Class ParallelMergeRange

perf/perf_tbb_merge.cpp:23–53

template<typename Iterator>
struct ParallelMergeRange {
    static size_t grainsize;
    Iterator begin1, end1; // [begin1,end1) is 1st sequence to be merged
    Iterator begin2, end2; // [begin2,end2) is 2nd sequence to be merged
    Iterator out;               // where to put merged sequence
    bool empty()   const {return (end1-begin1)+(end2-begin2)==0;}
    bool is_divisible() const {
        return (std::min)( end1-begin1, end2-begin2 ) > grainsize;
    }
    ParallelMergeRange( ParallelMergeRange& r, split ) {
        if( r.end1-r.begin1 < r.end2-r.begin2 ) {
            std::swap(r.begin1,r.begin2);
            std::swap(r.end1,r.end2);
        }
        Iterator m1 = r.begin1 + (r.end1-r.begin1)/2;
        Iterator m2 = std::lower_bound( r.begin2, r.end2, *m1 );
        begin1 = m1;
        begin2 = m2;
        end1 = r.end1;
        end2 = r.end2;
        out = r.out + (m1-r.begin1) + (m2-r.begin2);
        r.end1 = m1;
        r.end2 = m2;
    }
    ParallelMergeRange( Iterator begin1_, Iterator end1_,
                        Iterator begin2_, Iterator end2_,
                        Iterator out_ ) :
        begin1(begin1_), end1(end1_),
        begin2(begin2_), end2(end2_), out(out_)
    {}
};

template<typename Iterator>
size_t ParallelMergeRange<Iterator>::grainsize = 1000;