Hi all,
I'm solving below task:
given container T and value R return sum of R-ranges over T. An
example:
input : T=[1,1,1] R=2
output : [2, 1]
input : T=[1,2,3] R=1
output : [1,2,3]
(see dlang unittests for more examples)
Below c++ code compiled with g++-5.4.0 -O2 -std=c++14 runs on my
machine in 656 836 us.
Below D code compiled with dmd v2.067.1 -O runs on my machine in
~ 14.5 sec.
Each language has it's own "way of programming", and as I'm a
beginner in D - probably I'm running through bushes instead of
highway. Therefore I'd like to ask you, experienced dlang devs,
to shed some light on "how to do it dlang-way".
C++ code:
#include <algorithm>
#include <chrono>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <string>
#include <utility>
#include <numeric>
#include <vector>
template<typename T, typename K>
std::vector<K> sum_elements(const T& beg, const T& end,
std::size_t k, K def)
{
if (k == 0) {
return std::vector<K>{};
}
return sum_elements(beg, end, k, def, [](auto &l, auto &r){
return r+l;});
}
template<typename T, typename K, class BinaryOp>
std::vector<K>
sum_elements(
const T& beg,
const T& end,
std::size_t k,
K def,
BinaryOp op)
{
std::vector<K> out;
out.reserve((std::distance(beg, end) - 1)/k + 1);
for (auto it = beg; it!=end; std::advance(it,
std::min(static_cast<std::size_t>(std::distance(it, end)), k)))
{
out.push_back(std::accumulate(it, std::next(it,
std::min(static_cast<std::size_t>(std::distance(it, end)), k)),
def, op));
}
return out;
}
int main()
{
std::vector<int> vec;
auto size = 1000000;
vec.reserve(size);
for (int i=0; i < size; ++i)
vec.push_back(i);
auto beg = std::chrono::system_clock::now();
auto sum = 0;
for (int i=0; i < 100; i++)
sum += sum_elements(vec.begin(), vec.end(), 2, 0).size();
auto end = std::chrono::system_clock::now();
std::cout <<
std::chrono::duration_cast<std::chrono::microseconds>(end-beg).count() << std::endl;
std::cout << sum << std::endl;
return sum;
}
D 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)
{
T[] result;
if (range == 0)
{
return result;
}
for (uint i; i < input.length; i=min(i+range, input.length))
{
result ~= sum(input[i..min(i+range, input.length)]);
}
return result;
}
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()
{
int[1000000] v;
for (int i=0; i < 1000000; ++i)
v[i] = i;
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;
}
