Implement a threefold repetition detection. Below are the examples of
problems fixed by this change.
Loosing move in a drawn position.
position fen 8/k7/3p4/p2P1p2/P2P1P2/8/8/K7 w - - 0 1 moves a1a2 a7a8 a2a1
The old code suggested a loosing move "bestmove a8a7", the new code suggests "bestmove a8b7" leading to a draw.
Incorrect evaluation (happened in a real game in TCEC Season 9).
position fen 4rbkr/1q3pp1/b3pn2/7p/1pN5/1P1BBP1P/P1R2QP1/3R2K1 w - - 5 31 moves e3d4 h8h6 d4e3
The old code evaluated it as "cp 0", the new code evaluation is around "cp -50" which is adequate.
Brings 0.5-1 ELO gain. Passes [-3.00,1.00].
STC: http://tests.stockfishchess.org/tests/view/584ece040ebc5903140c5aea
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 47744 W: 8537 L: 8461 D: 30746
LTC: http://tests.stockfishchess.org/tests/view/584f134d0ebc5903140c5b37
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 36775 W: 4739 L: 4639 D: 27397
Patch has been rewritten into current form for simplification and
logic slightly changed so that return a draw score if the position
repeats once earlier but after or at the root, or repeats twice
strictly before the root. In its original form, repetition at root
was not returned as an immediate draw.
After retestimng testing both version with SPRT[-3, 1], both passed
succesfully, but this version was chosen becuase more natural. There is
an argument about MultiPV in which an extended draw at root may be sensible.
See discussion here:
https://github.com/official-stockfish/Stockfish/pull/925
For documentation, current version passed both at STC and LTC:
STC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 51562 W: 9314 L: 9245 D: 33003
LTC
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 115663 W: 14904 L: 14906 D: 85853
bench: 5468995
This patch fixed bugs #859 and #882.
At initialization we generate a new random key (Zobrist::noPawns).
It's added to the pawn key of all positions, so that the pawn key
of a pawnless position is no longer 0.
STC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 21307 W: 3738 L: 3618 D: 13951
LTC:
LLR: 2.94 (-2.94,2.94) [-3.00,1.00]
Total: 45270 W: 5737 L: 5648 D: 33885
No functional change.
A position can never repeat the one on the previous move.
Thus we can start searching for a repetition from the 4th
ply behind. In the case:
std::min(st->rule50, st->pliesFromNull) < 4
We don't need to do any more calculations. This case happens
very often - in more than a half of all calls of the function.
No functional change.
Currently, we only check if there is a pawn in place
to make the en-passant capture. Now also check that
there is a pawn that could just have advanced two
squares. Also update the corresponding comment.
This makes the parsing of FENs a bit more robust, and
now correctly handles positions like the one reported by Dann Corbit.
position fen rnbqkb1r/ppp3pp/3p1n2/3P4/8/2P5/PP3PPP/RNBQKB1R w KQkq e6
d
+---+---+---+---+---+---+---+---+
| r | n | b | q | k | b | | r |
+---+---+---+---+---+---+---+---+
| p | p | p | | | | p | p |
+---+---+---+---+---+---+---+---+
| | | | p | | n | | |
+---+---+---+---+---+---+---+---+
| | | | P | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | P | | | | | |
+---+---+---+---+---+---+---+---+
| P | P | | | | P | P | P |
+---+---+---+---+---+---+---+---+
| R | N | B | Q | K | B | | R |
+---+---+---+---+---+---+---+---+
Fen: rnbqkb1r/ppp3pp/3p1n2/3P4/8/2P5/PP3PPP/RNBQKB1R w KQkq - 0 1
No functional change.
Rewrite the code in SF style, simplify and
document it.
Code is now much clear and bug free (no mem-leaks and
other small issues) and is also smaller (more than
600 lines of code removed).
All the code has been rewritten but root_probe() and
root_probe_wdl() that are completely misplaced and should
be retired altogheter. For now just leave them in the
original version.
Code is fully and deeply tested for equivalency both in
functionality and in speed with hundreds of games and
test positions and is guaranteed to be 100% equivalent
to the original.
Tested with tb_dbg branch for functional equivalency on
more than 12M positions.
stockfish.exe bench 128 1 16 syzygy.epd
Position: 2016/2016
Total 12121156 Hits 0 hit rate (%) 0
Total time (ms) : 4417851
Nodes searched : 1100151204
Nodes/second : 249024
Tested with 5,000 games match against master, 1 Thread,
128 MB Hash each, tc 40+0.4, which is almost equivalent
to LTC in Fishtest on this machine. 3-, 4- and 5-men syzygy
bases on SSD, 12-moves opening book to emphasize mid- and endgame.
Score of SF-SyzygyC++ vs SF-Master: 633 - 617 - 3750 [0.502] 5000
ELO difference: 1
No functional change.
Stephane's patch removes the only usage of Position::see, where the
returned value isn't immediately compared with a value. So I replaced
this function by its optimised and more specific version see_ge. This
function also supersedes the function Position::see_sign.
bool Position::see_ge(Move m, Value v) const;
This function tests if the SEE of a move is greater or equal than a
given value. We use forward iteration on captures instread of backward
one, therefore we don't need the swapList array. Also we stop as soon
as we have enough information to obtain the result, avoiding unnecessary
calls to the min_attacker function.
Speed tests (Windows 7), 20 runs for each engine:
Test engine: mean 866648, st. dev. 5964
Base engine: mean 846751, st. dev. 22846
Speedup: 1.023
Speed test by Stephane Nicolet
Fishtest STC test:
LLR: 2.96 (-2.94,2.94) [0.00,5.00]
Total: 26040 W: 4675 L: 4442 D: 16923
http://tests.stockfishchess.org/tests/view/57f648990ebc59038170fa03
No functional change.
Use the following transformations:
- to check that A is included in B, testing "(A & ~B) == 0" is faster
than "(A & B) == A"
- to remove the intersection of A and B from A, doing "A &= ~B;" is as
fast as "if (A & B) A &= ~B;" but is simpler.
Overall, the simpler patch version is 0.3% than current master.
No functional change.
Correct pinners calculation and fix bug with pinned
pieces giving check. With this patch 'pinners' only
returns sliders with exactly one defensive piece between
the slider and the attacked square (in other words, pinners
returns exact pinners).
This was a co-operation between Marco Costalba,
Stphane Nicolet and me.
Special thanks to Ronald de Man for reporting the bug with
pinned pieces giving check, discussed here:
https://groups.google.com/forum/?fromgroups=#!topic/fishcooking/S_4E_Xs5HaE
STC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 132118 W: 23578 L: 23645 D: 84895
LTC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 36424 W: 4770 L: 4670 D: 26984
bench: 6272231
This is the most compact and neatest version
is was able to produce.
On normal builds I have a small slowdown:
normal builds base vs. simplification (gcc 4.8.1 Win7-64 i7-3770 @ 3.4GHz x86-64-modern)
Results for 20 tests for each version:
Base Test Diff
Mean 1974744 1969333 5411
StDev 11825 10281 5874
p-value: 0,178
speedup: -0,003
On pgo-builds however I measure a nice 1.1% speedup
pgo-builds base vs. simplification
Results for 20 tests for each version:
Base Test Diff
Mean 1974119 1995444 -21325
StDev 8703 5717 4623
p-value: 1
speedup: 0,011
No functional change.
Don't allow pinned pieces to attack the exchange-square as long all
pinners (this includes also potential ones) are on their original
square.
As soon a pinner moves to the exchange-square or get captured on it, we
fall back to standard SEE behaviour.
This correctly handles the majority of cases with absolute pins.
bench: 6883133
This greately simplifies usage because hides to the
search the implementation specific CheckInfo.
This is based on the work done by Marco in pull request #716,
implementing on top of it the ideas in the discussion: caching
the calls to slider_blockers() in the CheckInfo structure,
and simplifying the slider_blockers() function by removing its
first parameter.
Compared to master, bench is identical but the number of calls
to slider_blockers() during bench goes down from 22461515 to 18853422,
hopefully being a little bit faster overall.
archlinux, gcc-6
make profile-build ARCH=x86-64-bmi2
50 runs each
bench:
base = 2356320 +/- 981
test = 2403811 +/- 981
diff = 47490 +/- 1828
speedup = 0.0202
P(speedup > 0) = 1.0000
perft 6:
base = 175498484 +/- 429925
test = 183997959 +/- 429925
diff = 8499474 +/- 469401
speedup = 0.0484
P(speedup > 0) = 1.0000
perft 7 (but only 10 runs):
base = 185403228 +/- 468705
test = 188777591 +/- 468705
diff = 3374363 +/- 476687
speedup = 0.0182
P(speedup > 0) = 1.0000
$ ./pyshbench ../Stockfish/master ../Stockfish/test 20
run base test diff
...
base = 2501728 +/- 182034
test = 2532997 +/- 182034
diff = 31268 +/- 5116
speedup = 0.0125
P(speedup > 0) = 1.0000
No functional change.
Seems to give around 1% speed-up for CPUs with popcnt support.
Seems to give a very minor speed-up for CPUs without popcnt.
No functional change
Resolves#646
And passed in do_move(), this ensures maximum efficiency and
speed and at the same time unlimited move numbers.
The draw back is that to handle Position init we need to
reserve a StateInfo inside Position itself and use at
init time and when copying from another Position.
After lazy SMP we don't need anymore this gimmick and we can
get rid of this special case and always pass an external
StateInfo to Position object.
Also rewritten and simplified Position constructors.
Verified it does not regress with a 3 threads SMP test:
ELO: -0.00 +-12.7 (95%) LOS: 50.0%
Total: 1000 W: 173 L: 173 D: 654
No functional change.
Also a speedup(about 1%) on 64-bit w/o hardware popcnt
Retire Max15 and Full template parameters
(Contributed by Marco Costalba)
Now that we have just SW and HW versions, use
template default parameter to get rid of explicit
template parameters.
Retire bitcount.h and move the only defined
function to bitboard.h
No functional change
Resolves#620
Use Position::square and Position::squares instead.
This allow us to remove king_square(), simplify
endgames and to have more naming uniformity.
Moreover, this is a prerequisite step in case
in the future we decide to retire piece lists
altoghter and use pop_lsb() to loop across
pieces and serialize the moves. In this way
we just need to change definition of Position::square
to something like:
template<PieceType Pt> inline
Square Position::square(Color c) const {
return lsb(byColorBB[c]);
}
No functional change.
In Chess960 we can have legal positions with
opponent rook in A or H file and with castling
available, for instance:
4k3/pppppppp/8/8/8/8/PPPPPPPP/rR2K3 w Q - 0 1
In those cases we pick up the wrong rook when
setting castling.
Fix it by checking the color of the rook.
Bug reported by Matthew Lai.
No functional change.
Easier for tuning psq tables:
TUNE(myParameters, PSQT::init);
Also move PSQT code in a new *.cpp file, and retire the
old and hacky psqtab.h that required to be included only
once to work correctly, this is not idiomatic for a header
file.
Give wide visibility to psq tables (previously visible only
in position.cpp), this will easy the use of psq tables outside
Position, for instance in move ordering.
Finally trivial code style fixes of the latest patches.
Original patch of Lucas Braesch.
No functional change.
Currently Zobrist::castling[] are not properly zeroed
and rely on the compiler to do this at startup, but this
makes Position::init() to set different values every time
it is called!
This is a bit odd, and although not impacting normal usage,
can yield to subtle misbehaviour, very difficult to track
down, in case we happen to call it more than once for some
reason. I found this while developing tuning support and
it took me a while to track it down.
So properly init Zobrist::castling[]
No functional change.
Resolves#329
This micro-optimization only complicates the code and provides no benefit.
Removing it is even a speedup on my machine (i7-3770k, linux, gcc 4.9.1):
stat test master diff
mean 2,403,118 2,390,904 12,214
stdev 12,043 10,620 3,677
speedup 0.51%
P(speedup>0) 100.0%
No functional change.
Also remove useless StateCopySize64 optimization:
compiler uses SSE movups instruction anyhow and
does not need this trick (verified with fishbench).
No functional change.
Funny enough, gcc __builtin_prefetch() expects
already a void*, instead Windows's _mm_prefetch()
requires a char*.
The patch allows to remove ugly casts from caller
sites.
No functional change.
Results for 10 tests for each version (gcc 4.8.3 on mingw):
Base Test Diff
Mean 1502447 1507917 -5470
StDev 3119 1364 4153
p-value: 0,906
speedup: 0,004
Results for 10 tests for each version (MSVC 2013):
Base Test Diff
Mean 1400899 1403713 -2814
StDev 1273 2804 2700
p-value: 0,851
speedup: 0,002
No functional change.
It is up to material (and pawn) table look up
code to know where the per-thread tables are,
so change API to reflect this.
Also some comment fixing while there
No functional change.
