Function StartupOneEngine

src/engine.cpp:717–792

* Start/initialise one engine. * @param e The engine to initialise. * @param aging_date The date used for age calculations. * @param seed Random seed. */

 * @param seed Random seed.
 */
void StartupOneEngine(Engine *e, const TimerGameCalendar::YearMonthDay &aging_ymd, uint32_t seed)
{
	const EngineInfo *ei = &e->info;

	e->age = 0;
	e->flags = {};
	e->company_avail = CompanyMask{};
	e->company_hidden = CompanyMask{};

	/* Vehicles with the same base_intro date shall be introduced at the same time.
	 * Make sure they use the same randomisation of the date. */
	SavedRandomSeeds saved_seeds;
	SaveRandomSeeds(&saved_seeds);
	SetRandomSeed(_settings_game.game_creation.generation_seed ^ seed ^
	              ei->base_intro.base() ^
	              e->type ^
	              e->GetGRFID());
	uint32_t r = Random();

	/* Don't randomise the start-date in the first two years after gamestart to ensure availability
	 * of engines in early starting games.
	 * Note: TTDP uses fixed 1922 */
	e->intro_date = ei->base_intro <= TimerGameCalendar::ConvertYMDToDate(_settings_game.game_creation.starting_year + 2, 0, 1) ? ei->base_intro : (TimerGameCalendar::Date)GB(r, 0, 9) + ei->base_intro;
	if (e->intro_date <= TimerGameCalendar::date) {
		TimerGameCalendar::YearMonthDay intro_ymd = TimerGameCalendar::ConvertDateToYMD(e->intro_date);
		int aging_months = aging_ymd.year.base() * 12 + aging_ymd.month;
		int intro_months = intro_ymd.year.base() * 12 + intro_ymd.month;
		if (intro_ymd.day > 1) intro_months++; // Engines are introduced at the first month start at/after intro date.
		e->age = aging_months - intro_months;
		e->company_avail.Set();
		e->flags.Set(EngineFlag::Available);
	}

	/* Get parent variant index for syncing reliability via random seed. */
	const Engine *re = e;
	while (re->info.variant_id != EngineID::Invalid() && re->info.extra_flags.Test(ExtraEngineFlag::SyncReliability)) {
		re = Engine::Get(re->info.variant_id);
	}

	SetRandomSeed(_settings_game.game_creation.generation_seed ^ seed ^
	              (re->index.base() << 16) ^ (re->info.base_intro.base() << 12) ^ (re->info.decay_speed << 8) ^
	              (re->info.lifelength.base() << 4) ^ re->info.retire_early ^
	              e->type ^
	              e->GetGRFID());

	/* Base reliability defined as a percentage of UINT16_MAX. */
	const uint16_t RELIABILITY_START = UINT16_MAX * 48 / 100;
	const uint16_t RELIABILITY_MAX   = UINT16_MAX * 75 / 100;
	const uint16_t RELIABILITY_FINAL = UINT16_MAX * 25 / 100;

	static_assert(RELIABILITY_START == 0x7AE0);
	static_assert(RELIABILITY_MAX   == 0xBFFF);
	static_assert(RELIABILITY_FINAL == 0x3FFF);

	r = Random();
	/* 14 bits gives a value between 0 and 16383, which is up to an additional 25%p reliability on top of the base reliability. */
	e->reliability_start = GB(r, 16, 14) + RELIABILITY_START;
	e->reliability_max   = GB(r,  0, 14) + RELIABILITY_MAX;