Slow performance compared to C++, ideas?

[Kiith-Sa]

Profile.

Don't even think of asking for help before profiling. Those bugs 
you fixed here would be trivial to detect with a profiler. 
GC-dependent stuff usually is (like array literals mentioned 
here) usually are.

As for profiling of something like this, both gprof and DMD's 
builtin profiler are probably going to be useless. Use perf (if 
on Linux), or AMD CodeAnalyst, or some other sampling profiler 
(these two are free).