array2D::resize() is not optimal

Walter Daems <[email protected]> Wed, 21 Apr 2004 14:45:58 +0200

Newsgroups	gmane.comp.lib.mtl.devel
Message-ID	<[email protected]>

Hi all,

The function array2D::resize() is not optimal in its current form:
- it ruins sparsity
      if the OneD-s of the array2D are sparse.
- it does some initializations that are purposeless
      if the OneD-s of the array2D are dense

The patch in attachment solves these problems. The speed in case
of dense OneD-s might be somewhat degraded because of the extra
it.index() < n check, but :
- I guess resizing is to be considered an expensive operation anyway.
- the original function contained already unnecessary overhead
   ( the third for loop had no purpose whatsoever )

bye,

Walter.

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patch_resize (text/plain, 1.5 KB)

*** orig/array2D.h	2004-04-20 13:48:41.000000000 +0200
--- adpt/array2D.h	2004-04-21 14:41:41.000000000 +0200
***************
*** 346,369 ****
  
    /* JGS add sub_matrix */
  
    void resize(size_type m, size_type n) {
      rep_ptr newrep = new rep_type(m);
!     { for (typename rep_type::iterator i = newrep->begin();
! 	   i != newrep->end(); ++i)
        *i = OneD(n);
!     }
      size_type M = MTL_MIN(m, dim.first());
      size_type N = MTL_MIN(n, dim.second());
      size_type i, j;
      for (i = 0; i < M; ++i)
!       for (j = 0; j < N; ++j)
! 	(*newrep)[i][j] = (*rep)[i][j];
!     
!     for (; i < m; ++i)
!       for (; j < n; ++j)
! 	(*newrep)[i][j] = T();
  
      rep = newrep;
      dim = dim_type(m, n);
    }
  
--- 346,371 ----
  
    /* JGS add sub_matrix */
  
    void resize(size_type m, size_type n) {
      rep_ptr newrep = new rep_type(m);
!     for (typename rep_type::iterator i = newrep->begin();
!          i != newrep->end(); ++i)
        *i = OneD(n);
!     
      size_type M = MTL_MIN(m, dim.first());
      size_type N = MTL_MIN(n, dim.second());
      size_type i, j;
      for (i = 0; i < M; ++i)
!       {
!         typename OneD::const_iterator       it    = (*rep)[i].begin();
!         const typename OneD::const_iterator endit = (*rep)[i].end();
! 
!         for ( ; it != endit; ++it )
!           if ( it.index() < n )
!             (*newrep)[i][it.index()] = *it;
!       }
  
      rep = newrep;
      dim = dim_type(m, n);
    }