28.12.2014 17:36, Michael Van Canneyt пишет:
On Sun, 28 Dec 2014, Mattias Gaertner wrote:
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;
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;
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
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