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

[Daniel Kozak via Digitalmars-d-learn]

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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