- // We use Position::set() to set root position across threads. So we
- // need to save and later to restore st->previous, cleared by set().
- // Note that setupStates is shared by threads but is accessed in read-only mode.
- StateInfo* previous = setupStates->back().previous;
+ // We use Position::set() to set root position across threads. But there are
+ // some StateInfo fields (previous, pliesFromNull, capturedPiece) that cannot
+ // be deduced from a fen string, so set() clears them and to not lose the info
+ // we need to backup and later restore setupStates->back(). Note that setupStates
+ // is shared by threads but is accessed in read-only mode.
+ StateInfo tmp = setupStates->back();