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Code Issues Releases Wiki Activity

Limit has_game_cycle() to only upcoming repetition

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use the original algorithm according to the paper
http://web.archive.org/web/20201107002606/https://marcelk.net/2013-04-06/paper/upcoming-rep-v2.pdf,
which detects accurately if a position has an upcoming repetition. The 'no
progress' part of has_game_cycle has been removed, the function has been
renamed to upcoming_repetition to reflect this.

As a result of this fix, to the best of our knowledge, all PVs for completed
iterations that yield a mate or decisive table base score now end in mate or
contain a TB position, respectively.

passed non-regression STC:
https://tests.stockfishchess.org/tests/view/6679fa1d0c2db3fa2dcecbf2
LLR: 2.96 (-2.94,2.94) <-1.75,0.25>
Total: 63584 W: 16666 L: 16472 D: 30446
Ptnml(0-2): 186, 7552, 16146, 7698, 210

Passed non-regression LTC:
https://tests.stockfishchess.org/tests/view/667ac965e439ed1c7a9ca042
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 464574 W: 117493 L: 117729 D: 229352
Ptnml(0-2): 311, 52468, 126974, 52214, 320

closes https://github.com/official-stockfish/Stockfish/pull/5432

bench: 1209805
This commit is contained in:
Shahin M. Shahin 2024-06-25 01:57:35 +03:00 • committed by Joost VandeVondele
parent 69ad4667fb
commit 6b7822119f
3 changed files with 15 additions and 17 deletions
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20
src/position.cpp
View file

@ -1156,9 +1156,9 @@ bool Position::has_repeated() const {
}
// Tests if the position has a move which draws by repetition,
// or an earlier position has a move that directly reaches the current position.
bool Position::has_game_cycle(int ply) const {
// Tests if the position has a move which draws by repetition.
// This function accurately matches the outcome of is_draw() over all legal moves.
bool Position::upcoming_repetition(int ply) const {
int j;
@ -1169,10 +1169,16 @@ bool Position::has_game_cycle(int ply) const {
Key originalKey = st->key;
StateInfo* stp = st->previous;
Key other = originalKey ^ stp->key ^ Zobrist::side;
for (int i = 3; i <= end; i += 2)
{
stp = stp->previous->previous;
stp = stp->previous;
other ^= stp->key ^ stp->previous->key ^ Zobrist::side;
stp = stp->previous;
if (other != 0)
continue;
Key moveKey = originalKey ^ stp->key;
if ((j = H1(moveKey), cuckoo[j] == moveKey) || (j = H2(moveKey), cuckoo[j] == moveKey))
@ -1188,12 +1194,6 @@ bool Position::has_game_cycle(int ply) const {
// For nodes before or at the root, check that the move is a
// repetition rather than a move to the current position.
// In the cuckoo table, both moves Rc1c5 and Rc5c1 are stored in
// the same location, so we have to select which square to check.
if (color_of(piece_on(empty(s1) ? s2 : s1)) != side_to_move())
continue;
// For repetitions before or at the root, require one more
if (stp->repetition)
return true;
}

2
src/position.h
View file

@ -156,7 +156,7 @@ class Position {
int game_ply() const;
bool is_chess960() const;
bool is_draw(int ply) const;
bool has_game_cycle(int ply) const;
bool upcoming_repetition(int ply) const;
bool has_repeated() const;
int rule50_count() const;
Value non_pawn_material(Color c) const;

10
src/search.cpp
View file

@ -534,9 +534,8 @@ Value Search::Worker::search(
// Limit the depth if extensions made it too large
depth = std::min(depth, MAX_PLY - 1);
// Check if we have an upcoming move that draws by repetition, or
// if the opponent had an alternative move earlier to this position.
if (!rootNode && alpha < VALUE_DRAW && pos.has_game_cycle(ss->ply))
// Check if we have an upcoming move that draws by repetition.
if (!rootNode && alpha < VALUE_DRAW && pos.upcoming_repetition(ss->ply))
{
alpha = value_draw(this->nodes);
if (alpha >= beta)
@ -1447,9 +1446,8 @@ Value Search::Worker::qsearch(Position& pos, Stack* ss, Value alpha, Value beta,
assert(PvNode || (alpha == beta - 1));
assert(depth <= 0);
// Check if we have an upcoming move that draws by repetition, or if
// the opponent had an alternative move earlier to this position. (~1 Elo)
if (alpha < VALUE_DRAW && pos.has_game_cycle(ss->ply))
// Check if we have an upcoming move that draws by repetition. (~1 Elo)
if (alpha < VALUE_DRAW && pos.upcoming_repetition(ss->ply))
{
alpha = value_draw(this->nodes);
if (alpha >= beta)