Currently we update (track up) the pv even in the fail high case.
However most times in such cases the pv in the ply below remains unset
because there we have value == alpha and so finally we see truncated
pv's (=just one move) in fail high cases.
Of course tracking down these pv's (+sending them to the gui) comes at a
certian cost, but no-regression tests passed:
STC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 16300 W: 3556 L: 3424 D: 9320
http://tests.stockfishchess.org/tests/view/5b9b73500ebc592cf275ea92
LTC:
LLR: 2.96 (-2.94,2.94) [-3.00,1.00]
Total: 202411 W: 32734 L: 32897 D: 136780
http://tests.stockfishchess.org/tests/view/5b9baed10ebc592cf275ef6d
N.B.: Digging also into qsearch was tried in another version but seemed
not to pass the tests. This means that we don't always will get a pv
until the very tips.
No functional change
The '- 1' subtrahend was introduced for guarding against null move
search at root, which would be nonsense. But this is actually already
guaranteed by the !PvNode condition. This followed from the discussion
in pull request 1609: https://github.com/official-stockfish/Stockfish/pull/1609
No functional change
1. avoid recursive call of verification.
For the interested side to move recursion makes no sense.
For the other side it could make sense in case of mutual zugzwang,
but I was not able to figure out any concrete problematic position.
Allows the removal of 2 local variables.
2. avoid further reduction by removing R += ONE_PLY;
Benchmark with zugzwang-suite (see #1338), max 45 secs per position:
Patch solves 33 out of 37
Master solves 31 out of 37
STC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 76188 W: 13866 L: 13840 D: 48482
http://tests.stockfishchess.org/tests/view/5a5612ed0ebc590297da516c
LTC:
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 40479 W: 5247 L: 5152 D: 30080
http://tests.stockfishchess.org/tests/view/5a56f7d30ebc590299e4550e
bench: 5340015
Results for 20 tests for each version (pgo-builds):
Base Test Diff
Mean 2110519 2118116 -7597
StDev 8727 4906 10112
p-value: 0,774
speedup: 0,004
Further verified for no regression:
http://tests.stockfishchess.org/tests/view/5885abd10ebc5915193f79e6
LLR: 2.95 (-2.94,2.94) [-3.00,1.00]
Total: 21786 W: 3959 L: 3840 D: 13987
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,
Stéphane 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
