Compare two TIntegerDynArray

[shineworld 73]

Hi all,

 

what is the fastest way to compare two vars of the TIntegerDynArray type?
 

Thank you in advance for your suggestions.

 

 

[David Heffernan 2345]

First compare their length then do a CompareMem if the lengths are equal

[shineworld 73]

That is what I've used....

procedure TGCodeEditor.SetGCodeLinePoints(Value: TIntegerDynArray);
var
  F: Boolean;
  L: Integer;
begin
  F := False;
  L := Length(Value);
  if (Length(FGCodeLinePoints) > 0) and (Length(FGCodeLinePoints) = L) then
    F := CompareMem(@FGCodeLinePoints[0], @Value[0], Sizeof(Integer) * L);
  FGCodeLinePoints := Value;
  if not F then
    Invalidate;
end;

 

[David Heffernan 2345]

9 minutes ago, shineworld said:

That is what I've used....

procedure TGCodeEditor.SetGCodeLinePoints(Value: TIntegerDynArray);
var
  F: Boolean;
  L: Integer;
begin
  F := False;
  L := Length(Value);
  if (Length(FGCodeLinePoints) > 0) and (Length(FGCodeLinePoints) = L) then
    F := CompareMem(@FGCodeLinePoints[0], @Value[0], Sizeof(Integer) * L);
  FGCodeLinePoints := Value;
  if not F then
    Invalidate;
end;

 

Not much point having three calls to Length and in fact the zero length check can be skipped and rely on CompareMem to know what to do when passed a size of zero. 

[shineworld 73]

Some type like this? 

PS: IsEqualIntegerDynArray placed in method just to test.

procedure TGCodeEditor.SetGCodeLinePoints(Value: TIntegerDynArray);

  function IsEqualIntegerDynArray(const A, B: TIntegerDynArray): Boolean;
  begin
    if Length(A) <> Length(B) then Exit(False);
    Result := CompareMem(@A[0], @B[0], Sizeof(Integer) * Length(A));
  end;

begin
  if not IsEqualIntegerDynArray(FGCodeLinePoints, Value) then
  begin
    FGCodeLinePoints := Value;
    Invalidate;
  end;
end;

 

[David Heffernan 2345]

1 minute ago, shineworld said:

Result := CompareMem(@A[0], @B[0], Sizeof(Integer) * Length(A));

This risks range check errors so I'd use Pointer(A)^ and similar for B. You could still save one of the lengths to a local to avoid getting it twice. 

[David Heffernan 2345]

48 minutes ago, shineworld said:

TIntegerDynArray

Any reason why you aren't using TArray<Integer>?

[shineworld 73]

Sincerely no reason.
I just thought that TIntegerDynArray is more performant than a generic.

In my defense or fault, I have not been a big user of generics until now.

Edited November 22, 2022 by shineworld

[David Heffernan 2345]

10 minutes ago, shineworld said:

Sincerely no reason.
I just thought that TIntegerDynArray is more performant than a generic.

In my defense or fault, I have not been a big user of generics until now.

Don't think performance is an issue with TArray<T> and using it makes you code better able to work with other generic code. 

[Remy Lebeau 1394]

5 hours ago, shineworld said:

Some type like this? 

PS: IsEqualIntegerDynArray placed in method just to test.

If there is any possibility that FGCodeLinePoints could be passed in to SetGCodeLinePoints() (eg: GCodeEditor1.GCodeLinePoints := GCodeEditor1.GCodeLinePoints;), then I would also add a pointer equality check as well, since dynamic arrays are implemented as ref-counted pinters, eg:

procedure TGCodeEditor.SetGCodeLinePoints(Value: TIntegerDynArray);

  function IsEqualIntegerDynArray(const A, B: TIntegerDynArray): Boolean;
  var
    L: Integer;
  begin
    if Pointer(A) = Pointer(B) then Exit(True); // <-- HERE
    L := Length(A);
    if L <> Length(B) then Exit(False);
    Result := CompareMem(PInteger(A)^, PInteger(B)^, Sizeof(Integer) * L);
  end;

begin
  if not IsEqualIntegerDynArray(FGCodeLinePoints, Value) then
  begin
    FGCodeLinePoints := Value;
    Invalidate;
  end;
end;

Edited November 22, 2022 by Remy Lebeau

[David Heffernan 2345]

6 hours ago, Remy Lebeau said:

If there is any possibility that FGCodeLinePoints could be passed in to SetGCodeLinePoints() (eg: GCodeEditor1.GCodeLinePoints := GCodeEditor1.GCodeLinePoints;), then I would also add a pointer equality check as well, since dynamic arrays are implemented as ref-counted pinters, eg:

I'd definitely remove the pointer check you just added. Surely that's just going to make things slower. 

[Fr0sT.Brutal 900]

Guys you're saving on matches. CompareMem will eat all these nano-optimizations.