this one is even faster than c++:

http://ideone.com/TRDsOo

On Sun, Aug 13, 2017 at 10:00 AM, Daniel Kozak <kozzi11@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@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@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@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).