Re: 991108.11 Fortran 90 arrays - a couple of questions

[James Cownie <jcownie at etnus dot com>]

> program main
> 
>    type t_1
>      integer a
>      real b
>    end type
> 
>    type(t_1), target, dimension(3,2) :: s_1
>    integer, pointer, dimension(:,:) :: x
> 
>    x => s_1%a         ! (1)
> 
> end program main
> 
> There are two issues regarding the use of DW_AT_stride that this example
> might clarify:
>  
> a) For pointers to arrays where the distance between successive elements of an 
>    array is different from the actual element size as defined by the element
>    type DIE.
> b) For Multi-dimensional arrays, where the distance between successive elements 
>    along a given dimension is required.

To make it even _more_ interesting, you might consider changing 
your example marginally to something like this :-

program main

   type t_1
     complex a
     integer b
   end type

   type(t_1), target, dimension(3,2) :: s_1
   complex, pointer, dimension(:,:) :: x

   x => s_1%a         ! (1)

end program main

In this case, the distance between the s_1%a elements will very likely
be _less_ than the size of a complex variable. (It is an example like
this which demonstrates why the stride must be specified in bytes,
rather than the size of the scalar object).

> Where the DW_AT_stride expressions result in the number of bytes between
> successive elements along the given dimension, 
> 
> stride_1 = multiplier_1*scale_factor, 
> stride_2 = multiplier_2*scale_factor.
> 
> So that the address of x(i,j) can be calculated as:
> 
> address of x(i,j) = base_address 
>                     + stride_1*(i - lower_bound_1) 
>                     + stride_2*(j - lower_bound_2)
> 
> Have I got the right interpretation of DW_AT_stride? 

Exactly. 

-- Jim 

James Cownie	<jcownie@etnus.com>
Etnus, Inc.     +44 117 9071438
http://www.etnus.com