D outperformed by C++, what am I doing wrong?

[Daniel Kozak via Digitalmars-d-learn]

this one is even faster than c++:
http://ideone.com/TRDsOo

On Sun, Aug 13, 2017 at 10:00 AM, Daniel Kozak <kozzi11 at gmail.com> wrote:

> my second version on ldc takes 380ms and c++ version on same compiler
> (clang), takes 350ms, so it seems to be almost same
>
> On Sun, Aug 13, 2017 at 9:51 AM, amfvcg via Digitalmars-d-learn <
> digitalmars-d-learn at puremagic.com> wrote:
>
>> On Sunday, 13 August 2017 at 07:30:32 UTC, Daniel Kozak wrote:
>>
>>> Here is more D idiomatic way:
>>>
>>> import std.stdio : writeln;
>>> import std.algorithm.comparison: min;
>>> import std.algorithm.iteration: sum;
>>> import core.time: MonoTime, Duration;
>>>
>>>
>>> auto sum_subranges(T)(T input, uint range)
>>> {
>>>     import std.array : array;
>>>     import std.range : chunks, ElementType;
>>>     import std.algorithm : map;
>>>
>>>     if (range == 0)
>>>     {
>>>         return ElementType!(T)[].init;
>>>     }
>>>     return input.chunks(range).map!(sum).array;
>>> }
>>>
>>> unittest
>>> {
>>>     assert(sum_subranges([1,1,1], 2) == [2, 1]);
>>>     assert(sum_subranges([1,1,1,2,3,3], 2) == [2, 3, 6]);
>>>     assert(sum_subranges([], 2) == []);
>>>     assert(sum_subranges([1], 2) == [1]);
>>>     assert(sum_subranges([1], 0) == []);
>>> }
>>>
>>>
>>> int main()
>>> {
>>>     import std.range : iota, array;
>>>     auto v = iota(0,1000000);
>>>     int sum;
>>>     MonoTime beg = MonoTime.currTime;
>>>     for (int i=0; i < 100; i++)
>>>         sum += cast(int)sum_subranges(v,2).length;
>>>     MonoTime end = MonoTime.currTime;
>>>     writeln(end-beg);
>>>     writeln(sum);
>>>     return sum;
>>> }
>>>
>>> On Sun, Aug 13, 2017 at 9:13 AM, Daniel Kozak <kozzi11 at gmail.com> wrote:
>>>
>>> this works ok for me with ldc compiler, gdc does not work on my arch
>>>> machine so I can not do comparsion to your c++ versin (clang does not work
>>>> with your c++ code)
>>>>
>>>> import std.stdio : writeln;
>>>> import std.algorithm.comparison: min;
>>>> import std.algorithm.iteration: sum;
>>>> import core.time: MonoTime, Duration;
>>>>
>>>>
>>>> T[] sum_subranges(T)(T[] input, uint range)
>>>> {
>>>>     import std.array : appender;
>>>>     auto app = appender!(T[])();
>>>>     if (range == 0)
>>>>     {
>>>>         return app.data;
>>>>     }
>>>>     for (uint i; i < input.length; i=min(i+range, input.length))
>>>>     {
>>>>         app.put(sum(input[i..min(i+range, input.length)]));
>>>>     }
>>>>     return app.data;
>>>> }
>>>>
>>>> unittest
>>>> {
>>>>     assert(sum_subranges([1,1,1], 2) == [2, 1]);
>>>>     assert(sum_subranges([1,1,1,2,3,3], 2) == [2, 3, 6]);
>>>>     assert(sum_subranges([], 2) == []);
>>>>     assert(sum_subranges([1], 2) == [1]);
>>>>     assert(sum_subranges([1], 0) == []);
>>>> }
>>>>
>>>>
>>>> int main()
>>>> {
>>>>     import std.range : iota, array;
>>>>     auto v = iota(0,1000000).array;
>>>>     int sum;
>>>>     MonoTime beg = MonoTime.currTime;
>>>>     for (int i=0; i < 100; i++)
>>>>         sum += cast(int)sum_subranges(v,2).length;
>>>>     MonoTime end = MonoTime.currTime;
>>>>     writeln(end-beg);
>>>>     writeln(sum);
>>>>     return sum;
>>>> }
>>>>
>>>> On Sun, Aug 13, 2017 at 9:03 AM, Neia Neutuladh via Digitalmars-d-learn
>>>> < digitalmars-d-learn at puremagic.com> wrote:
>>>>
>>>> [...]
>>>>>
>>>>
>> Thank you all for the replies. Good to know the community is alive in d :)
>>
>> Let's settle the playground:
>> D  : http://ideone.com/h4fnsD
>> C++: http://ideone.com/X1pyXG
>>
>> Both using GCC under the hood.
>> C++ in 112 ms;
>> D in :
>> - 2.5 sec with original source;
>> - 2.5 sec with Daniel's 1st version;
>> - 5 sec timeout exceeded with Daniel's 2nd version;
>> - 1.8 sec with Neia-like preallocation;
>>
>> So still it's not that neaty.
>>
>> (What's interesting C++ code generates 2KLOC of assembly, and Dlang @ ldc
>> 12KLOC - checked at godbolt).
>>
>> P.S. For C++ version to work under clang, the function which takes
>> (BinaryOp) must go before the other one (my bad).
>>
>
>
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