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Correct and extend PV lines with decisive TB score

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Currently (after #5407), SF has the property that any PV line with a decisive
TB score contains the corresponding TB position, with a score that correctly
identifies the depth at which TB are entered. The PV line that follows might
not preserve the game outcome, but can easily be verified and extended based on
TB information. This patch provides this functionality, simply extending the PV
lines on output, this doesn't affect search.

Indeed, if DTZ tables are available, search based PV lines that correspond to
decisive TB scores are verified to preserve game outcome, truncating the line
as needed. Subsequently, such PV lines are extended with a game outcome
preserving line until mate, as a possible continuation.  These lines are not
optimal mating lines, but are similar to what a user could produce on a website
like https://syzygy-tables.info/ clicking always the top ranked move, i.e.
minimizing or maximizing DTZ (with a simple tie-breaker for moves that have
identical DTZ), and are thus an just an illustration of how to game can be won.

A similar approach is already in established in
https://github.com/joergoster/Stockfish/tree/matefish2

This also contributes to addressing #5175 where SF can give an incorrect TB
win/loss for positions in TB with a movecounter that doesn't reflect optimal
play. While the full solution requires either TB generated differently, or a
search when ranking rootmoves, current SF will eventually find a draw in these
cases, in practice quite quickly, e.g.
`1kq5/q2r4/5K2/8/8/8/8/7Q w - - 96 1`
`8/8/6k1/3B4/3K4/4N3/8/8 w - - 54 106`

Gives the same results as master on an extended set of test positions from
https://github.com/mcostalba/Stockfish/commit/9173d29c414ddb8f4bec74e4db3ccbe664c66bf9
with the exception of the above mentioned fen where this commit improves.

With https://github.com/vondele/matetrack using 6men TB, all generated PVs verify:
```
Using ../Stockfish/src/stockfish.syzygyExtend on matetrack.epd with --nodes 1000000 --syzygyPath /chess/syzygy/3-4-5-6/WDL:/chess/syzygy/3-4-5-6/DTZ
Engine ID:     Stockfish dev-20240704-ff227954
Total FENs:    6555
Found mates:   3299
Best mates:    2582
Found TB wins: 568
```

As repeated DTZ probing could be slow a procedure (100ms+ on HDD, a few ms on
SSD), the extension is only done as long as the time taken is less than half
the `Move Overhead` parameter. For tournaments where these lines might be of
interest to the user, a suitable `Move Overhead` might be needed (e.g. TCEC has
1000ms already).

closes https://github.com/official-stockfish/Stockfish/pull/5414

No functional change
This commit is contained in:
Joost VandeVondele
2024-06-25 16:54:25 +02:00
parent 3c379e55d9
commit 2cbc20e846
4 changed files with 186 additions and 31 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/syzygy/tbprobe.cpp
+18 -11
View File
@@ -66,7 +66,7 @@ namespace {
constexpr int TBPIECES = 7; // Max number of supported pieces
constexpr int MAX_DTZ =
1 << 18; // Max DTZ supported, large enough to deal with the syzygy TB limit.
1 << 18; // Max DTZ supported times 2, large enough to deal with the syzygy TB limit.
enum {
BigEndian,
@@ -1574,7 +1574,10 @@ int Tablebases::probe_dtz(Position& pos, ProbeState* result) {
// Use the DTZ tables to rank root moves.
//
// A return value false indicates that not all probes were successful.
bool Tablebases::root_probe(Position& pos, Search::RootMoves& rootMoves, bool rule50) {
bool Tablebases::root_probe(Position& pos,
Search::RootMoves& rootMoves,
bool rule50,
bool rankDTZ) {
ProbeState result = OK;
StateInfo st;
@@ -1585,7 +1588,7 @@ bool Tablebases::root_probe(Position& pos, Search::RootMoves& rootMoves, bool ru
// Check whether a position was repeated since the last zeroing move.
bool rep = pos.has_repeated();
int dtz, bound = rule50 ? (MAX_DTZ - 100) : 1;
int dtz, bound = rule50 ? (MAX_DTZ / 2 - 100) : 1;
// Probe and rank each move
for (auto& m : rootMoves)
@@ -1624,8 +1627,10 @@ bool Tablebases::root_probe(Position& pos, Search::RootMoves& rootMoves, bool ru
// Better moves are ranked higher. Certain wins are ranked equally.
// Losing moves are ranked equally unless a 50-move draw is in sight.
int r = dtz > 0 ? (dtz + cnt50 <= 99 && !rep ? MAX_DTZ : MAX_DTZ - (dtz + cnt50))
: dtz < 0 ? (-dtz * 2 + cnt50 < 100 ? -MAX_DTZ : -MAX_DTZ + (-dtz + cnt50))
int r = dtz > 0 ? (dtz + cnt50 <= 99 && !rep ? MAX_DTZ - (rankDTZ ? dtz : 0)
: MAX_DTZ / 2 - (dtz + cnt50))
: dtz < 0 ? (-dtz * 2 + cnt50 < 100 ? -MAX_DTZ - (rankDTZ ? dtz : 0)
: -MAX_DTZ / 2 + (-dtz + cnt50))
: 0;
m.tbRank = r;
@@ -1633,10 +1638,11 @@ bool Tablebases::root_probe(Position& pos, Search::RootMoves& rootMoves, bool ru
// 1 cp to cursed wins and let it grow to 49 cp as the positions gets
// closer to a real win.
m.tbScore = r >= bound ? VALUE_MATE - MAX_PLY - 1
: r > 0 ? Value((std::max(3, r - (MAX_DTZ - 200)) * int(PawnValue)) / 200)
: r == 0 ? VALUE_DRAW
: r > -bound ? Value((std::min(-3, r + (MAX_DTZ - 200)) * int(PawnValue)) / 200)
: -VALUE_MATE + MAX_PLY + 1;
: r > 0 ? Value((std::max(3, r - (MAX_DTZ / 2 - 200)) * int(PawnValue)) / 200)
: r == 0 ? VALUE_DRAW
: r > -bound
? Value((std::min(-3, r + (MAX_DTZ / 2 - 200)) * int(PawnValue)) / 200)
: -VALUE_MATE + MAX_PLY + 1;
}
return true;
@@ -1683,7 +1689,8 @@ bool Tablebases::root_probe_wdl(Position& pos, Search::RootMoves& rootMoves, boo
Config Tablebases::rank_root_moves(const OptionsMap& options,
Position& pos,
Search::RootMoves& rootMoves) {
Search::RootMoves& rootMoves,
bool rankDTZ) {
Config config;
if (rootMoves.empty())
@@ -1707,7 +1714,7 @@ Config Tablebases::rank_root_moves(const OptionsMap& options,
if (config.cardinality >= popcount(pos.pieces()) && !pos.can_castle(ANY_CASTLING))
{
// Rank moves using DTZ tables
config.rootInTB = root_probe(pos, rootMoves, options["Syzygy50MoveRule"]);
config.rootInTB = root_probe(pos, rootMoves, options["Syzygy50MoveRule"], rankDTZ);
if (!config.rootInTB)
{
src/syzygy/tbprobe.h
+5 -2
View File
@@ -66,9 +66,12 @@ extern int MaxCardinality;
void init(const std::string& paths);
WDLScore probe_wdl(Position& pos, ProbeState* result);
int probe_dtz(Position& pos, ProbeState* result);
bool root_probe(Position& pos, Search::RootMoves& rootMoves, bool rule50);
bool root_probe(Position& pos, Search::RootMoves& rootMoves, bool rule50, bool rankDTZ);
bool root_probe_wdl(Position& pos, Search::RootMoves& rootMoves, bool rule50);
Config rank_root_moves(const OptionsMap& options, Position& pos, Search::RootMoves& rootMoves);
Config rank_root_moves(const OptionsMap& options,
Position& pos,
Search::RootMoves& rootMoves,
bool rankDTZ = false);
} // namespace Stockfish::Tablebases