Hi,

forwarded from Zeljko:

It's about fpc issue
http://bugs.freepascal.org/view.php?id=26370

It seems that TVariantArrayIterator.AtEnd loops for all Dims for no reason, so have impact on performance.

*current implementation*
function TVariantArrayIterator.AtEnd: Boolean;
var
   i : sizeint;
begin
   result:=false;
   for i:=0 to Pred(Dims) do
     if Coords^[i] >= Bounds^[i].LowBound + Bounds^[i].ElementCount then
       result:=true;
end;
*optimized implementation*
function TVariantArrayIterator.AtEnd: Boolean;
var
   i : sizeint;
begin
   result:=false;
   for i:=0 to Pred(Dims) do
     if Coords^[i] >= Bounds^[i].LowBound + Bounds^[i].ElementCount then
     begin
       result:=true;
       break;
     end;
end;

Thanks.

Mattias

Or, better yet

var
   i : sizeint;
begin
   Result:=false;
   I:=0;
   While (Not Result) and (I<=Pred(Dims)) do
     begin
     Result:= Coords^[i] >= Bounds^[i].LowBound + Bounds^[i].ElementCount;
     Inc(I);
     end;
end;

People really don't seem to get booleans, and why they scorn "While" is beyond me. All these ugly "break" statements :(

You may optimize even more by calculating Max:=pred(dims) once and doing I<=Max;

Michael.

28.12.2014 17:36, Michael Van Canneyt пишет:

Actually, in this particular case performance optimizations are pretty useless:
- TVariantArrayIterator.AtEnd method is called just once to decide whether it is necessary to iterate the array. Its usage is not typical for iterators, where such methods are called in a loop.
- To return False, it has to iterate all dimensions. After that, iterating the data of variant array will take orders of magnitude more time.
- Early exit can happen only for arrays with zero-sized dimension, which is basically invalid and indicates programmer's mistake elsewhere.

Regards,
Sergei

All this may of course be true for this particular case, but it's in general always better to have optimized code. So I have committed the code as I replied it (after testing that the test program still performs as expected).

Michael.

[...] People really don't seem to get booleans, and why they scorn "While" is beyond me. All these ugly "break" statements :( You may optimize even more by calculating Max:=pred(dims) once and doing I<=Max;

Isn't "for" easier to optimize for the compiler than "while".

Mattias

Now you're asking too much, I do not know this. At least the for code has 2 branches more than my code :)

Michael.