1617171145

Small clean-up

Bench: 4321677
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: bmc4
Date: Wed Mar 31 07:47:15 2021 +0200
Timestamp: 1617169635

Simplify King Evasion

Simplify away the removal of some illegal `KING`-evasion moves during move
generation. Verified for correctness by running perft on the following positions:

```
./stockfish
bench 16 1 6 default perft
Nodes searched: 71608931810

./stockfish
position fen 4rrk1/1p1nq3/p7/2p1P1pp/3P2bp/3Q1Bn1/PPPB4/1K2R1NR w - - 40 21
go perft 6
Nodes searched: 6136386434
```

Passed STC:
LLR: 2.94 (-2.94,2.94) {-1.00,0.20}
Total: 16072 W: 1473 L: 1349 D: 13250 Elo +2.68
Ptnml(0-2): 57, 1047, 5710, 1159, 63
https://tests.stockfishchess.org/tests/view/60629e7ef183b42957b423b1

Passed LTC:
LLR: 2.94 (-2.94,2.94) {-0.70,0.20}
Total: 59064 W: 2214 L: 2177 D: 54673 Elo +0.22
Ptnml(0-2): 26, 1944, 25556, 1979, 27
https://tests.stockfishchess.org/tests/view/6062dce4f183b42957b423de

closes https://github.com/official-stockfish/Stockfish/pull/3415

No functional change
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: mstembera
Date: Sat Mar 27 17:03:10 2021 +0100
Timestamp: 1616860990

Simplify and unify FRC cornered bishop.

tested locally as fishtest doesn't support FRC:

STC NNUE
9646 - 9647 - 20707 [0.500] 40000 -0.0 +/- 2.4, LOS: 49.7 %, DrawRatio: 51.8 %

STC classical
9678 - 9609 - 20713 [0.501] 40000 0.6 +/- 2.4, LOS: 69.0 %, DrawRatio: 51.8 %

and verified independently:

Score of master vs patch: 6463 - 6580 - 34957 [0.499] 48000

closes https://github.com/official-stockfish/Stockfish/pull/3413

bench: 4321677
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Tomasz Sobczyk
Date: Sat Mar 27 16:56:05 2021 +0100
Timestamp: 1616860565

Allow using Intel SDE for PGO builds.

The software development emulator (SDE) allows to run binaries compiled
for architectures not supported by the actual CPU. This is useful to
do PGO builds for newer architectures. The SDE can currently be obtained from
https://software.intel.com/content/www/us/en/develop/articles/intel-software-development-emulator.html

This patch introduces a new optional makefile argument SDE_PATH.
If not empty it should contain the path to the sde executable

closes https://github.com/official-stockfish/Stockfish/pull/3373

No functional change.
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Stéphane Nicolet
Date: Wed Mar 24 17:11:06 2021 +0100
Timestamp: 1616602266

Small cleanups (march 2021)

With help of @BM123499, @mstembera, @gvreuls, @noobpwnftw and @Fanael
Thanks!

Closes https://github.com/official-stockfish/Stockfish/pull/3405

No functional change
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Guy Vreuls
Date: Fri Mar 19 20:28:57 2021 +0100
Timestamp: 1616182137

Use reference instead of pointer for pop_lsb() signature

This patch changes the pop_lsb() signature from Square pop_lsb(Bitboard*) to
Square pop_lsb(Bitboard&). This is more idomatic for C++ style signatures.

Passed a non-regression STC test:
LLR: 2.93 (-2.94,2.94) {-1.25,0.25}
Total: 21280 W: 1928 L: 1847 D: 17505 Elo +1.32
Ptnml(0-2): 71, 1427, 7558, 1518, 66
https://tests.stockfishchess.org/tests/view/6053a1e22433018de7a38e2f

We have verified that the generated binary is identical on gcc-10.

Closes https://github.com/official-stockfish/Stockfish/pull/3404

No functional change.
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Vizvezdenec
Date: Fri Mar 19 11:58:17 2021 +0100
Timestamp: 1616151497

Add a specific FRC correction from classical to NNUE

our net currently is not trained on FRC games, and so doesn't know about the important pattern of a bishop that is cornered in FRC.
This patch introduces a term we have in the classical evaluation for this case, and adds it to the NNUE eval.

Since fishtest doesn't support FRC right now, the patch was tested locally at STC conditions,
starting from the book of FRC starting positions.

Score of master vs patch: 993 - 2226 - 6781 [0.438] 10000

Which corresponds to approximately 40 Elo

The patch passes non-regression testing for traditional chess (where it adds one branch).

passed STC:
https://tests.stockfishchess.org/tests/view/604fa2532433018de7a38b67
LLR: 2.95 (-2.94,2.94) {-1.25,0.25}
Total: 30560 W: 2701 L: 2636 D: 25223 Elo +0.74
Ptnml(0-2): 88, 2056, 10921, 2133, 82

passed STC also in an earlier version:
https://tests.stockfishchess.org/tests/view/604f61282433018de7a38b4d

closes https://github.com/official-stockfish/Stockfish/pull/3398

No functional change
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: bmc4
Date: Thu Mar 18 00:21:41 2021 +0100
Timestamp: 1616023301

Change definition of between_bb()

We remark that in current master, most of our use cases for between_bb() can be
optimized if the second parameter of the function is added to the segment. So we
change the definition of between_bb(s1, s2) such that it excludes s1 but includes s2.

We also use a precomputed array for between_bb() for another small speed gain
(see https://tests.stockfishchess.org/tests/view/604d09f72433018de7a389fb).

Passed STC:
LLR: 2.96 (-2.94,2.94) {-0.25,1.25}
Total: 18736 W: 1746 L: 1607 D: 15383 Elo +2.58
Ptnml(0-2): 61, 1226, 6644, 1387, 50
https://tests.stockfishchess.org/tests/view/60428c84ddcba5f0627bb6e4

Yellow LTC:
LTC:
LLR: -3.00 (-2.94,2.94) {0.25,1.25}
Total: 39144 W: 1431 L: 1413 D: 36300 Elo +0.16
Ptnml(0-2): 13, 1176, 17184, 1178, 21
https://tests.stockfishchess.org/tests/view/605128702433018de7a38ca1

Closes https://github.com/official-stockfish/Stockfish/pull/3397

---------

Verified for correctness by running perft on the following position:

./stockfish
position fen 4rrk1/1p1nq3/p7/2p1P1pp/3P2bp/3Q1Bn1/PPPB4/1K2R1NR w - - 40 21
go perft 6

Nodes searched: 6136386434

--------

No functional change
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Vizvezdenec
Date: Wed Mar 17 10:34:02 2021 +0100
Timestamp: 1615973642

Remove advanced_pawn_push()

Continuation of work by @topologist: we now do futility pruning and movecount
pruning in qsearch() for pawn pushes up to the 7th rank. So the condition to
avoid the pruning is if the move is a promotion or not. This allows to get rid
of the advanced_pawn_push() function in position.h alltogether.

Passed STC
https://tests.stockfishchess.org/tests/view/6048c5842433018de7a387e6
LLR: 2.93 (-2.94,2.94) {-1.25,0.25}
Total: 34424 W: 3081 L: 3015 D: 28328 Elo +0.67
Ptnml(0-2): 110, 2442, 12052, 2488, 120

Passed LTC
https://tests.stockfishchess.org/tests/view/6048f7d22433018de7a387f0
LLR: 2.94 (-2.94,2.94) {-0.75,0.25}
Total: 142024 W: 5170 L: 5202 D: 131652 Elo -0.08
Ptnml(0-2): 50, 4678, 61613, 4596, 75

Closes https://github.com/official-stockfish/Stockfish/pull/3390

Bench: 4339126
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: bmc4
Date: Tue Mar 16 22:34:23 2021 +0100
Timestamp: 1615930463

Simplify move generation (2/2)

STC:
LLR: 2.97 (-2.94,2.94) {-1.25,0.25}
Total: 39352 W: 3551 L: 3493 D: 32308 Elo +0.51
Ptnml(0-2): 143, 2695, 13928, 2781, 129
https://tests.stockfishchess.org/tests/view/6050007a2433018de7a38bbb

LTC:
LLR: 2.96 (-2.94,2.94) {-0.75,0.25}
Total: 44944 W: 1629 L: 1596 D: 41719 Elo +0.26
Ptnml(0-2): 22, 1319, 19762, 1342, 27
https://tests.stockfishchess.org/tests/view/60500e892433018de7a38bc4

Closes https://github.com/official-stockfish/Stockfish/pull/3399

No functional change
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: bmc4
Date: Tue Mar 16 22:32:53 2021 +0100
Timestamp: 1615930373

Simplify move generation (1/2)

STC:
LLR: 2.95 (-2.94,2.94) {-1.25,0.25}
Total: 29792 W: 2611 L: 2545 D: 24636 Elo +0.77
Ptnml(0-2): 94, 1982, 10659, 2086, 75
https://tests.stockfishchess.org/tests/view/604fe5b62433018de7a38ba8

LTC:
LLR: 2.92 (-2.94,2.94) {-0.75,0.25}
Total: 22040 W: 826 L: 777 D: 20437 Elo +0.77
Ptnml(0-2): 8, 646, 9664, 693, 9
https://tests.stockfishchess.org/tests/view/604fec892433018de7a38bac

Closes https://github.com/official-stockfish/Stockfish/pull/3399

No functional change
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: bmc4
Date: Tue Mar 16 20:54:52 2021 +0100
Timestamp: 1615924492

Introduce least_significant_square_bb()

Introducing least_significant_square_bb(). It is a function that returns a value equal
to square_bb(lsb(bb)), but it uses fewer instruction. It should speed up more on older
processors like armv7-a Clang.

Passed STC:
LLR: 2.93 (-2.94,2.94) {-0.25,1.25}
Total: 213200 W: 19171 L: 18753 D: 175276 Elo +0.68
Ptnml(0-2): 680, 14513, 75831, 14861, 715
https://tests.stockfishchess.org/tests/view/604bc7632433018de7a38982

Closes https://github.com/official-stockfish/Stockfish/pull/3391

No functional change
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Topologist
Date: Wed Mar 10 12:32:53 2021 +0100
Timestamp: 1615375973

Change advanced pawn push threshold

A pawn push is now considered to be "advanced" if the relative destination
rank is > 6 (previously it was > 5). This affects the search heuristic.

Also remove an assert concerning en passant moves in qsearch().

STC:
LLR: 2.97 (-2.94,2.94) {-0.25,1.25}
Total: 46744 W: 4224 L: 4040 D: 38480 Elo +1.37
Ptnml(0-2): 165, 3206, 16451, 3380, 170
https://tests.stockfishchess.org/tests/view/604746082433018de7a3872e

LTC:
LLR: 2.94 (-2.94,2.94) {0.25,1.25}
Total: 107840 W: 4198 L: 3892 D: 99750 Elo +0.99
Ptnml(0-2): 58, 3472, 46557, 3772, 61
https://tests.stockfishchess.org/tests/view/60475eae2433018de7a38737

Closes https://github.com/official-stockfish/Stockfish/pull/3389

Bench: 4796780
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: bmc4
Date: Sun Mar 7 21:16:38 2021 +0100
Timestamp: 1615148198

Use Bitboard over Square in movegen

It uses pos.checkers() on target when movegen is the type of EVASION.
It simplify the code. And it's also expected a slightly speed up,
because Bitboard is more direct when doing bitwise.

Passed STC:
LLR: 2.93 (-2.94,2.94) {-1.25,0.25}
Total: 28176 W: 2506 L: 2437 D: 23233 Elo +0.85
Ptnml(0-2): 80, 1904, 10063, 1949, 92
https://tests.stockfishchess.org/tests/view/60421d18ddcba5f0627bb6a9

Passed LTC:
LLR: 2.93 (-2.94,2.94) {-0.75,0.25}
Total: 9704 W: 402 L: 341 D: 8961 Elo +2.18
Ptnml(0-2): 3, 279, 4230, 334, 6
https://tests.stockfishchess.org/tests/view/60422823ddcba5f0627bb6ae

closes https://github.com/official-stockfish/Stockfish/pull/3383

No functional change
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: mattginsberg
Date: Sun Mar 7 21:10:04 2021 +0100
Timestamp: 1615147804

Deal with commented lines in UCI input

commands starting with '#' as the first character will be ignored

closes https://github.com/official-stockfish/Stockfish/pull/3378

No functional change
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: noobpwnftw
Date: Sun Mar 7 20:02:11 2021 +0100
Timestamp: 1615143731

Do not try to use large pages on 32 bit Windows.

verified to work on windows XP.

fixes #3379

closes https://github.com/official-stockfish/Stockfish/pull/3380

No functional change.
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Dieter Dobbelaere
Date: Sun Mar 7 14:26:54 2021 +0100
Timestamp: 1615123614

Add Stockfish namespace.

fixes #3350 and is a small cleanup that might make it easier to use SF
in separate projects, like a NNUE trainer or similar.

closes https://github.com/official-stockfish/Stockfish/pull/3370

No functional change.
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Antoine Champion
Date: Sun Mar 7 14:05:01 2021 +0100
Timestamp: 1615122301

Clean functions returning by const values

The codebase contains multiple functions returning by const-value.
This patch is a small cleanup making those function returns
by value instead, removing the const specifier.

closes https://github.com/official-stockfish/Stockfish/pull/3328

No functional change
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Stéphane Nicolet
Date: Fri Feb 26 19:45:29 2021 +0100
Timestamp: 1614365129

Introduce DistanceFromPV

We introduce a metric for each internal node in search, called DistanceFromPV.
This distance indicated how far the current node is from the principal variation.

We then use this distance to search the nodes which are close to the PV a little
deeper (up to 4 plies deeper than the PV): this improves the quality of the search
at these nodes and bring better updates for the PV during search.

STC:
LLR: 2.96 (-2.94,2.94) {-0.25,1.25}
Total: 54936 W: 5047 L: 4850 D: 45039 Elo +1.25
Ptnml(0-2): 183, 3907, 19075, 4136, 167
https://tests.stockfishchess.org/tests/view/6037b88e7f517a561bc4a392

LTC:
LLR: 2.95 (-2.94,2.94) {0.25,1.25}
Total: 49608 W: 1880 L: 1703 D: 46025 Elo +1.24
Ptnml(0-2): 22, 1514, 21555, 1691, 22
https://tests.stockfishchess.org/tests/view/6038271b7f517a561bc4a3cb

Closes https://github.com/official-stockfish/Stockfish/pull/3369

Bench: 5037279
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Vizvezdenec
Date: Sat Feb 20 22:49:39 2021 +0100
Timestamp: 1613857779

Introduce ProbCut for check evasions

The idea of this patch can be described as follows: if we are in check
and the transposition table move is a capture that returns a value
far above beta, we can assume that the opponent just blundered a piece
by giving check, and we return the transposition table value. This is
similar to the usual probCut logic for quiet moves, but with a different
threshold.

Passed STC
LLR: 2.94 (-2.94,2.94) {-0.25,1.25}
Total: 33440 W: 3056 L: 2891 D: 27493 Elo +1.71
Ptnml(0-2): 110, 2338, 11672, 2477, 123
https://tests.stockfishchess.org/tests/view/602cd1087f517a561bc49bda

Passed LTC
LLR: 2.98 (-2.94,2.94) {0.25,1.25}
Total: 10072 W: 401 L: 309 D: 9362 Elo +3.17
Ptnml(0-2): 2, 288, 4365, 378, 3
https://tests.stockfishchess.org/tests/view/602ceea57f517a561bc49bf0

The committed version has an additional fix to never return unproven wins
in the tablebase range or the mate range. This fix passed tests for non-
regression at STC and LTC:

STC:
LLR: 2.93 (-2.94,2.94) {-1.25,0.25}
Total: 26240 W: 2354 L: 2280 D: 21606 Elo +0.98
Ptnml(0-2): 85, 1763, 9372, 1793, 107
https://tests.stockfishchess.org/tests/view/602d86a87f517a561bc49c7a

LTC:
LLR: 2.95 (-2.94,2.94) {-0.75,0.25}
Total: 35304 W: 1299 L: 1256 D: 32749 Elo +0.42
Ptnml(0-2): 14, 1095, 15395, 1130, 18
https://tests.stockfishchess.org/tests/view/602d98d17f517a561bc49c83

Closes https://github.com/official-stockfish/Stockfish/pull/3362

Bench: 3830215
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Vizvezdenec
Date: Sat Feb 20 22:22:07 2021 +0100
Timestamp: 1613856127

Tune search parameters (with Unai Corzo)

The values used in this patch are taken from a SPSA parameter tuning session
originated by Unai Corzo (@unaiic), but the final difference of his tune was
multiplied x2 by hand. Most of the credits should go to him :-)

STC:
https://tests.stockfishchess.org/tests/view/602f03d07f517a561bc49d40
LLR: 2.94 (-2.94,2.94) {-0.25,1.25}
Total: 67664 W: 6252 L: 6035 D: 55377 Elo +1.11
Ptnml(0-2): 256, 4799, 23527, 4972, 278

LTC:
https://tests.stockfishchess.org/tests/view/602f41697f517a561bc49d5a
LLR: 2.96 (-2.94,2.94) {0.25,1.25}
Total: 26256 W: 1034 L: 906 D: 24316 Elo +1.69
Ptnml(0-2): 10, 804, 11377, 922, 15

Closes https://github.com/official-stockfish/Stockfish/pull/3363

Bench: 3957653
see source

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