QueryPerformanceCounter problem and questions

[lordzero]

Hello

I'm trying change GetTickCount from my codes to QueryPerformanceCounter

code:

type TCustomTimer = class
  private
    PerfFrequency: Int64;
    InvPerfFrequency: Single;
  public
    function gettime: Single;
    constructor Create;
  end;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Edit1: TEdit;
    Memo1: TMemo;
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }

    procedure Teste(Sender: TObject; var Done: Boolean);
  end;

var
  Form1: TForm1;
  clock: TCustomTimer;
  _start, _end: Double;


implementation

{$R *.dfm}
///////////////
{ TCustomTimer }

procedure TForm1.Teste(Sender: TObject; var Done: Boolean);
begin

   _end := clock.gettime;



   //1000 = frequencia de intervalo em milesegundos


   if (_end-_start) >= 1000 then
   begin

     memo1.Lines.Add('evento');
     _start := _end;


   end;

end;

constructor TCustomTimer.Create;
begin
  QueryPerformanceFrequency(PerfFrequency);
  InvPerfFrequency := 1.0 / PerfFrequency;
end;

function TCustomTimer.gettime: Single;
var
  Time: Int64;
begin
  QueryPerformanceCounter(Time);
  Result := 1000 * InvPerfFrequency * Time;
end;
///////////////

procedure TForm1.FormCreate(Sender: TObject);
begin


  clock := TCustomTimer.Create;

  
  _start := clock.gettime;

  application.OnIdle := Form1.Teste;


end;

procedure TForm1.FormDestroy(Sender: TObject);
begin

  Clock.Free;

end;

my code is ok?


my question...

what is this line?

 InvPerfFrequency := 1.0 / PerfFrequency;

[waran]

You don't know what your own code does :?:
I guess you are calculating the inverse of the frequency since
you don't have to divide (slow) each time you get your time,
but multiply instead.

Your code looks correct to me.
Maybe you should use double because single suffers from
rounding errors using such big numbers.

[lordzero]

You don't know what your own code does :?:
I guess you are calculating the inverse of the frequency since
you don't have to divide (slow) each time you get your time,
but multiply instead.

Your code looks correct to me.
Maybe you should use double because single suffers from
rounding errors using such big numbers.

I dont have created all of this code, and this is why i''m asking..

about queryperformancecounter sometimes this can fail in some hardware? and i need use a timer with low precision(GetTickCount)?

i know about this reading some webpage... actually this is not much clear...

[waran]

The PerformanceCounter works in Hardware if equipped (which is common nowadays).
If no PerformanceCounter is available QueryPerformanceFrequency will return 0 (false) - you have to use something else then.

[lordzero]

The PerformanceCounter works in Hardware if equipped (which is common nowadays).
If no PerformanceCounter is available QueryPerformanceFrequency will return 0 (false) - you have to use something else then.

gettickcount for example?

about queryperformancecounter what value it return? cpu cycles?

[waran]

The PerformanceCounter, unlike rdtsc, runs independent from your CPU
and the frequency can vary (simply called "ticks per second").
Its an independent hardware part on your mainboard.
Ticks divided with the frequency gives you seconds.

Yes, you can use GetTickCount instead since its purely software-based
(like SDL_GetTicks or Windows' Multimedia-Timer). But the PerfCounter
is usually the best choice if available.

[lordzero]

The PerformanceCounter, unlike rdtsc, runs independent from your CPU
and the frequency can vary (simply called "ticks per second").
Its an independent hardware part on your mainboard.
Ticks divided with the frequency gives you seconds.

Yes, you can use GetTickCount instead since its purely software-based
(like SDL_GetTicks or Windows' Multimedia-Timer). But the PerfCounter
is usually the best choice if available.

what style of hardware dont have this avaliable?

486 ?

[lordzero]

is ok now?

TCustomTimer = class
private
PerfFrequency: Int64;
InvPerfFrequency: Double;

function TCustomTimer.gettime: Double;
var
Time: Int64;
begin
QueryPerformanceCounter(Time);
Result := 1000 * InvPerfFrequency * Time;
end;

[lordzero]

some comments about this optimized counter?

http://17slon.com/blogs/gabr/labels/open%20source.html

look the function:

function GetTickCount64_Acc: int64;

[arthurprs]

is ok now?

TCustomTimer = class
private
PerfFrequency: Int64;
InvPerfFrequency: Double;

function TCustomTimer.gettime: Double;
var
Time: Int64;
begin
QueryPerformanceCounter(Time);
Result := 1000 * InvPerfFrequency * Time;
end;

the gettime function desnot need to return a float type, since it always result in a plain natural number