Small part of a program : d and c versions performances diff.

[Kapps via Digitalmars-d-learn]

Measure a larger number of loops. I understand you're concerned 
about microseconds, but your benchmark shows nothing because your 
timer is simply not accurate enough for this. The benchmark that 
bearophile showed where C took ~2 nanoseconds vs the ~7000 D took 
heavily implies to me that the C implementation is simply being 
optimized out and nothing is actually running. All inputs are 
known at compile-time, the output is known at compile-time, the 
compiler is perfectly free to simply remove all your code and 
replace it with the result. I'm somewhat surprised that the D 
version doesn't do this actually, perhaps because of the dynamic 
memory allocation. I realize that you can't post your actual 
code, but this benchmark honestly just has too many flaws to 
determine anything from.

As for startup cost, D will indeed have a higher startup cost 
than C because of static constructors. Once it's running, it 
should be very close. If you're looking to start a process that 
will run for only a few milliseconds, you'd probably want to not 
use D (or avoid most static constructors, including those in the 
runtime / standard library).