Stanislav Blinov:
Unrolling everything except the loop in energy() seems to have
squeezed the bits neede to outperform c++, at least on my
machine :)
That should be impossible, as I remember from my old profilings
that energy() should use only an irrelevant amount of run time.
http://dpaste.dzfl.pl/45e98e476daf
While I benchmark some variants of this program I am seeing a
large variety of problems, limitations, bugs and regressions.
You latest D code crashes my ldc2 V.0.12.1, while 0.13.0-alpha1
compiles it. My older version of your D code runs with both
compiler versions, but V.0.12.1 generates faster code.
Plus you can't make those double2 immutable, you can't use vector
ops (because of performance, and also because they aren't nothrow
in V.0.12.1).
I was also experimenting with (note the align):
align(16) struct Body {
double[3] x, v;
double mass;
}
struct NBodySystem {
private:
__gshared static Body[5] bodies = [
// Sun.
Body([0., 0., 0.],
[0., 0., 0.],
solarMass),
...
But this improves the code for V.0.12.1 and worsens it for
0.13.0-alpha1.
Also I think the __gshared is ignored in V.0.12.1, but this bug
could be fixed in more recent versions of ldc2.
(I'm sticking to atoi because my copy of ldc seems to have an
issue in std.conv).
My version seems to use to!() correctly.
If ldc2 developers are reading this thread there is enough
strange stuff here to give one or two headaches :-)
Now I don't know what "final" version should I keep of this
program :-)
Bye,
bearophile
