Playing with Entity System, performance and D.

[ag0aep6g via Digitalmars-d-learn]

On 06/19/2017 07:42 PM, SrMordred wrote:
> I was playing around my ES and different ways of doing it with D.
> 
> I end up with a performance test of alias func vs ranges vs opApply.
> 
> code here:
> https://dpaste.dzfl.pl/a2eff240552f
> 
> Results on my machine win 10 x64, compiling with:
> dub run --build=release --arch=x86 --compiler=ldc2
> (unable to test with gdc because 
> https://forum.dlang.org/thread/bfmbvxtnqfhhgquayrro@forum.dlang.org)
> 
> Alias func: ~40ms
> Range Type(front, popFront, emtpy): ~50ms
> OpApply: ~25ms
> 
> So first, if I make some really dumb relate to profiling speed or any D 
> code let me know!
> 
> 1) I thought that ranges were the fastest, but it got the least 
> performant code.

I don't think ranges are expected to be faster than the others.

> 2) opApply was faster than alias func. Its suprising for me.

For me, alias_fun and op_apply are very close. If anything, alias_fun 
seems to be slightly faster.

Typical output (ldc2 -release -O3):
----
36
Result(51)
44
Result(88)
37
Result(-127)
----

> 3) Not possible to return multiple values. So in the front() method I 
> Wrapped a node of pointers.(maybe a performance impact here?, there is a 
> better way of doing it? )

Avoiding bounds checking makes it faster for me (but is unsafe of course):

----
         return Node(&values.ptr[index_[0]], &results.ptr[index_[1]]);
----

Typical timing:

----
37
Result(74)
39
Result(113)
38
Result(-1)
----

Almost there, but still a bit slower than the others.

By the way, if I read it right, indexes is just `0 .. limit`, twice, 
isn't it? So there's no real point to it in the sample code. When I get 
rid of indexes and just count up to `limit`, all three versions perform 
the same. But I guess you're going to have arbitrary values in indexes 
when you actually use it.

> 4) there are no equivalent of declaring Type& x; (ref type) right?

Right. ref is only for parameters and returns. For variables, you have 
to user pointers.