is D so slow?

[bearophile]

baleog:
I suggest you to show the complete C and the complete D code.

>   float[] xs = new float[n*n];

With a smarter use of gc.malloc you may avoid clearing items two times...
(I presume the optimizer doesn't remove the first cleaning).
You can use this from the d.extra module of my libs:

import std.gc: gcmalloc = malloc, gcrealloc = realloc, hasNoPointers;

T[] NewVoidGCArray(T)(int n) {
    assert(n > 0, "NewVoidCGArray: n must be > 0.");
    auto pt = cast(T*)gcmalloc(n * T.sizeof);
    hasNoPointers(pt);
    return pt[0 .. n];
}


>   for(int i = n-1; i>=0; --i) {
>      xs[i] = 1.0;
>   }

D arrays know this shorter and probably faster syntax:
xs[] = 1.0;

Bye,
bearophile