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

[jerro]

On Tuesday, 17 April 2012 at 01:30:30 UTC, ReneSac wrote:
> On Monday, 16 April 2012 at 22:58:08 UTC, Timon Gehr wrote:
>> On 04/17/2012 12:24 AM, ReneSac wrote:
>>> Windows.
>>>
>>
>> DMC runtime !
> DMC = Digital Mars Compiler? Does Mingw/GDC uses that? I think 
> that both, g++ and GDC compiled binaries, use the mingw 
> runtime, but I'm not sure also.
>
>> 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.
> Ok, I will benchmark on linux latter.
>
>> 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.
> Yeah, I'm comparing the implementation, and I made it clear 
> that it may be the GDC front-end that may be the "bottleneck".
>
> And I don't think it is I/O bound. It is only around 10MB/s, 
> whereas my HD can do ~100MB/s. Furthermore, on files more 
> compressible, where the speed was higher, the difference 
> between D and C++ was higher too. And if is in fact I/O bound, 
> then D is MORE than 50% slower than C++.
>
>> The difference is likely because of differences in external C 
>> libraries.
> Both, the D and C++ versions, use C's stdio library. What is 
> the difference?

Have you tried profiling it? On Windows you can use AMD 
CodeAnalyst for that, it works pretty well in my experience and 
it's free of charge.