native/stencil.h

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#ifndef GRPPI_NATIVE_STENCIL_H
#define GRPPI_NATIVE_STENCIL_H

#include "parallel_execution_native.h"
#include "../common/iterator.h"

namespace grppi {

template <typename InputIt, typename OutputIt, typename StencilTransformer, 
          typename Neighbourhood>
void stencil(parallel_execution_native & ex, 
             InputIt first, InputIt last, OutputIt first_out, 
             StencilTransformer transform_op, Neighbourhood neighbour_op) 
{
  using namespace std;

  vector<thread> tasks;
  int size = distance(first,last);
  int elements_per_thread = size/ex.concurrency_degree();
 
  for (int i=1; i<ex.concurrency_degree(); ++i) {
    auto begin = first + (elements_per_thread * i);
    auto end = (i==ex.concurrency_degree()-1)?
        last :
        next(first, elements_per_thread * (i+1));

    auto out = first_out + (elements_per_thread * i);

    tasks.emplace_back([&](InputIt begin, InputIt end, OutputIt out) {
      auto manager = ex.thread_manager();

      while (begin!=end) {
        *out = transform_op(begin, neighbour_op(begin));
        begin++;
        out++;
      }
    }, 
    begin, end, out);
  }

  auto end = first + elements_per_thread;
  while(first!=end){
    *first_out = transform_op(first, neighbour_op(first));
    first++;
    first_out++;
  }

  for (auto && t : tasks) { t.join(); }
}

template <typename InputIt, typename OutputIt, typename StencilTransformer, 
          typename Neighbourhood, typename ... OtherInputIts>
void stencil(parallel_execution_native & ex, 
             InputIt first, InputIt last, OutputIt first_out, 
             StencilTransformer transform_op, Neighbourhood neighbour_op, 
             OtherInputIts ... other_firsts ) 
{
  using namespace std;

  vector<thread> tasks;
  int size = last - first;
  int elements_per_thread = size/ex.concurrency_degree();

  for (int i=1; i<ex.concurrency_degree(); i++){
  auto begin = first + (elements_per_thread * i);
  auto end = (i==ex.concurrency_degree()-1)?
      last :
      first + elements_per_thread * (i+1);

  auto out = first_out + (elements_per_thread * i);
        
  tasks.emplace_back(
    [&](InputIt begin, InputIt end, OutputIt out, int i, int n, OtherInputIts ... other_firsts){
      auto manager = ex.thread_manager();

      advance_iterators(n*i, other_firsts ...);
      while (begin!=end) {
        *out = transform_op(begin, neighbour_op(begin,other_firsts...));
        begin++;
        advance_iterators(other_firsts ... );
        out++;
      }
    },
    begin, end, out, i, elements_per_thread,other_firsts ...);
  }

  auto end = first + elements_per_thread;
  while (first!=end) {
    *first_out = transform_op(*first, neighbour_op(first,other_firsts...));
    first++;
    advance_iterators( other_firsts ... );
    first_out++;
  }


  for (auto && t : tasks) { t.join(); }
}

}
#endif