Re: set constructor performance on Visual Studio 2003

"Marco Manfredini" <ok_nospam_ok@phoyd.net> wrote in message
news:fj740l$cbl$1@aioe.org...


...


I created a small test program where the size of the sets varies.
For visual express 2005 in release mode (and _HAS_ITERATOR_DEBUGGING set
to 0),
I get the following results:
filling 10000 sets of 1000 elements ... done in 5.031
filling 1000 sets of 10000 elements ... done in 6.078
filling 100 sets of 100000 elements ... done in 13.451
filling 10 sets of 1000000 elements ... done in 26.965
filling 1 set of 10000000 elements ... done in 36.917

This suggests that insertion of n sorted elements is not lineair with this
implementation.
When I modify the program to insert the values one by one, I get the same
timing.
So it seems that this implementation does not conform to the standard.

Another implementation of set (compiled with the same options) gives:
filling 10000 sets of 1000 elements ... done in 4.889
filling 1000 sets of 10000 elements ... done in 4.874
filling 100 sets of 100000 elements ... done in 4.874
filling 10 sets of 1000000 elements ... done in 4.875
filling 1 set of 10000000 elements ... done in 4.875

Here the function I used to test:

void settest()
{
   const size_t total_elements = 10000000;

   //
   // initialize an array with numbers to insert into the sets
   std::vector<size_t> numbers;
   for (size_t i = 0; i < total_elements; i++) numbers.push_back(i);

   for (size_t size = 1000; size <= total_elements; size *= 10)
   {
       size_t n_sets = total_elements / size;
       std::vector< std::set<size_t> > sets(n_sets);

       std::cout << "filling " << n_sets
                << (n_sets == 1? " set ": " sets ") << " of " << size
                << " elements ..." << std::flush;
       clock_t before = clock();

       for (size_t i = 0; i < n_sets; i++)
       {
           std::set<size_t> new_set(&numbers[0], &numbers[0] + size);
           new_set.swap(sets[i]); // prevent destruction
       }

       clock_t after = clock();
       std::cout << " done in "
           << double(after - before) / CLOCKS_PER_SEC << std::endl;
   }
}