-removes wideUnsafeSquares bitboard
-removes a couple of bitboard operations
-removes one if operator
-updates comments so they actually represent what this part of code is doing now.
passed non-regression STC
http://tests.stockfishchess.org/tests/view/5d0c1ae50ebc5925cf0aa8db
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 16892 W: 3865 L: 3733 D: 9294
No functional change
Use comparison of eval with beta to predict potential cutNodes. This
allows multi-cut pruning to also prune possibly mislabeled Pv and NonPv
nodes.
STC:
LLR: 2.95 (-2.94,2.94) [0.50,4.50]
Total: 54305 W: 12302 L: 11867 D: 30136
http://tests.stockfishchess.org/tests/view/5d048ba50ebc5925cf0a15e8
LTC:
LLR: 2.95 (-2.94,2.94) [0.00,3.50]
Total: 189512 W: 32620 L: 31904 D: 124988
http://tests.stockfishchess.org/tests/view/5d04bf740ebc5925cf0a17f0
Normally I would think such changes are risky, specially for PvNodes,
but after trying a few other versions, it seems this version is more
sound than I initially thought.
Aside from this, a small funtional change is made to return
singularBeta instead of beta to be more consistent with the fail-soft
logic used in other parts of search.
=============================
How to continue from there ?
We could try to audit other parts of the search where the "cutNode"
variable is used, and try to use dynamic info based on heuristic
eval rather than on this variable, to check if the idea behind this
patch could also be applied successfuly.
Bench: 3503788
Fixes issues #2126 and #2189 where no progress in rootDepth is made for particular fens:
8/8/3P3k/8/1p6/8/1P6/1K3n2 b - - 0 1
8/1r1rp1k1/1b1pPp2/2pP1Pp1/1pP3Pp/pP5P/P5K1/8 w - - 79 46
the cause are the shuffle extensions. Upon closer analysis, it appears that in these cases a shuffle extension is made for every node searched, and progess can not be made. This patch implements a fix, namely to limit the number of extensions relative to the number of nodes searched. The ratio employed is 1/4, which fixes the issues seen so far, but it is a heuristic, and I expect that certain positions might require an even smaller fraction.
The patch was tested as a bug fix and passed:
STC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 56601 W: 12633 L: 12581 D: 31387
http://tests.stockfishchess.org/tests/view/5d02b37a0ebc5925cf09f6da
LTC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 52042 W: 8907 L: 8837 D: 34298
http://tests.stockfishchess.org/tests/view/5d0319420ebc5925cf09fe57
Furthermore, to confirm that the shuffle extension in this form indeed still brings Elo, one more test at VLTC was performed:
VLTC:
LLR: 2.96 (-2.94,2.94) [0.00,3.50]
Total: 142022 W: 20963 L: 20435 D: 100624
http://tests.stockfishchess.org/tests/view/5d03630d0ebc5925cf0a011a
Bench: 3961247
Since root_probe() and root_probe_wdl() do not reset all tbRank values if they fail,
it is necessary to do this in rank_root_move(). This fixes issue #2196.
Alternatively, the loop could be moved into both root_probe() and root_probe_wdl().
No functional change
This is a non-functional simplification.
backmost_sq and frontmost_sq are redundant. It seems quite clear to always use frontmost_sq and use the correct color.
Non functional change.
Increase size of the pawns table by the factor 8. This decreases the number of recalculations of pawn structure information significantly (at least at LTC).
I have done measurements for different depths and pawn cache sizes.
First are given the number of pawn entry calculations are done (in parentheses is the frequency that a call to probe triggers a pawn entry calculation). The delta% are the percentage of less done pawn entry calculations in comparison to master
VSTC: bench 1 1 12
STC: bench 8 1 16
LTC: bench 64 1 20
VLTC: bench 512 1 24
VSTC STC LTC VLTC
master 82218(6%) 548935(6%) 2415422(7%) 9548071(7%)
pawncache*2 79859(6%) 492943(5%) 2084794(6%) 8275206(6%)
pawncache*4 78551(6%) 458758(5%) 1827770(5%) 7112531(5%)
pawncache*8 77963(6%) 439421(4%) 1649169(5%) 6128652(4%)
delta%(p2-m) -2.9% -10.2% -13.7% -13.3%
delta%(p4-m) -4.5% -16.4% -24.3% -25.5%
delta%(p8-m) -5.2% -20.0% -31.7% -35.8%
STC: (non-regression test because at STC the effect is smaller than at LTC)
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 22767 W: 5160 L: 5040 D: 12567
http://tests.stockfishchess.org/tests/view/5d00f6040ebc5925cf09c3e2
LTC:
LLR: 2.94 (-2.94,2.94) [0.00,4.00]
Total: 26340 W: 4524 L: 4286 D: 17530
http://tests.stockfishchess.org/tests/view/5d00a3810ebc5925cf09ba16
No functional change.
This is a functional simplification. This is NOT the exact version that was tested. Beyond the testing, an assignment was removed and a piece changes for consistency.
Instead of rewarding ANY square past an opponent pawn as an "outpost," only use squares that are protected by our pawn. I believe this is more consistent with what the chess world calls an "outpost."
STC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 23540 W: 5387 L: 5269 D: 12884
http://tests.stockfishchess.org/tests/view/5cf51e6d0ebc5925cf08b823
LTC
LLR: 2.94 (-2.94,2.94) [-3.00,1.00]
Total: 53085 W: 9271 L: 9204 D: 34610
http://tests.stockfishchess.org/tests/view/5cf5279e0ebc5925cf08b992
bench 3424592
Stockfish evaluates passed pawns in part based on a variable k, which shapes the passed pawn bonus based on the number of squares between the current square and promotion square that are attacked by enemy pieces, and the number defended by friendly ones. Prior to this commit, we gave a large bonus when all squares between the pawn and the promotion square were defended, and if they were not, a somewhat smaller bonus if at least the pawn's next square was. However, this distinction does not appear to provide any Elo at STC or LTC.
Where do we go from here? Many promising Elo-gaining patches were attempted in the past few months to refine passed pawn calculation, by altering the definitions of unsafe and defended squares. Stockfish uses these definitions to choose the value of k, so those tests interact with this PR. Therefore, it may be worthwhile to retest previously promising but not-quite-passing tests in the vicinity of this patch.
STC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 42344 W: 9455 L: 9374 D: 23515
http://tests.stockfishchess.org/tests/view/5cf83ede0ebc5925cf0904fb
LTC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 69548 W: 11855 L: 11813 D: 45880
http://tests.stockfishchess.org/tests/view/5cf8698f0ebc5925cf0908c8
Bench: 3854907
This is a non-functional simplification. Since our file_bb handles either Files or Squares, using Square here removes some code. Not likely any performance difference despite the test.
STC
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 6081 W: 1444 L: 1291 D: 3346
http://tests.stockfishchess.org/tests/view/5ceb3e2e0ebc5925cf07ab03
Non functional change.
We evaluate defended and unsafe squares for a passed pawn push based on friendly and enemy rooks and queens on the passed pawn's file. Prior to this patch, we further required that these rooks and queens be able to directly attack the passed pawn. However, this restriction appears unnecessary and worth almost exactly 0 Elo at LTC.
The simplified code allows rooks and queens to attack/defend the passed pawn through other pieces of either color.
STC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 29019 W: 6488 L: 6381 D: 16150
http://tests.stockfishchess.org/tests/view/5cdcf7270ebc5925cf05d30c
LTC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 54224 W: 9200 L: 9133 D: 35891
http://tests.stockfishchess.org/tests/view/5cddc6210ebc5925cf05eca3
Bench: 3415326
This is a non-functional simplification that combines vote counting and thread selecting in the same loop.
It is possible that the best thread would be updated more frequently than master, but I'm not sure it matters here. Perhaps "mostVotes" is a better name than "bestVote?"
STC (stopped early).
LLR: 0.70 (-2.94,2.94) [-3.00,1.00]
Total: 10714 W: 2329 L: 2311 D: 6074
http://tests.stockfishchess.org/tests/view/5ccc71470ebc5925cf03d244
No functional change.
