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Fix tablebase probe for dtz >1000 w/o 50 move rule

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For qn4N1/6R1/3K4/8/B2k4/8/8/8 w - - 0 1, white loses with DTZ 1034.
See https://syzygy-tables.info/?fen=qn4N1/6R1/3K4/8/B2k4/8/8/8_w_-_-_0_1

Prior to this fix, due to a too small hard-coded value, Stockfish interpreted this as winning.
The new value picked (1<<18) is large enough to deal with the largest DTZ values that can be stored in the current syzygy format.

closes https://github.com/official-stockfish/Stockfish/pull/4187

No functional change.
This commit is contained in:
Rodrigo Roim 2022-10-07 16:55:07 -07:00 • committed by Joost VandeVondele
parent 9be2977da7
commit 79c5f3a692
3 changed files with 8 additions and 8 deletions
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1
AUTHORS
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@ -169,6 +169,7 @@ renouve
Reuven Peleg
Richard Lloyd
Rodrigo Exterckötter Tjäder
Rodrigo Roim (roim)
Ron Britvich (Britvich)
Ronald de Man (syzygy1, syzygy)
rqs

13
src/syzygy/tbprobe.cpp
View file

@ -59,6 +59,7 @@ namespace Stockfish {
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.
enum { BigEndian, LittleEndian };
enum TBType { WDL, DTZ }; // Used as template parameter
@ -1522,7 +1523,7 @@ bool Tablebases::root_probe(Position& pos, Search::RootMoves& rootMoves) {
// Check whether a position was repeated since the last zeroing move.
bool rep = pos.has_repeated();
int dtz, bound = Options["Syzygy50MoveRule"] ? 900 : 1;
int dtz, bound = Options["Syzygy50MoveRule"] ? (MAX_DTZ - 100) : 1;
// Probe and rank each move
for (auto& m : rootMoves)
@ -1565,8 +1566,8 @@ bool Tablebases::root_probe(Position& pos, Search::RootMoves& rootMoves) {
// 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 ? 1000 : 1000 - (dtz + cnt50))
: dtz < 0 ? (-dtz * 2 + cnt50 < 100 ? -1000 : -1000 + (-dtz + cnt50))
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))
: 0;
m.tbRank = r;
@ -1574,9 +1575,9 @@ bool Tablebases::root_probe(Position& pos, Search::RootMoves& rootMoves) {
// 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 - 800) * int(PawnValueEg)) / 200)
: r > 0 ? Value((std::max( 3, r - (MAX_DTZ - 200)) * int(PawnValueEg)) / 200)
: r == 0 ? VALUE_DRAW
: r > -bound ? Value((std::min(-3, r + 800) * int(PawnValueEg)) / 200)
: r > -bound ? Value((std::min(-3, r + (MAX_DTZ - 200)) * int(PawnValueEg)) / 200)
: -VALUE_MATE + MAX_PLY + 1;
}
@ -1590,7 +1591,7 @@ bool Tablebases::root_probe(Position& pos, Search::RootMoves& rootMoves) {
// A return value false indicates that not all probes were successful.
bool Tablebases::root_probe_wdl(Position& pos, Search::RootMoves& rootMoves) {
static const int WDL_to_rank[] = { -1000, -899, 0, 899, 1000 };
static const int WDL_to_rank[] = { -MAX_DTZ, -MAX_DTZ + 101, 0, MAX_DTZ - 101, MAX_DTZ };
ProbeState result;
StateInfo st;

2
src/syzygy/tbprobe.h
View file

@ -31,8 +31,6 @@ enum WDLScore {
WDLDraw = 0, // Draw
WDLCursedWin = 1, // Win, but draw under 50-move rule
WDLWin = 2, // Win
WDLScoreNone = -1000
};
// Possible states after a probing operation