D 50% slower than C++. What I'm doing wrong?

[Timon Gehr]

On 04/17/2012 12:24 AM, ReneSac wrote:
> On Monday, 16 April 2012 at 07:28:25 UTC, Andrea Fontana wrote:
>> Are you on linux/windows/mac?
>
> Windows.
>

DMC runtime !

> My main question is now *WHY* D is slower than C++ in this program? The
> code is identical (even the same C functions)

No. They are not the same. The performance difference is probably 
explained by the dmc runtime vs. glibc difference, because your biased 
results are not reproducible on a linux system where glibc is used for 
both versions.

> in the
> performance-critical parts, I'm using the "same" compiler backend
> (gdc/g++), and D was supposed to a fast compilable language.

/was/is/s

> Yet it is up to 50% slower.
>

This is a fallacy. Benchmarks can only compare implementations, not 
languages. Furthermore, it is usually the case that benchmarks that have 
surprising results don't measure what they intend to measure. Your 
program is apparently rather I/O bound.

> What is D doing more than C++ in this program, that accounts for the
> lost CPU cycles?
> Or what prevents the D program to be optimized to the
> C++ level? The D front-end?

The difference is likely because of differences in external C libraries.