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Extra thinking before accepting draw PVs.

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If the PV leads to a draw (3-fold / 50-moves) position
and we're ahead of time, think a little longer, possibly
finding a better way.

As this is most likely effective at higher draw rates,
tried speculative LTC after a yellow STC:

STC:
http://tests.stockfishchess.org/tests/view/59eb173a0ebc590ccbb8975d
LLR: -2.95 (-2.94,2.94) [0.00,5.00]
Total: 56095 W: 10013 L: 9902 D: 36180
elo =    0.688 +-    1.711 LOS:   78.425%

LTC:
http://tests.stockfishchess.org/tests/view/59eba1670ebc590ccbb897b4
LLR: 2.95 (-2.94,2.94) [0.00,5.00]
Total: 59579 W: 7577 L: 7273 D: 44729
elo =    1.773 +-    1.391 LOS:   99.381%

bench: 5234652
This commit is contained in:
Joost VandeVondele 2017-10-20 19:17:49 +02:00 • committed by Marco Costalba
parent 287e2e2f74
commit e50af36a00
1 changed files with 27 additions and 2 deletions
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29
src/search.cpp
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@ -149,6 +149,7 @@ namespace {
void update_pv(Move* pv, Move move, Move* childPv);
void update_continuation_histories(Stack* ss, Piece pc, Square to, int bonus);
void update_stats(const Position& pos, Stack* ss, Move move, Move* quiets, int quietsCnt, int bonus);
bool pv_is_draw(Position& pos);
// perft() is our utility to verify move generation. All the leaf nodes up
// to the given depth are generated and counted, and the sum is returned.
@ -475,11 +476,17 @@ void Thread::search() {
// from the previous search and just did a fast verification.
const int F[] = { mainThread->failedLow,
bestValue - mainThread->previousScore };
int improvingFactor = std::max(229, std::min(715, 357 + 119 * F[0] - 6 * F[1]));
double unstablePvFactor = 1 + mainThread->bestMoveChanges;
Color us = rootPos.side_to_move();
bool thinkHard = DrawValue[us] == bestValue
&& Limits.time[us] - Time.elapsed() > Limits.time[~us]
&& ::pv_is_draw(rootPos);
double unstablePvFactor = 1 + mainThread->bestMoveChanges + thinkHard;
bool doEasyMove = rootMoves[0].pv[0] == easyMove
&& !thinkHard
&& mainThread->bestMoveChanges < 0.03
&& Time.elapsed() > Time.optimum() * 5 / 44;
@ -1427,6 +1434,24 @@ moves_loop: // When in check search starts from here
}
// Is the PV leading to a draw position? Assumes all pv moves are legal
bool pv_is_draw(Position& pos) {
StateInfo st[MAX_PLY];
auto& pv = pos.this_thread()->rootMoves[0].pv;
for (size_t i = 0; i < pv.size(); ++i)
pos.do_move(pv[i], st[i]);
bool isDraw = pos.is_draw(pv.size());
for (size_t i = pv.size(); i > 0; --i)
pos.undo_move(pv[i-1]);
return isDraw;
}
// When playing with strength handicap, choose best move among a set of RootMoves
// using a statistical rule dependent on 'level'. Idea by Heinz van Saanen.