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Fix go mate x in multithreading

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Fixes two issues with master for go mate x:

- when running go mate x in losing positions, master always goes to the
  maximal depth, arguably against what the UCI protocol demands

- when running go mate x in winning positions with multiple
  threads, master may return non-mate scores from the search (this issue
  is present in stockfish since at least sf16) The issues are fixed by
  (a) also checking if score is mate -x and by (b) only letting
  mainthread stop the search for go mate x commands, and by not looking
  for a best thread but using mainthread as per the default. Related:
    niklasf/python-chess#1070

More diagnostics can be found here peregrineshahin#6 (comment)

closes https://github.com/official-stockfish/Stockfish/pull/5094

No functional change

Co-Authored-By: Robert Nürnberg <28635489+robertnurnberg@users.noreply.github.com>
This commit is contained in:
Shahin M. Shahin 2024-03-06 20:56:55 +03:00 • committed by Disservin
parent 6136d094c5
commit 748791f80d
1 changed files with 10 additions and 6 deletions
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16
src/search.cpp
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@ -187,7 +187,7 @@ void Search::Worker::start_searching() {
Skill skill = Skill skill =
Skill(options["Skill Level"], options["UCI_LimitStrength"] ? int(options["UCI_Elo"]) : 0); Skill(options["Skill Level"], options["UCI_LimitStrength"] ? int(options["UCI_Elo"]) : 0);
if (int(options["MultiPV"]) == 1 && !limits.depth && !skill.enabled() if (int(options["MultiPV"]) == 1 && !limits.depth && !limits.mate && !skill.enabled()
&& rootMoves[0].pv[0] != Move::none()) && rootMoves[0].pv[0] != Move::none())
bestThread = threads.get_best_thread()->worker.get(); bestThread = threads.get_best_thread()->worker.get();
@ -399,14 +399,18 @@ void Search::Worker::iterative_deepening() {
lastBestMoveDepth = rootDepth; lastBestMoveDepth = rootDepth;
} }
// Have we found a "mate in x"?
if (limits.mate && bestValue >= VALUE_MATE_IN_MAX_PLY
&& VALUE_MATE - bestValue <= 2 * limits.mate)
threads.stop = true;
if (!mainThread) if (!mainThread)
continue; continue;
// Have we found a "mate in x"?
if (limits.mate && rootMoves[0].score == rootMoves[0].uciScore
&& ((rootMoves[0].score >= VALUE_MATE_IN_MAX_PLY
&& VALUE_MATE - rootMoves[0].score <= 2 * limits.mate)
|| (rootMoves[0].score != -VALUE_INFINITE
&& rootMoves[0].score <= VALUE_TB_LOSS_IN_MAX_PLY
&& VALUE_MATE + rootMoves[0].score <= 2 * limits.mate)))
threads.stop = true;
// If the skill level is enabled and time is up, pick a sub-optimal best move // If the skill level is enabled and time is up, pick a sub-optimal best move
if (skill.enabled() && skill.time_to_pick(rootDepth)) if (skill.enabled() && skill.time_to_pick(rootDepth))
skill.pick_best(rootMoves, multiPV); skill.pick_best(rootMoves, multiPV);