Changes

SearchStackEntry *past_stack = nullptr;if ((stack- 2)->improving_rate static_eval != kScoreNone) { past_stack = 0.0stack - 2;} else if ((stack - 4)->static_eval != kScoreNone) { past_stack = stack - 4;}

if (!state.InCheck() && !stack->excluded_tt_movepast_stack) { // Smoothen the improving rate from the static eval of our position in ...// previous turns const Score static_eval_diff diff = kScoreNone; double prev_improving_rate = 0.0; if ((stack - 2)->static_eval != kScoreNone) { static_eval_diff = stack->static_eval - (stack - 2)past_stack->static_eval; prev_improving_rate = (stack - 2)->improving_rate; } else if ((stack - 4)->static_eval != kScoreNone) { static_eval_diff = stack->static_eval - (stack - 4)->static_eval; prev_improving_rate = (stack - 4)->improving_rate; }  if (static_eval_diff != kScoreNone) { stack->improving_rate = prev_improving_rate + (static_eval_diff) / 25.0; stack->improving_rate = std::clamp(stackpast_stack->improving_rate+ diff / 50.0, 0.0, 1.0); }} else { stack->static_eval = eval = kScoreNone;