Trunc vs Round(x - 4.9999999999) :) Speeding up my app.

[erikphilips]

Alright so i read that trunc is "slow" so I did some testing. Interestingly enough it is.

procedure TForm1.Button1Click(Sender: TObject);
var
  endTick: integer;
  count: integer;
  i: integer;
  j: real;
begin
  edit1.Text := 'started';
  j := 2.4;
  endTick := GetTickCount + 5000;
  count := 0;
  repeat
    i := trunc(j);
    count := count + 1;
  until (getTickCount > endTick);
  edit1.Text := intToStr(count);
end;

There is a little about a 3% +/- change each time i ran it. Anway:
RoundL = a function using the round below
RoundO = a created object with a function using the round below

Trunc = 183,419,960 / ~5000 = 36,683/ms
Round(j - 4.9999999999) = 266,647,840 / ~5000 = 53,329/ms
RoundL = 157,383,577 / ~5000 = 31,376/ms
RoundO = 168202037 / ~5000 = 33,640/ms

So basically to get speed i have to manually type the round function in each spot i need to use it. It sounds crazy but it seems to be the only solution i've found.

[Clootie]

You are using wrong benchmarking technology - by calling getTickCount every loop, so it has big influence on final results.
Something like:
[pascal]for k:= 0 to 100 do
i:= i + trunc(j+k);
[/pascal]
instead of:
i := trunc(j);

[siim]

To get really accurate test results you should do something like this:

function QueryPerformanceCounter(lpPerformanceCount: PComp): Boolean; stdcall; external 'KERNEL32.DLL';
function QueryPerformanceFrequency(lpFrequency: PComp): Boolean; stdcall; external 'KERNEL32.DLL';

procedure TForm1.Button1Click(Sender: TObject);
var
  perfFreq: Comp;
  startTime, endTime: Comp;
  microSeconds: Longword;
  I: Integer;
  X: Single;
begin
  QueryPerformanceFrequency(@perfFreq);
  QueryPerformanceCounter(@startTime);
  X := 5.5;
  for I := 1 to 1000 do
  begin
    X := Round(X); X := Round(X); X := Round(X); X := Round(X);
  end;
  QueryPerformanceCounter(@endTime);
  microSeconds := Round((endTime - startTime)*1000000/perfFreq);
  ShowMessage(IntToStr(microSeconds)+' mics.');
end;

With trunc i got 210 microseconds and with round i got 155 microseconds.

Siim

[siim]

one microsecond = one second / one million
I have 1 Ghz duron and those timing functions take something between
1 and 2 microseconds and the loop itself takes 2 microseconds.
So one Round() = 30 nanoseconds = 30 hz
one Trunc() = 42 nanoseconds = 42 hz

Siim

[Clootie]

Additional note: different versions of Delphi have different implementation of Round and Trunc functions :shock: :twisted:

[erikphilips]

one microsecond = one second / one million
I have 1 Ghz duron and those timing functions take something between
1 and 2 microseconds and the loop itself takes 2 microseconds.
So one Round() = 30 nanoseconds = 30 hz
one Trunc() = 42 nanoseconds = 42 hz

Siim

Yup, but if I were to use Alimonsters gamma ramp control http://terraqueous.f2o.org/dgdev/viewtopic.php?t=17 I would be doing:
765 Round()'s = 22,950 nanoseconds
765 Trunc()'s = 32,130 nanoseconds

Now it starts adding up, I just want almost the best performance. Swapping Trunc with Round(x - 4.999999999) seems viable, i may lose some precision (not worried), but i'm not doing ASM. So even though the amount of time for one call isn't concern, calling them hundreds of time can reduce a projects performance.