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
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Disservin
Date: Mon Jan 1 02:31:25 2024 +0100
Timestamp: 1704072685

Fix formatting in search.cpp

fixes the formatting for 1fe562fdf32c153f82929660197f8b97469f76b4
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Stefan Geschwentner
Date: Sun Dec 31 20:09:09 2023 +0100
Timestamp: 1704049749

Tweak static eval history update

Modify the applied static eval bonus for main and pawn history with different
factors for positive and negative values.

Passed STC:
https://tests.stockfishchess.org/tests/view/659132e179aa8af82b957bb0
LLR: 2.93 (-2.94,2.94) <0.00,2.00>
Total: 12512 W: 3308 L: 3027 D: 6177 Elo +7.80
Ptnml(0-2): 32, 1372, 3189, 1609, 54

Passed LTC:
https://tests.stockfishchess.org/tests/view/65913e3d79aa8af82b957cd2
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 35946 W: 9128 L: 8809 D: 18009 Elo +3.08
Ptnml(0-2): 19, 3879, 9862, 4190, 23

closes https://github.com/official-stockfish/Stockfish/pull/4952

Bench: 1392883
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Michael Chaly
Date: Sun Dec 31 20:00:06 2023 +0100
Timestamp: 1704049206

Introduce static evaluation correction history

Idea from Caissa (https://github.com/Witek902/Caissa) chess engine.

With given pawn structure collect data with how often search result and by how
much it was better / worse than static evalution of position and use it to
adjust static evaluation of positions with given pawn structure. Details:

1. excludes positions with fail highs and moves producing it being a capture;
2. update value is function of not only difference between best value and static
evaluation but also is multiplied by linear function of depth;
3. maximum update value is maximum value of correction history divided by 2;
4. correction history itself is divided by 32 when applied so maximum value of
static evaluation adjustment is 32 internal units.

Passed STC:
https://tests.stockfishchess.org/tests/view/658fc7b679aa8af82b955cac
LLR: 2.96 (-2.94,2.94) <0.00,2.00>
Total: 128672 W: 32757 L: 32299 D: 63616 Elo +1.24
Ptnml(0-2): 441, 15241, 32543, 15641, 470

Passed LTC:
https://tests.stockfishchess.org/tests/view/65903f6979aa8af82b9566f1
LLR: 2.95 (-2.94,2.94) <0.50,2.50>
Total: 97422 W: 24626 L: 24178 D: 48618 Elo +1.60
Ptnml(0-2): 41, 10837, 26527, 11245, 61

closes https://github.com/official-stockfish/Stockfish/pull/4950

Bench: 1157852
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: FauziAkram
Date: Sun Dec 31 19:58:10 2023 +0100
Timestamp: 1704049090

Mark square_bb() as constexpr

closes https://github.com/official-stockfish/Stockfish/pull/4949

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
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: FauziAkram
Date: Sun Dec 31 19:57:34 2023 +0100
Timestamp: 1704049054

Simplify the improving flag calculation

Passed STC:
https://tests.stockfishchess.org/tests/view/658ec29979aa8af82b9547f6
LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 93408 W: 23747 L: 23587 D: 46074 Elo +0.60
Ptnml(0-2): 340, 11178, 23527, 11300, 359

Passed LTC:
https://tests.stockfishchess.org/tests/view/658f73e479aa8af82b9555b6
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 64026 W: 15984 L: 15806 D: 32236 Elo +0.97
Ptnml(0-2): 31, 7113, 17552, 7281, 36

closes https://github.com/official-stockfish/Stockfish/pull/4948

Bench: 1143749
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: FauziAkram
Date: Sun Dec 31 19:54:27 2023 +0100
Timestamp: 1704048867

Cleanup comments

Tests used to derive some Elo worth comments:
https://tests.stockfishchess.org/tests/view/656a7f4e136acbc573555a31
https://tests.stockfishchess.org/tests/view/6585fb455457644dc984620f

closes https://github.com/official-stockfish/Stockfish/pull/4945

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
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Tobias Steinmann
Date: Sun Dec 31 19:51:04 2023 +0100
Timestamp: 1704048664

Update Makefile for android x86-64 builds

For developing an Android GUI it can be helpful to use the Emulator on Windows.
Therefor an android_x86-64 library of Stockfish is needed. It would be nice to
compile it "out-of-the-box".

This change is originally suggested by Craftyawesome

closes https://github.com/official-stockfish/Stockfish/pull/4927

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
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Shahin M. Shahin
Date: Sat Dec 30 12:19:48 2023 +0100
Timestamp: 1703935188

Fix scores from reverse futility pruning

This fixes futility pruning return values after recent tweaks, `eval` is
guaranteed to be less than the mate-in range but it can be as low value such
that the average between eval and beta can still fall in the mated-in range when
beta is as low in mated range. i.e. (eval + beta) / 2 being at mated-range which
can break mates.

Passed non-regression STC:
https://tests.stockfishchess.org/tests/view/658f3eed79aa8af82b955139
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 117408 W: 29891 L: 29761 D: 57756 Elo +0.38
Ptnml(0-2): 386, 13355, 31120, 13429, 414

Passed non-regression LTC:
https://tests.stockfishchess.org/tests/view/658f8b7a79aa8af82b9557bd
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 60240 W: 14962 L: 14786 D: 30492 Elo +1.02
Ptnml(0-2): 22, 6257, 17390, 6425, 26

changes signature at higher depth e.g. `128 1 15`

closes https://github.com/official-stockfish/Stockfish/pull/4944

Bench: 1304666
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Linmiao Xu
Date: Sat Dec 30 11:08:03 2023 +0100
Timestamp: 1703930883

Update default net to nn-b1e55edbea57.nnue

Created by retraining the master big net `nn-0000000000a0.nnue` on the same
dataset with the ranger21 optimizer and more WDL skipping at training time.

More WDL skipping is meant to increase lambda accuracy and train on fewer
misevaluated positions where position scores are unlikely to correlate
with game outcomes. Inspired by:
- repeated reports in discord #events-discuss about SF misplaying due to wrong endgame
evals, possibly due to Leela's endgame weaknesses reflected in training data
- an attempt to reduce the skewed dataset piece count distribution where there
are much more positions with less than 16 pieces, since the target piece count
distribution in the trainer is symmetric around 16

The faster convergence seen with ranger21 is meant to:
- prune experiment ideas more quickly since fewer epochs are needed to reach elo maxima
- research faster potential trainings by shortening each run

```yaml
experiment-name: 2560-S7-Re-514G-ranger21-more-wdl-skip
training-dataset: /data/S6-514G.binpack
early-fen-skipping: 28

start-from-engine-test-net: True
nnue-pytorch-branch: linrock/nnue-pytorch/r21-more-wdl-skip

num-epochs: 1200
lr: 4.375e-4
gamma: 0.995
start-lambda: 1.0
end-lambda: 0.7
```

Experiment yaml configs converted to easy_train.sh commands with:
https://github.com/linrock/nnue-tools/blob/4339954/yaml_easy_train.py

Implementations based off of Sopel's NNUE training & experimentation log:
https://docs.google.com/document/d/1gTlrr02qSNKiXNZ_SuO4-RjK4MXBiFlLE6jvNqqMkAY
- Experiment 336 - ranger21 https://github.com/Sopel97/nnue-pytorch/tree/experiment_336
- Experiment 351 - more WDL skipping

The version of the ranger21 optimizer used is:
https://github.com/lessw2020/Ranger21/blob/b507df6/ranger21/ranger21.py

The dataset is the exact same as in:
https://github.com/official-stockfish/Stockfish/pull/4782

Local elo at 25k nodes per move:
nn-epoch619.nnue : 6.2 +/- 4.2

Passed STC:
https://tests.stockfishchess.org/tests/view/658a029779aa8af82b94fbe6
LLR: 2.93 (-2.94,2.94) <0.00,2.00>
Total: 46528 W: 11985 L: 11650 D: 22893 Elo +2.50
Ptnml(0-2): 154, 5489, 11688, 5734, 199

Passed LTC:
https://tests.stockfishchess.org/tests/view/658a448979aa8af82b95010f
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 265326 W: 66378 L: 65574 D: 133374 Elo +1.05
Ptnml(0-2): 153, 30175, 71254, 30877, 204

This was additionally tested with the latest DualNNUE and passed SPRTs:

Passed STC vs. https://github.com/official-stockfish/Stockfish/pull/4919
https://tests.stockfishchess.org/tests/view/658bcd5c79aa8af82b951846
LLR: 2.93 (-2.94,2.94) <0.00,2.00>
Total: 296128 W: 76273 L: 75554 D: 144301 Elo +0.84
Ptnml(0-2): 1223, 35768, 73617, 35979, 1477

Passed LTC vs. https://github.com/official-stockfish/Stockfish/pull/4919
https://tests.stockfishchess.org/tests/view/658c988d79aa8af82b95240f
LLR: 2.95 (-2.94,2.94) <0.50,2.50>
Total: 75618 W: 19085 L: 18680 D: 37853 Elo +1.86
Ptnml(0-2): 45, 8420, 20497, 8779, 68

closes https://github.com/official-stockfish/Stockfish/pull/4942

Bench: 1304666
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: FauziAkram
Date: Sat Dec 30 11:05:19 2023 +0100
Timestamp: 1703930719

Refactor bestvalue adjustment in qsearch

closes https://github.com/official-stockfish/Stockfish/pull/4935

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
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Michael Chaly
Date: Sat Dec 30 11:01:32 2023 +0100
Timestamp: 1703930492

Adjust value returned after TT cutoff

Instead of returning value from TT in case of a fail high return mix between it
and beta.

Passed STC:
https://tests.stockfishchess.org/tests/view/658465395457644dc98446c7
LLR: 2.93 (-2.94,2.94) <0.00,2.00>
Total: 220704 W: 56404 L: 55811 D: 108489 Elo +0.93
Ptnml(0-2): 750, 26214, 55921, 26627, 840

Passed LTC:
https://tests.stockfishchess.org/tests/view/6585c3f55457644dc9845db9
LLR: 2.97 (-2.94,2.94) <0.50,2.50>
Total: 124980 W: 31169 L: 30658 D: 63153 Elo +1.42
Ptnml(0-2): 57, 14147, 33603, 14594, 89

closes https://github.com/official-stockfish/Stockfish/pull/4934

Bench: 1191093
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: peregrineshahin
Date: Sat Dec 30 10:57:48 2023 +0100
Timestamp: 1703930268

Fix wrong mate/tb scores from probCut

This fixes returning wrong mated-in scores, or losing a proven mate-in score
from probCut after recent tweaks. The issue reported by @cj5716 on discord.

Passed non-reg STC:
https://tests.stockfishchess.org/tests/view/6583c36b5457644dc9843afe
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 295936 W: 75011 L: 75075 D: 145850 Elo -0.08
Ptnml(0-2): 978, 33947, 78146, 33955, 942

Passed non-reg LTC:
https://tests.stockfishchess.org/tests/view/658513075457644dc98451cd
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 55932 W: 13970 L: 13786 D: 28176 Elo +1.14
Ptnml(0-2): 33, 5933, 15837, 6143, 20

closes https://github.com/official-stockfish/Stockfish/pull/4933

Bench: 1308739
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: FauziAkram
Date: Fri Dec 22 11:51:08 2023 +0100
Timestamp: 1703242268

Tweak quiet move bonus

Improving quiet move bonus by replacing bestvalue and alpha comparison, with
checking the statScore of the previous search step instead.

Inspired by @locutus2

Passed STC:
https://tests.stockfishchess.org/tests/view/657f22fb893104ee25b614e8
LLR: 2.96 (-2.94,2.94) <0.00,2.00>
Total: 51296 W: 13121 L: 12774 D: 25401 Elo +2.35
Ptnml(0-2): 225, 5986, 12868, 6355, 214

Passed LTC:
https://tests.stockfishchess.org/tests/view/658024a2893104ee25b62587
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 82758 W: 20606 L: 20189 D: 41963 Elo +1.75
Ptnml(0-2): 51, 9149, 22555, 9580, 44

closes https://github.com/official-stockfish/Stockfish/pull/4930

Bench: 1312822
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Disservin
Date: Fri Dec 22 11:48:43 2023 +0100
Timestamp: 1703242123

Revert "Adjust stand pat in qsearch on pv nodes"

This reverts commit d9ec82e7438716671168d78eee26fae327249e8c.

Bench: 1249544
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Michael Chaly
Date: Tue Dec 19 18:22:10 2023 +0100
Timestamp: 1703006530

Adjust return value in qsearch after fail high

Instead of returning strict fail soft fail high return value between value from
search and beta (somewhat by analogy to futility pruning and probcut).

This seems to be somewhat depth sensitive heuristic which performed much worse
at LTC while performing much better at STC if it is more aggressive, passed
version is the least aggressive one.

Passed STC:
https://tests.stockfishchess.org/tests/view/657b06414d789acf40ab1475
LLR: 2.95 (-2.94,2.94) <0.00,2.00>
Total: 212352 W: 53900 L: 53315 D: 105137 Elo +0.96
Ptnml(0-2): 809, 25236, 53520, 25783, 828

Passed LTC:
https://tests.stockfishchess.org/tests/view/657ce36f393ac02e79120a7c
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 319362 W: 79541 L: 78630 D: 161191 Elo +0.99
Ptnml(0-2): 202, 35839, 86709, 36708, 223

closes https://github.com/official-stockfish/Stockfish/pull/4928

Bench: 974739
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: FauziAkram
Date: Tue Dec 19 18:22:10 2023 +0100
Timestamp: 1703006530

Use std::abs over abs

closes https://github.com/official-stockfish/Stockfish/pull/4926
closes https://github.com/official-stockfish/Stockfish/pull/4909

No functional change

Co-Authored-By: fffelix-huang <72808219+>
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: FauziAkram
Date: Tue Dec 19 18:22:10 2023 +0100
Timestamp: 1703006530

Improvement of Time Management Parameters

Passed STC:
https://tests.stockfishchess.org/tests/view/6579c5574d789acf40aaf914
LLR: 2.93 (-2.94,2.94) <0.00,2.00>
Total: 44672 W: 11354 L: 11030 D: 22288 Elo +2.52
Ptnml(0-2): 140, 5033, 11685, 5319, 159

Passed LTC:
https://tests.stockfishchess.org/tests/view/657ad7f44d789acf40ab105e
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 40932 W: 10275 L: 9950 D: 20707 Elo +2.76
Ptnml(0-2): 21, 4316, 11473, 4629, 27

Passed non-regression Sudden death 10+0:
https://tests.stockfishchess.org/tests/view/657b9b9e393ac02e7911f1a8
LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 21384 W: 5171 L: 4925 D: 11288 Elo +4.00
Ptnml(0-2): 112, 2420, 5409, 2612, 139

closes https://github.com/official-stockfish/Stockfish/pull/4923

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
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Michael Chaly
Date: Tue Dec 19 18:22:10 2023 +0100
Timestamp: 1703006530

Adjust stand pat in qsearch on pv nodes

Instead of immediately returning a fail high do this only at non-pv nodes, for
pv nodes adjust bestValue to value between alpha and beta and continue
searching. Idea is to do it the same way as it's done in search where we don't
return positive beta cutoffs after ttHits / zero window search at PvNodes and
instead fully search lines.

Passed STC:
https://tests.stockfishchess.org/tests/view/65739b0af09ce1261f122f33
LLR: 2.94 (-2.94,2.94) <0.00,2.00>
Total: 189216 W: 48142 L: 47598 D: 93476 Elo +1.00
Ptnml(0-2): 584, 22463, 48051, 22845, 665

Passed LTC:
https://tests.stockfishchess.org/tests/view/657701214d789acf40aac194
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 82506 W: 20689 L: 20269 D: 41548 Elo +1.77
Ptnml(0-2): 56, 9236, 22268, 9618, 75

Two issues had to be resolved:
- in rare cases it set alpha to the same value as beta and thus broke some asserts;
- messed up with returning tb win values.

Fix passed non-regression LTC vs this patch:
https://tests.stockfishchess.org/tests/view/6578113b4d789acf40aad544
LLR: 2.96 (-2.94,2.94) <-1.75,0.25>
Total: 277308 W: 68839 L: 68880 D: 139589 Elo -0.05
Ptnml(0-2): 167, 31580, 75212, 31517, 178

closes https://github.com/official-stockfish/Stockfish/pull/4922

Bench: 1069503

Co-Authored-By: Muzhen Gaming <61100393+>
Co-Authored-By: Shahin M. Shahin <41402573+>
Co-Authored-By: fffelix-huang <72808219+>
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Muzhen Gaming
Date: Thu Dec 14 18:50:51 2023 +0100
Timestamp: 1702576251

Remove UCI_AnalyseMode Option

Simplify away the useless option, as documented: "An option handled by your GUI.
This currently doesn't do anything."

The option was originally added with the introduction of contempt
(https://github.com/official-stockfish/Stockfish/commit/e9aeaad05266ca557a9496b5a17b4c5f82f0e946),
but it is now no longer used.

closes https://github.com/official-stockfish/Stockfish/pull/4918

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
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: FauziAkram
Date: Thu Dec 14 18:44:46 2023 +0100
Timestamp: 1702575886

Remove SlowMover Option

The SlowMover option allows users to modify the timeLeft variant, impacting the
engine's time management. However, this feature, while theoretically flexible,
doesn't offer substantial benefits. Instead, it introduces the risk of
non-experienced users altering values without a clear understanding of the
effects, potentially leading to a weaker engine.

The vast majority of SF users don't use it anyway, and based on tests conducted
by fauzi several months ago suggest that changing it would only lose Elo.

Examples:
https://tests.stockfishchess.org/tests/view/651f309bac57711436726bba
https://tests.stockfishchess.org/tests/view/651fea29ac57711436727d85
https://tests.stockfishchess.org/tests/view/65257c343125598fc7eb68a1
https://tests.stockfishchess.org/tests/view/652296c83125598fc7eb2ad7
Tune:
https://tests.stockfishchess.org/tests/view/652a70313125598fc7ebd706
(keeping the value at 100, zz2)

closes https://github.com/official-stockfish/Stockfish/pull/4917

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
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Disservin
Date: Thu Dec 14 18:43:02 2023 +0100
Timestamp: 1702575782

Fix action deprecation warning for dev-drprasad

closes https://github.com/official-stockfish/Stockfish/pull/4914

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
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: WangXiang
Date: Thu Dec 14 18:41:53 2023 +0100
Timestamp: 1702575713

Add loongarch64 support

Adding support for LoongArch64 architecture. Tested on Loongson 3A6000 EVB
Board. Since Loongson's SIMD extended instruction set
([LSX](https://gcc.gnu.org/onlinedocs/gcc/LoongArch-SX-Vector-Intrinsics.html),
[LASX](https://gcc.gnu.org/onlinedocs/gcc/LoongArch-ASX-Vector-Intrinsics.html))
is already supported by GCC, more optimizations are being developed.

Here's the benchmark result for Loongson 3A6000 (4c8t, 2.5Ghz) without SIMD
optimizations.
```
Total time (ms) : 17903
Nodes searched : 1244386
Nodes/second : 69507
```

closes https://github.com/official-stockfish/Stockfish/pull/4913

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
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: peregrineshahin
Date: Thu Dec 14 18:36:45 2023 +0100
Timestamp: 1702575405

Track seldepth in qsearch too

Sometimes if we count the reported PV length, it turns out to be longer than the
selective depth reported. This fixes this behavior by applying the selective
depth to qsearch since we do report PVs from it as well.

Passed non-regression STC:
https://tests.stockfishchess.org/tests/view/656cf5b66980e15f69c7499d
LLR: 2.96 (-2.94,2.94) <-1.75,0.25>
Total: 223648 W: 56372 L: 56356 D: 110920 Elo +0.02
Ptnml(0-2): 710, 25580, 59231, 25590, 713

closes https://github.com/official-stockfish/Stockfish/pull/4903

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
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Shahin M. Shahin
Date: Thu Dec 14 18:35:38 2023 +0100
Timestamp: 1702575338

Fix TB score output in UCI without using TB

This is a rewrite of the fix introduced for
https://github.com/official-stockfish/Stockfish/issues/4413 in
https://github.com/official-stockfish/Stockfish/pull/4591 by @windfishballad it
targets only the relevant part of this issue that returns TB scores (CP 20000)
without using TB due to the downgrading of potentially false mates from the TT
to an optimal TB score.

the difference is that it is a much clearer code that introduces a separate
TB_VALUE constant to account for a correct distance from the TB_VALUE with
MAX_PLY.

the originally posted position in the issue does not trigger the problem
anymore, so here is a new position to test:
```
position fen 3k4/8/8/8/8/8/3BN3/3K4 w - - 0 1
go infinite
```

Passed non-regression STC:
https://tests.stockfishchess.org/tests/view/65578994136acbc57353b258
LLR: 2.96 (-2.94,2.94) <-1.75,0.25>
Total: 119264 W: 29993 L: 29863 D: 59408 Elo +0.38
Ptnml(0-2): 372, 13692, 31379, 13812, 377

Passed non-regression LTC:
https://tests.stockfishchess.org/tests/view/6558323f136acbc57353c1ca
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 237834 W: 58791 L: 58792 D: 120251 Elo -0.00
Ptnml(0-2): 193, 26200, 66111, 26241, 172

fixes https://github.com/official-stockfish/Stockfish/issues/4413
closes https://github.com/official-stockfish/Stockfish/pull/4591
closes https://github.com/official-stockfish/Stockfish/pull/4882

Bench: 1305821
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers + AVX2
Windows x64 for modern computers
Windows x64 + SSSE3
Windows x64
Linux x64 for Haswell CPUs
Linux x64 for modern computers + AVX2
Linux x64 for modern computers
Linux x64 + SSSE3
Linux x64
Author: Muzhen Gaming
Date: Sun Dec 10 23:23:28 2023 +0100
Timestamp: 1702247008

VLTC Search parameters tune

The SPSA tuning was done for 44k games at 120+1.2.
https://tests.stockfishchess.org/tests/view/656ee2a76980e15f69c7767f.

Note that the tune was originally done in combination with the recent dual NNUE
idea (see #4910).

VLTC:
https://tests.stockfishchess.org/tests/view/65731ccbf09ce1261f12246e
LLR: 2.95 (-2.94,2.94) <0.00,2.00>
Total: 52806 W: 13069 L: 12760 D: 26977 Elo +2.03
Ptnml(0-2): 19, 5498, 15056, 5815, 15

VLTC SMP:
https://tests.stockfishchess.org/tests/view/65740ffaf09ce1261f1239ba
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 27630 W: 6934 L: 6651 D: 14045 Elo +3.56
Ptnml(0-2): 1, 2643, 8243, 2928, 0

Estimated close to neutral at LTC:
https://tests.stockfishchess.org/tests/view/6575485a8ec68176cf7d9423
Elo: -0.59 ± 1.8 (95%) LOS: 26.6%
Total: 32060 W: 7859 L: 7913 D: 16288 Elo -0.59
Ptnml(0-2): 20, 3679, 8676, 3645, 10
nElo: -1.21 ± 3.8 (95%) PairsRatio: 0.99

closes https://github.com/official-stockfish/Stockfish/pull/4912

Bench: 1283323
see source

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