- Remove / add empty lines
- fix the `ttcapture` comment
- remove the `bonus` variable for `ttMoveHistory`
- remove unnecessary parentheses / brackets
- refactor the movepick good quiet stage
- rename `endMoves` to `endCur`, as the previous name suggests that it points to the end of all generated moves, which it does not.
closes https://github.com/official-stockfish/Stockfish/pull/6089
No functional change.
Co-Authored-By: xu-shawn <50402888+xu-shawn@users.noreply.github.com>
Change is functional because now we verify for stalemate also on captures and when not giving check.
Green STC test on stalemate-book
https://tests.stockfishchess.org/tests/view/682d878f6ec7634154f9ad2f
Elo: 2.29 ± 1.3 (95%) LOS: 100.0%
Total: 10000 W: 4637 L: 4571 D: 792
Ptnml(0-2): 2, 132, 4664, 202, 0
nElo: 12.42 ± 6.8 (95%) PairsRatio: 1.51
Green LTC test on stalemate-book
https://tests.stockfishchess.org/tests/view/682daa2d6ec7634154f9ad67
Elo: 0.80 ± 0.8 (95%) LOS: 96.9%
Total: 10000 W: 4727 L: 4704 D: 569
Ptnml(0-2): 0, 64, 4849, 87, 0
nElo: 6.51 ± 6.8 (95%) PairsRatio: 1.36
Passed non-regression test @ LTC
https://tests.stockfishchess.org/tests/view/682dd10d6ec7634154f9adb3
LLR: 2.95 (-2.94,2.94) <-1.75,0.25>
Total: 148512 W: 38135 L: 38046 D: 72331
Ptnml(0-2): 55, 15759, 42558, 15810, 74
N.B.: The unique concern I have, is that due changes in future a negative SEE
capture see might be returned in GOOD_CAPTURE stage. In this case the assert in
can_move_king_or_pawn() will trigger since we must guarantee that all moves
(also quiets) are generated in movepicker when calling can_move_king_or_pawn().
closes https://github.com/official-stockfish/Stockfish/pull/6088
bench: 2178135
Simplify the handling of good/bad quiets and make it more similar to the way we
handle good/bad captures. The good quiet limit was adjusted from -7998 to
-14000 to keep the ratio of good/bad quiets about the same as master. This
also fixes a "bug" that previously returned some bad quiets during the
GOOD_QUIET stage when some qood quiets weren't sorted at low depths.
STC https://tests.stockfishchess.org/tests/view/6827a68c6ec7634154f9992b
LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 75936 W: 19722 L: 19547 D: 36667
Ptnml(0-2): 186, 8937, 19589, 9028, 228
LTC https://tests.stockfishchess.org/tests/view/6828f8096ec7634154f99b82
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 104112 W: 26773 L: 26638 D: 50701
Ptnml(0-2): 51, 11363, 29098, 11488, 56
closes https://github.com/official-stockfish/Stockfish/pull/6071
Bench: 2007023
Currently SF’s quiescence search like most alpha-beta based engines
doesn’t verify for stalemate because doing it each leaf position is to
expensive and costs elo. However in certain positions this creates a
blindspot for SF, not recognizing soon enough that the opponent can
reach a stalemate by sacrifycing his last mobile heavy piece(s). This
tactical motif & it’s measure are similar to zugzwang & verification
search: the measure itself does not gain elo, but prevents SF from
loosing/drawing games in an awkward way.
The fix consists of 3 measures:
1. Make qsearch verify for stalemate on transitions to pure KP-material
for the side to move with our last Rook/Queen just been captured. In
fact this is the scenario where stalemate happens with highest
frequency. The stalemate-verification itself is optimized by merely
checking for pawn pushes & king mobility (captures were already
tried by qssearch)
2. Another culprit for the issue figured out to be SEE based pruning for
checks in step 14. Here often the move forcing the stalemate (or
forcing the opponent to not retake) get pruned away and it need to
much time to reach enough depth. To encounter this we verify
following conditions:
- a) side to move is happy with a draw (alpha < 0)
- b) we are about to sacrify our last heavy & unique mobile piece in
this position.
- c) this piece doesn’t move away from our kingring giving the king a
new square to move.
When all 3 conditions meet we don’t prune the move, because there
is a good chance that capturing the piece means stalemate.
3. Store terminal nodes (mates & stalemates) in TT with higher depth
than searched depth. This prevents SF from:
- reanalyzing the node (=trying to generate legal moves) in vain at
each iterative deepening step.
- overwriting an already correct draw-evaluation from a previous shallow
normal search by a qsearch which doesn’t recognize stalemate and might
store a verry erratic evaluation.
This is due to the 4 constant in the TT-overwrite condition: d -
DEPTH_ENTRY_OFFSET + 2 * pv > depth8 – 4 which allows qs to override
entries made by normal searches with depth <=4.
This 3hrd measure however is not essential for fixing the issue, but
tests (one of vdv & one of mine) seem to suggest that this measure
brings some small benefit.
Another other position where SF benefits from this fix is for instance
Position FEN 8/8/8/1B6/6p1/8/3K1Ppp/3N2kr w - - 0 1 bm f4 +M9
P.S.: Also this issue higly depends on the used net, how good the net is
at evaluate such mobility restricted positions. SF16 was pretty good in
solving 2rr4/5pBk/PqP3p1/1N3pPp/1PQ1bP1P/8/3R4/R4K2 b - - 0 40 bm Rxc6
(< 1 second) while SF16_1 with introduction of the dual net needs about
1,5 minutes and SF17.1 requires 3 minutes to find the drawing move Rxc6.
P.S.2: Using more threads produces indeterminism & using high hash
pressure makes SF reevaluate explored positions more often which makes
it more likely to solve the position. To have stable meaningful results
I tested therfore with one single thread and low hash pressure.
Preliminary LTC test at 30k games
https://tests.stockfishchess.org/tests/view/67ece7a931d7cf8afdc44e18 Elo: 0.04 ± 2.0 (95%) LOS: 51.7%
Total: 24416 W: 6226 L: 6223 D: 11967
Ptnml(0-2): 12, 2497, 7185, 2504, 10
nElo: 0.09 ± 4.4 (95%) PairsRatio: 1.00
Passed LTC no-regression sprt
https://tests.stockfishchess.org/tests/view/67ee8e4631d7cf8afdc452fb
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 401556 W: 101612 L: 101776 D: 198168
Ptnml(0-2): 152, 42241, 116170, 42049, 166
closes https://github.com/official-stockfish/Stockfish/pull/5983
fixes https://github.com/official-stockfish/Stockfish/issues/5899
Bench: 1721673
In the move generation the moves are generated in the order pawns, knight, bishops, rooks, queens and king.
This follows increasing type_of(pos.moved_piece(m)) term, so in master a capturing was sorted after a capturing rook if the same piece was captured in evasion.
Because we use a stable sorting method (stable means the order of elements with the same value are not changed) and generate the moves in the above order we do'nt need the removed term.
Passed STC:
LLR: 2.98 (-2.94,2.94) <-1.75,0.25>
Total: 170560 W: 44222 L: 44148 D: 82190
Ptnml(0-2): 569, 18792, 46488, 18858, 573
https://tests.stockfishchess.org/tests/view/678530ee460e2910c51de21d
closes https://github.com/official-stockfish/Stockfish/pull/5784
No functional change
* Limit use of `StatsEntry` wrapper to arithmetic types
* Generalize `Stats` to `MultiArray` by discarding the template parameter `D`
* Allow `MultiArray::fill` to take any type assignable to element type
* Remove now-unused operator overloads on `StatsEntry`
closes https://github.com/official-stockfish/Stockfish/pull/5750
No functional change
Since no correction histories are ever used inside Movepick, and many
existing histories are closely integrated into search, it might be more
logical to separate them into their own header. PR based on #5650
closes https://github.com/official-stockfish/Stockfish/pull/5652
No functional change
Idea of this patch comes from the fact that current history heuristics
are mostly populated by low depth entries since our stat bonus reaches
maximum value at depth 5-6 and number of low depth nodes is much bigger
than number of high depth nodes. But it doesn't make a whole lost of
sense to use this low-depth centered histories to sort moves at root.
Current patch introduces special history table that is used exclusively
at root, it remembers which quiet moves were good and which quiet moves
were not good there and uses this information for move ordering.
Passed STC:
https://tests.stockfishchess.org/tests/view/66dda74adc53972b68218cc9
LLR: 2.93 (-2.94,2.94) <0.00,2.00>
Total: 127680 W: 33579 L: 33126 D: 60975
Ptnml(0-2): 422, 15098, 32391, 15463, 466
Passed LTC:
https://tests.stockfishchess.org/tests/view/66dead2adc53972b68218d34
LLR: 2.95 (-2.94,2.94) <0.50,2.50>
Total: 381978 W: 96958 L: 95923 D: 189097
Ptnml(0-2): 277, 42165, 105089, 43162, 296
closes https://github.com/official-stockfish/Stockfish/pull/5595
Bench: 1611283
- Capitalize comments
- Reformat multi-lines comments to equalize the widths of the lines
- Try to keep the width of comments around 85 characters
- Remove periods at the end of single-line comments
closes https://github.com/official-stockfish/Stockfish/pull/5469
No functional change
Also "fix" movepicker to allow depths between CHECKS and NO_CHECKS,
which makes them easier to tweak (not that they get tweaked hardly ever)
(This was more beneficial when there was a third stage to DEPTH_QS, but
it's still an improvement now)
closes https://github.com/official-stockfish/Stockfish/pull/5205
No functional change
Parameters Tune, adding also another tunable parameter (npmDiv) to be
variable for different nets (bignet, smallnet, psqtOnly smallnet). P.s:
The changed values are only the parameters where there is agreement
among the different time controls, so in other words, the tunings are
telling us that changing these specific values to this specific
direction is good in all time controls, so there shouldn't be a high
risk of regressing at longer time controls.
Passed STC:
LLR: 2.97 (-2.94,2.94) <0.00,2.00>
Total: 39552 W: 10329 L: 9999 D: 19224
Ptnml(0-2): 156, 4592, 9989, 4844, 195
https://tests.stockfishchess.org/tests/view/661be9a0bd68065432a088c0
Passed LTC:
LLR: 2.94 (-2.94,2.94) <0.50,2.50>
Total: 56394 W: 14439 L: 14078 D: 27877
Ptnml(0-2): 30, 6152, 15480, 6497, 38
https://tests.stockfishchess.org/tests/view/661c746296961e72eb565406
closes https://github.com/official-stockfish/Stockfish/pull/5187
Bench: 1836777
Move divisor from capture scoring to good capture
check and sligthly increase it.
This has several effects:
- its a speedup because for quience and probcut
search the division now never happens. For main
search its delayed and can be avoided if a good
capture triggers a cutoff
- through the higher resolution of scores we have
a more granular sorting
STC: https://tests.stockfishchess.org/tests/view/65bf2a93c865510db027dc27
LLR: 2.93 (-2.94,2.94) <0.00,2.00>
Total: 470016 W: 122150 L: 121173 D: 226693
Ptnml(0-2): 2133, 55705, 118374, 56644, 2152
LTC: https://tests.stockfishchess.org/tests/view/65c1d16dc865510db0281339
LLR: 2.96 (-2.94,2.94) <0.50,2.50>
Total: 98988 W: 25121 L: 24667 D: 49200
Ptnml(0-2): 77, 10998, 26884, 11464, 71
closes https://github.com/official-stockfish/Stockfish/pull/5036
Bench: 1233867
