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: SFisGOD
Date: Sat Nov 2 21:19:35 2019 +0100
Timestamp: 1572725975

Combo of Parameter Tweaks

This patch is a combo of the following tweaks:

Complexity parameters
Knight PSQT
Bishop PSQT
King PSQT
Piece Values

Passed STC:
LLR: 2.95 (-2.94,2.94) [-1.50,4.50]
Total: 56527 W: 12326 L: 12052 D: 32149 Elo +1.68
http://tests.stockfishchess.org/tests/view/5dbbca3f0ebc5925b64ee6d6

Passed LTC:
LLR: 2.95 (-2.94,2.94) [0.00,3.50]
Total: 64010 W: 10549 L: 10199 D: 43262 Elo +1.90
http://tests.stockfishchess.org/tests/view/5dbc30dc0ebc5925b64eee0c

Closes https://github.com/official-stockfish/Stockfish/pull/2390

Bench: 4312945
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: Thu Oct 31 17:47:23 2019 +0100
Timestamp: 1572540443

Simplify kingRing

Simplify the king ring initialization and make it more regular, by just
moving the king square off the edges and using PseudoAttacks by king from
this new square.

There is a small functional difference from the previous master, as the
old master excludes the original ksq square while this patch always includes
the nine squares block (after moving the king from the edges). Additionally,
master does not adjust the kingRing down if we are on relative rank 8,
while this patch treats all of the edges the same.

STC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 13263 W: 2968 L: 2830 D: 7465 Elo +3.62
http://tests.stockfishchess.org/tests/view/5db872830ebc5902d1f388aa

LTC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 72996 W: 11819 L: 11780 D: 49397 Elo +0.19
http://tests.stockfishchess.org/tests/view/5db899c20ebc5902d1f38b5e

Closes https://github.com/official-stockfish/Stockfish/pull/2384

Bench: 4959244
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: Thu Oct 31 17:22:09 2019 +0100
Timestamp: 1572538929

Consolidate pawn_push and up

This is a non-functional simplification. Pawn_push and Up are redundant.
If we make up pawn_push, we can use it for all of the Up's and Down's.
In this version, I've also left the Up and Down constants so that there
is no worse readability.

STC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 23878 W: 5202 L: 5085 D: 13591 Elo +1.70
http://tests.stockfishchess.org/tests/view/5db5569a0ebc5902d6b14de4

Closes https://github.com/official-stockfish/Stockfish/pull/2378

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: Stefan Geschwentner
Date: Thu Oct 31 17:05:29 2019 +0100
Timestamp: 1572537929

Tweak dynamic contempt (the birthday patch)

Make dynamic contempt weight factor dependent on static contempt so that higher
static contempt implies less dynamic contempt and vice versa. For default contempt
24 this is a non-functional change. But tests with contempt 0 shows an elo gain.
Also today is my birthday so i have already give to myself a gift with this patch :-)!

Further proceedings:

in the past we checked for default contempt that it doesn't regress against
contempt 0. Now that the later is stronger and the former is the same strength
this should be rechecked. Perhaps the default contempt have to be lowered.
It would be interesting to get some idea of the impact of this patch outside
of the 0-24 contempt range.

STC: (both with contempt=0)
LLR: 2.95 (-2.94,2.94) [-1.50,4.50]
Total: 21912 W: 3898 L: 3740 D: 14274 Elo +2.51
http://tests.stockfishchess.org/tests/view/5db74b6f0ebc5902d1f37405

LTC: (both with contempt=0)
LLR: 2.96 (-2.94,2.94) [0.00,3.50]
Total: 27172 W: 3350 L: 3126 D: 20696 Elo +2.86
http://tests.stockfishchess.org/tests/view/5db760020ebc5902d1f375d0

Closes https://github.com/official-stockfish/Stockfish/pull/2382

No functional change (for current default contempt 24).
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
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Windows 32
Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: Joost VandeVondele
Date: Sat Oct 26 01:10:55 2019 +0200
Timestamp: 1572045055

Refactor final stats updates.

This PR refactors update_quiet_stats, update_capture_stats and search to more clearly reflect what is actually done.

Effectively, all stat updates that need to be done after search is finished and a bestmove is found,
are collected in a new function ```final_stats_update()```. This shortens our main search routine, and simplifies ```update_quiet_stats```.
The latter function is now more easily reusable with fewer arguments, as the handling of ```quietsSearched``` is only needed in ```final_stats_update```.
```update_capture_stats```, which was only called once is now integrated in ```final_stats_update```, which allows for removing a branch and reusing some ```stat_bonus``` calls. The need for refactoring was also suggested by the fact that the comments of ```update_quiet_stats``` and ```update_capture_stats``` were incorrect (e.g. ```update_capture_stats``` was called, correctly, also when the bestmove was a quiet and not a capture).

passed non-regression STC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 75196 W: 16364 L: 16347 D: 42485 Elo +0.08
http://tests.stockfishchess.org/tests/view/5db004ec0ebc5902c06db9e1

The diff is most easily readable as ```git diff master --patience```

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: Stéphane Nicolet
Date: Sat Oct 26 00:29:12 2019 +0200
Timestamp: 1572042552

Assorted trivial cleanups

- Cleanups by Alain
- Group king attacks and king defenses
- Signature of futility_move_count()
- Use is_discovery_check_on_king()
- Simplify backward definition
- Use static asserts in move generator
- Factor a statement in move generator

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: Joost VandeVondele
Date: Wed Oct 23 10:49:08 2019 +0200
Timestamp: 1571820548

Simplify reductions on singular extension

Current master employs a scheme to adjust reductions on singular
nodes that is somewhat controversial, see
https://github.com/official-stockfish/Stockfish/pull/2167

This patch removes this use of a search result outside of [a,b],
by observing that the main effect of this code is to adjust the
reduction by an average of ~2 (1.7) rather than 1.

Claims the first blue at STC and LTC:

STC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 30142 W: 6547 L: 6442 D: 17153 Elo +1.21
http://tests.stockfishchess.org/tests/view/5daf16c40ebc5902c06da566

LTC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 45715 W: 7380 L: 7298 D: 31037 Elo +0.62
http://tests.stockfishchess.org/tests/view/5daf2f3c0ebc5902c06da6c7

Closes https://github.com/official-stockfish/Stockfish/pull/2367

Bench: 5115841
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: Tue Oct 22 00:02:46 2019 +0200
Timestamp: 1571695366

Avoid crashing on Log File opening

Stockfish crashes immediately if users enter a wrong file name (or even an existing
folder name) for debug log file. It may be hard for users to find out since it prints
nothing. If they enter the string via a chess GUI, the chess GUI may remember and
auto-send to Stockfish next time, makes Stockfish crashes all the time. Bug report by
Nguyen Hong Pham in this issue: https://github.com/official-stockfish/Stockfish/issues/2365

This patch avoids the crash and instead prefers to exit gracefully with a error
message on std:cerr, like we do with the fenFile for instance.

Closes https://github.com/official-stockfish/Stockfish/pull/2366

No functional change.
see source
Windows x64 for Haswell CPUs
Windows x64 for modern computers
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Linux x64 for Haswell CPUs
Linux x64 for modern computers
Linux x64
Author: xoto10
Date: Sun Oct 20 00:27:17 2019 +0200
Timestamp: 1571524037

Remove uithread

With the current questions and issues around threading, I had a look at
https://github.com/official-stockfish/Stockfish/issues/2299.

It seems there was a problem with data races when requesting eval via UCI while
a search was already running. To fix this an extra thread uithread was created,
presumably to avoid an overlap with Threads.main() that was causing problems.
Making this eval request seems to be outside the scope of UCI, and @vondele also
reports that the data race is not even fixed reliably by this change. I suggest
we simplify the threading here by removing this uithread and adding a comment
signaling that user should not request eval when a search is already running.

Closes https://github.com/official-stockfish/Stockfish/pull/2310

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: VoyagerOne
Date: Fri Oct 18 17:05:23 2019 +0200
Timestamp: 1571411123

Current capture for Counter-Move history

Use current capture to index the CMH table instead of prior capture.

STC:
LLR: 2.96 (-2.94,2.94) [0.00,4.00]
Total: 61908 W: 13626 L: 13220 D: 35062 Elo +2.28
http://tests.stockfishchess.org/tests/view/5da8aa670ebc597ba8eda558

LTC:
LLR: 2.96 (-2.94,2.94) [0.00,4.00]
Total: 49057 W: 8071 L: 7765 D: 33221 Elo +2.17
http://tests.stockfishchess.org/tests/view/5da8e99d0ebc597ba8eda9ca

Closes https://github.com/official-stockfish/Stockfish/pull/2362

Bench: 4423737
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 Oct 17 15:03:30 2019 +0200
Timestamp: 1571317410

Add four positions to bench

The current bench is missing a position with high 50 moves rule counter,
making most 'shuffle' tests based on 50mr > N seem non-functional.
This patch adds one FEN with high 50mr counter to address this issue
(taken from a recent tcec game).

Four new FENs:
- position with high 50mr counter
- tactical position with many captures, checks, extensions, fails high/low
- two losses by Stockfish in the S16 bonus games against Houdini

See the pull request for nice comments by @Alayan-stk-2 about each position
in bench: https://github.com/official-stockfish/Stockfish/pull/2338

Bench: 4590210
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: VoyagerOne
Date: Wed Oct 9 15:22:16 2019 +0900
Timestamp: 1570602136

Introduce separate counter-move tables for inCheck

Enhance counter-move history table by adding a inCheck dimension. This doubles
the size of the table but provides more accurate move ordering.

STC: (yellow)
LLR: -2.94 (-2.94,2.94) [0.50,4.50]
Total: 36217 W: 7790 L: 7777 D: 20650 Elo +0.12
http://tests.stockfishchess.org/tests/view/5d9b9a290ebc5902b6d04fe0

LTC:
LLR: 2.95 (-2.94,2.94) [0.00,3.50]
Total: 36665 W: 6063 L: 5788 D: 24814 Elo +2.61
http://tests.stockfishchess.org/tests/view/5d9b9fcc0ebc5902b6d05985

Closes https://github.com/official-stockfish/Stockfish/pull/2353

Bench: 4053577
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: 31m059
Date: Wed Oct 9 14:17:52 2019 +0900
Timestamp: 1570598272

No reachable outpost bonus for bishops

Previously, we used various control statements and ternary operators to divide
Outpost into four bonuses, based on whether the outpost was for a knight or
bishop, and whether it was currently an Outpost or merely a potential ("reachable")
one in the future. Bishop outposts, however, have traditionally been worth far
less Elo in testing. An attempt to remove them altogether passed STC, but failed LTC.

Here we include a narrower simplification, removing the reachable Outpost bonus
for bishops. This bonus was always suspect, given that its current implementation
conflicts directly with BishopPawns. BishopPawns penalizes our bishops based on the
number of friendly pawns on the same color of square, but by definition, Outposts
must be pawn-protected! This PR helps to alleviate this conceptual contradiction
without loss of Elo and with slightly simpler code.

On a code level, this allows us to simplify a ternary operator into the previous
"if" block and distribute a multiplication into an existing constant Score. On a
conceptual level, we retire one of the four traditional Outpost bonuses.

STC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 22277 W: 4882 L: 4762 D: 12633 Elo +1.87
http://tests.stockfishchess.org/tests/view/5d9aeed60ebc5902b6cf9751

LTC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 51206 W: 8353 L: 8280 D: 34573 Elo +0.50
http://tests.stockfishchess.org/tests/view/5d9af1940ebc5902b6cf9cd5

Closes https://github.com/official-stockfish/Stockfish/pull/2352

Bench: 3941591
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: Alayan
Date: Mon Oct 7 22:30:04 2019 +0200
Timestamp: 1570480204

Adjust aspiration window with eval

This patch changes the base aspiration window size depending on the absolute
value of the previous iteration score, increasing it away from zero. This
stems from the observation that the further away from zero, the more likely
the evaluation is to change significantly with more depth. Conversely, a
tighter aspiration window is more efficient when close to zero.

A beneficial side-effect is that analysis of won positions without a quick
mate is less prone to waste nodes in repeated fail-high that change the eval
by tiny steps.

STC:
LLR: 2.96 (-2.94,2.94) [0.50,4.50]
Total: 60102 W: 13327 L: 12868 D: 33907 Elo +2.65
http://tests.stockfishchess.org/tests/view/5d9a70d40ebc5902b6cf39ba

LTC:
LLR: 2.95 (-2.94,2.94) [0.00,3.50]
Total: 155553 W: 25745 L: 25141 D: 104667 Elo +1.35
http://tests.stockfishchess.org/tests/view/5d9a7ca30ebc5902b6cf4028

Future work : the values used in this patch were only a reasonable guess.
Further testing should unveil more optimal values. However, the aspiration
window is rather tight with a minimum of 21 internal units, so discrete
integers put a practical limitation to such tweaking.

More exotic experiments around the aspiration window parameters could also
be tried, but efficient conditions to adjust the base aspiration window size
or allow it to not be centered on the current evaluation are not obvious.

The aspiration window increases after a fail-high or a fail-low is another
avenue to explore for potential enhancements.

Bench: 4043748
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: SFisGOD
Date: Mon Oct 7 11:14:33 2019 +0200
Timestamp: 1570439673

Tweak kingFlankAttacks factor in kingDanger

Increase kingFlankAttacks factor in kingDanger from 5/16 to 6/16.

Failed STC:
LLR: -2.96 (-2.94,2.94) [0.00,4.00]
Total: 77947 W: 16989 L: 16848 D: 44110 Elo +0.63
http://tests.stockfishchess.org/tests/view/5d9ac0280ebc5902b6cf63cd

Passed LTC 1:
LLR: 2.96 (-2.94,2.94) [0.00,4.00]
Total: 13443 W: 2231 L: 2037 D: 9175 Elo +5.01
http://tests.stockfishchess.org/tests/view/5d9ac88d0ebc5902b6cf6ffb

Passed LTC 2:
LLR: 2.96 (-2.94,2.94) [0.00,4.00]
Total: 23340 W: 3842 L: 3617 D: 15881 Elo +3.35
http://tests.stockfishchess.org/tests/view/5d9acf7f0ebc5902b6cf7c27

Closes https://github.com/official-stockfish/Stockfish/pull/2349

Bench: 4042155
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: Alain SAVARD
Date: Mon Oct 7 00:50:54 2019 +0200
Timestamp: 1570402254

Adjust pawn span

Run as a simplification

a) insures that pawn attacks are always included in the pawn span
(this "fixes" the case where some outpost or reachable outpost
bonus were awarded on squares controlled by enemy pawns).

b) compute the full span only if not "backward" or not "blocked".

By looking at "blocked" instead of "opposed", we get a nice simpli-
fication and the "new" outpost detection is almost identical, except
a few borderline cases on rank 4.

passed STC
http://tests.stockfishchess.org/tests/view/5d9950730ebc5902b6cefb90
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 79113 W: 17168 L: 17159 D: 44786 Elo +0.04

passed LTC
http://tests.stockfishchess.org/tests/view/5d99d14e0ebc5902b6cf0692
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 41286 W: 6819 L: 6731 D: 27736 Elo +0.74

See https://github.com/official-stockfish/Stockfish/pull/2348

bench: 3812891
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: Ondrej Mosnacek
Date: Sun Oct 6 23:05:30 2019 +0200
Timestamp: 1570395930

Make priorCapture a bool

It is always used as a bool, so let's make it a bool straight away.
We can always redefine it as a Piece in a later patch if we want
to use the piece type or the piece color.

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: VoyagerOne
Date: Sun Oct 6 02:04:19 2019 +0200
Timestamp: 1570320259

Introduce separate counter-move tables for captures

Enhance counter-move history table by adding a capture/no-capture dimension,
depending wether the previous move was a quiet move or a capture. This doubles
the size of the table but provides more accurate move ordering.

STC:
LLR: 2.95 (-2.94,2.94) [0.50,4.50]
Total: 79702 W: 17720 L: 17164 D: 44818 Elo +2.42
http://tests.stockfishchess.org/tests/view/5d97945e0ebc590c21aa724b

LTC:
LLR: 2.96 (-2.94,2.94) [0.00,3.50]
Total: 29147 W: 4907 L: 4651 D: 19589 Elo +3.05
http://tests.stockfishchess.org/tests/view/5d97ccb90ebc590c21aa7bc0

Closes https://github.com/official-stockfish/Stockfish/pull/2344

Bench: 4131643
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: Brian Sheppard
Date: Sun Oct 6 00:57:00 2019 +0200
Timestamp: 1570316220

Eliminate ONE_PLY

Simplification that eliminates ONE_PLY, based on a suggestion in the forum that
support for fractional plies has never been used, and @mcostalba's openness to
the idea of eliminating it. We lose a little bit of type safety by making Depth
an integer, but in return we simplify the code in search.cpp quite significantly.

No functional change

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

The argument favoring eliminating ONE_PLY:

* The term “ONE_PLY” comes up in a lot of forum posts (474 to date)
https://groups.google.com/forum/?fromgroups=#!searchin/fishcooking/ONE_PLY%7Csort:relevance

* There is occasionally a commit that breaks invariance of the code
with respect to ONE_PLY
https://groups.google.com/forum/?fromgroups=#!searchin/fishcooking/ONE_PLY%7Csort:date/fishcooking/ZIPdYj6k0fk/KdNGcPWeBgAJ

* To prevent such commits, there is a Travis CI hack that doubles ONE_PLY
and rechecks bench

* Sustaining ONE_PLY has, alas, not resulted in any improvements to the
engine, despite many individuals testing many experiments over 5 years.

The strongest argument in favor of preserving ONE_PLY comes from @locutus:
“If we use par example ONE_PLY=256 the parameter space is increases by the
factor 256. So it seems very unlikely that the optimal setting is in the
subspace of ONE_PLY=1.”

There is a strong theoretical impediment to fractional depth systems: the
transposition table uses depth to determine when a stored result is good
enough to supply an answer for a current search. If you have fractional
depths, then different pathways to the position can be at fractionally
different depths.

In the end, there are three separate times when a proposal to remove ONE_PLY
was defeated by the suggestion to “give it a few more months.” So… it seems
like time to remove this distraction from the community.

See the pull request here:
https://github.com/official-stockfish/Stockfish/pull/2289
see source
Windows x64 for Haswell CPUs
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Linux x64 for modern computers
Linux x64
Author: Stéphane Nicolet
Date: Sat Oct 5 11:15:24 2019 +0200
Timestamp: 1570266924

Fix compare function in previous patch

Bench: 4012371
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: mstembera
Date: Sat Oct 5 10:45:37 2019 +0200
Timestamp: 1570265137

Remove temporary shelter array

Remove temporary array of shelters and avoid iterating over it each time to find
if the shelter values after castling are better than the current value.
Work done on top of https://github.com/official-stockfish/Stockfish/pull/2277

Speed benchmark did not measure any difference.

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: Moez Jellouli
Date: Wed Oct 2 13:37:00 2019 +0200
Timestamp: 1570016220

More accurate pawn attack span definition

Tweak the pawn attack span for backward pawns and the zone behind
opponent opposing pawns. This is important in positional play and
one of weaknesses of the engine in recent high level games.

STC
LLR: -2.95 (-2.94,2.94) [0.50,4.50]
Total: 66843 W: 14884 L: 14717 D: 37242 Elo +0.87
http://tests.stockfishchess.org/tests/view/5d8dcb1b0ebc590f3beb2956

LTC
LLR: 2.96 (-2.94,2.94) [0.00,3.50]
Total: 77699 W: 12993 L: 12602 D: 52104 Elo +1.75
http://tests.stockfishchess.org/tests/view/5d8de9bc0ebc590f3beb3d00

See discussion in https://github.com/official-stockfish/Stockfish/pull/2332

Bench: 4012371
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 Oct 2 01:43:02 2019 +0200
Timestamp: 1569973382

Adjust reductions based on the number of threads

In lazySMP it makes sense to prune a little more, as multiple threads
search wider. We thus increase the prefactor of the reductions slowly
as a function of the threads. The prefactor of the log(threads) term
is a parameter, this pull request uses 1/2 after testing.

passed STC @ 8threads:
LLR: 2.96 (-2.94,2.94) [0.50,4.50]
Total: 118125 W: 23151 L: 22462 D: 72512 Elo +2.03
http://tests.stockfishchess.org/tests/view/5d8bbf4d0ebc59509180f217

passed LTC @ 8threads:
LLR: 2.95 (-2.94,2.94) [0.00,3.50]
Total: 67546 W: 10630 L: 10279 D: 46637 Elo +1.81
http://tests.stockfishchess.org/tests/view/5d8c463b0ebc5950918167e8

passed ~LTC @ 14threads:
LLR: 2.95 (-2.94,2.94) [0.00,3.50]
Total: 74271 W: 12421 L: 12040 D: 49810 Elo +1.78
http://tests.stockfishchess.org/tests/view/5d8db1f50ebc590f3beb24ef

Note:
A larger prefactor (1) passed similar tests at STC and LTC (8 threads),
while a very large one (2) passed STC quickly but failed LTC (8 threads).

For the single-threaded case there is no functional change.

Closes https://github.com/official-stockfish/Stockfish/pull/2337

Bench: 4088701

Fixup: remove redundant code.
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: Tue Oct 1 09:12:57 2019 +0200
Timestamp: 1569913977

Remove ThreatByRank

This is a functional simplification that removes ThreatByRank.

STC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 48009 W: 10630 L: 10560 D: 26819 Elo +0.51
http://tests.stockfishchess.org/tests/view/5d92095c0ebc594fb88eb61e

LTC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 18682 W: 3177 L: 3053 D: 12452 Elo +2.31
http://tests.stockfishchess.org/tests/view/5d9231120ebc594fb88ebacd

Moving forward, it's possible that ThreatByMinor and ThreatByRook
could be combined, but I haven't really contemplated that yet.

Closes https://github.com/official-stockfish/Stockfish/pull/2336

bench 4088701
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: Mon Sep 30 10:16:43 2019 +0200
Timestamp: 1569831403

Remove depth dependence in value_draw().

The condition "depth >= 4 * ONE_PLY" does not seem needed at this point.

passed STC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 32751 W: 7178 L: 7078 D: 18495 Elo +1.06
http://tests.stockfishchess.org/tests/view/5d8e46660ebc590f3bebad5e

passed LTC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 31693 W: 5299 L: 5196 D: 21198 Elo +1.13
http://tests.stockfishchess.org/tests/view/5d8e4b4f0ebc590f3bebb165

Bench: 4062526
see source

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