编者澄清:最初发布时，有两个问题:

if (time - cb_last_orbital_update > 5000000)
{
    cb_last_orbital_update = time;
}

cb_last_orbital_update = time;

time - cb_last_orbital_update > 5000000

int main(void)
{
    ...
    double time = 0;
    double time_interval = 0.001;
    double cb_last_orbital_update = 0;

    F_Rocket_Preset(time, time_interval, ...);

    while(conditions)
    {
    Rocket[active].Stage[Rocket[active].r_stage].F_Update_Stage_Performance(time, time_interval, ...);
    Rocket[active].F_Calculate_Aerodynamic_Variables(time);
    Rocket[active].F_Calculate_Gravitational_Forces(cb_mu, cb_pos_d, time);
    Rocket[active].F_Update_Rotation(time, time_interval, ...);
    Rocket[active].F_Update_Position_Velocity(time_interval, time, ...);
    Rocket[active].F_Calculate_Orbital_Elements(cb_mu);
    F_Update_Celestial_Bodies(time, time_interval, ...);

    if (time - cb_last_orbital_update > 5000000.0)
    {
        cb_last_orbital_update = time;
    }

    Rocket[active].F_Check_Apoapsis(time, time_interval);
    Rocket[active].F_Status_Check(time, ...);
    Rocket[active].F_Update_Mass (time_interval, time);
    Rocket[active].F_Staging_Check (time, time_interval);

    time += time_interval;

    if (time > 3.1536E8)
    {
        std::cout << "\n\nBreak main loop! Sim Time: " << time << std::endl;
        break;
    }
    }
...
}

cb_last_orbital_update = time;

int cb_orbit_update_counter = 1; // before while loop

if(time - cb_orbit_update_counter * 5E6 > 0)
{
    cb_orbit_update_counter++;
}

__declspec(noinline) std::string F_Get_Body_Name(int r_body)
{
switch (r_body)
{
case 0:
    {
        return ("the Sun");
    }
case 1:
    {
        return ("Mercury");
    }
case 2:
    {
        return ("Venus");
    }
case 3:
    {
        return ("Earth");
    }
case 4:
    {
        return ("Mars");
    }
case 5:
    {
        return ("Jupiter");
    }
case 6:
    {
        return ("Saturn");
    }
case 7:
    {
        return ("Uranus");
    }
case 8:
    {
        return ("Neptune");
    }
case 9:
    {
        return ("Pluto");
    }
case 10:
    {
        return ("Ceres");
    }
case 11:
    {
        return ("the Moon");
    }
default:
    {
        return ("unnamed body");
    }
}

}

if(time - cb_orbit_update_counter * 1E7 > 0)
{
    F_Update_Orbital_Elements_Of_Celestial_Bodies(args);
    std::cout << F_Get_Body_Name(3) << " SMA: " << cb_sma[3] << "\tPos Earth: " << cb_pos_d[3][0] << " / " << cb_pos_d[3][1] << " / " << cb_pos_d[3][2] <<
    "\tAlt: " << sqrt(pow(cb_pos_d[3][0] - cb_pos_d[0][0],2) + pow(cb_pos_d[3][1] - cb_pos_d[0][1],2) + pow(cb_pos_d[3][2] - cb_pos_d[0][2],2)) << std::endl;
    std::cout << "Time: " << time << "\tcb_o_h[3]: " << cb_o_h[3] << std::endl;
    cb_orbit_update_counter++;
}

const std::string cb_names[] = {"the Sun","Mercury","Venus","Earth","Mars","Jupiter","Saturn","Uranus","Neptune","Pluto","Ceres","the Moon","unnamed body"}; // global definition
const int cb_number = 12; // global definition

std::string F_Get_Body_Name(int r_body)
{
if (r_body >= 0 && r_body < cb_number)
{
    return (cb_names[r_body]);
}
else
{
    return (cb_names[cb_number]);
}
}

最佳答案

我会把钱花在英特尔的分支预测器上。 http://en.wikipedia.org/wiki/Branch_predictor

处理器假设 (time - cb_last_orbital_update > 5000000) 大部分时间为假，并相应地加载执行管道。

一旦条件(时间 - cb_last_orbital_update > 5000000)成立。错误预测的延迟正在打击你。您可能会丢失 10 到 20 个周期。

if (time - cb_last_orbital_update > 5000000)
{
    cb_last_orbital_update = time;
}

关于c++ - 很少执行且几乎为空的 if 语句大大降低了 C++ 中的性能，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/29079984/