prosty qsort openmp

template <class T,class comp>
T mediana (const T &a,const T &b,const T &c, comp cmp)
{
    if (cmp(a,b)) //a<b
    {
        if (cmp(b,c)) // a<b<c
            return b;
        else //b=max
            return (cmp(a,c))?c:a;
    } else//b<a
    {
        if (cmp(a,c)) // b<a<c
            return a;
        else //a=max
            return (cmp(b,c))?c:b;
    }

}

template <class iterator,class comp>
void par_sort(iterator begin, iterator end, comp cmp)
{

    int a= end-begin;

    if (end-begin<1000)
    {
        sort(begin, end, cmp);
    }
    else
    {

        iterator::value_type el_dzielacy =  mediana(*(begin + ((end-begin)/2)),*begin,*(end-1),cmp);
        iterator podzial = partition(begin, end, [=](const iterator::value_type &a ){return cmp(a,el_dzielacy);}  ) ;

        int aa=end-podzial;
        int bb= podzial-begin;
        if (aa==0 || bb==0)
        {
            sort(begin,end);
            return;
        }

        #pragma omp parallel sections
        {
            #pragma omp section
                 par_sort( podzial,  end,  cmp);
            #pragma omp section
                 par_sort( begin, podzial,  cmp);
        }

    }

}