[phobos] Ndslice speed

[Daniel Murphy via phobos]

It may help to turn dmd's optimizer and inliner on - "dmd -inline
-release -O -boundscheck=off".

On Sun, Aug 28, 2016 at 5:43 AM, Matthias Redies via phobos
<phobos at puremagic.com> wrote:
> Hello,
>
> I've come across the library experimental.ndslice, which is supposed to
> mimic NumPy. In order to test it I wrote a very crude matrix multiplication:
>
> http://pastebin.com/Ew4u2iVz
>
> and for comparison I also implemented it in Fortran90:
>
> http://pastebin.com/6afnVyZF
>
> Then I used linux's "time" command to time them each:
>
> ifort test.f90 && time ./a.out
>          600
>
> real    0m0.154s
> user    0m0.148s
> sys     0m0.004s
>
>
> dmd test.d  && time ./test
> 1.16681e+08
> 600   600
>
> real    0m6.770s
> user    0m6.772s
> sys     0m0.004s
>
>
> I understand that dmd is not optimized for speed, but in the end both do
> basically the same thing. Both implement 2D array and both array types
> include the size of the array (unlike C). Given that both are compiled
> languages the difference seems to be unreasonably large.
>
> If I turn on boundschecking for Fortran I get:
>
> ifort -check all test.f90 && time ./a.out
>          600
>
> real    0m6.049s
> user    0m6.044s
> sys     0m0.004s
>
>
> which is roughly the speed difference I'd expect, but if I use the
> -boundscheck=off option for dmd that doesn't help. Am I using ndslice
> correctly? Why is the speed difference so large? How do I speed it up?
>
> Kind regards
>
> Matthias
>
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