Incoherent views of various storage order

[Mathieu Leocmach <mathieu.leocmach@…>]

I have a 256x258 array with only the first 256 lines of interest. The flatten memory block contains then 256 interesting values, 2 craps, 256 interesting values, 2 craps, etc.

I want to access each column of the interesting block, then each line. For this I use :

1. a view of the array with limited range in the second dimension
2. a view of line-major ordered array reference to the same block of memory, with limited range in the first dimension

Here is a test code:

#include <algorithm>
#include "boost/multi_array.hpp"

using namespace boost;
using namespace std;

int 
main () {
  // Create a 2D array that is 256 x 258
  typedef multi_array<float, 2> array_type;
  typedef multi_array_ref<float, 2> ref_type;
  typedef array_type::array_view<2>::type view_type;
  
  array<size_t, 3> paddedExt = {256,258};
  array_type A(paddedExt);
  
  /*Initialize the whole memory block with -1 */
  fill(A.origin(), A.origin()+A.num_elements(),-1.0);
  
  /*Fill the usefull part of the array by accessing data by column*/
  view_type B = A[indices[range()][range(0,256)]];
  for(view_type::iterator i=B.begin(); i!=B.end(); ++i)
    for(view_type::subarray<1>::type::iterator j=i->begin(); j!=i->end(); ++j)
      *j = 1.0;

  /*Access usefull data by line*/
  paddedExt[0]=258;
  paddedExt[1]=256;
  ref_type C(A.origin(), paddedExt, fortran_storage_order);
  view_type D = C[indices[range(0,256)][range()]];
  for(view_type::iterator i=D.begin(); i!=D.end(); ++i)
    for(view_type::subarray<1>::type::iterator j=i->begin(); j!=i->end(); ++j)
      output(*j);

return EXIT_SUCCESS;
}

This outputs a pretty high number of -1 ! More precisely, we have :

• 256 values
• 2 craps, 254 values
• 2 values, 2 craps, 252 values
• 4 values, 2 craps, 250 values
• etc.
• the last 2*256 good values are not output

It's like the views have lost their index_bases somewhere on the way.

I compiled and run this test under winXP, mingw32, gcc 3.4.5