11-108
To: J3
From: Nick Maclaren
Subject: Interop TR: dim member validity
Date: 2011 January 20
Reference: 10-251.pdf, 10-235



This issue was raised in 10-235, but there are no minutes of the
subgroup, so I do not know what happened and what decisions were taken.
Because of that, this merely raises the issue and provides no edits.

Even if the approach in 10-235 is not taken, the issue of constraints on
what dim values can be passed from C to Fortran needs to be resolved.
As I understand it, the constraints on the extent and sm fields are as I
described in 10-235:

    All strides in the bounds array shall be non-zero.  There shall be a
    reordering of the dimensions such that the absolute value of the
    stride of one dimension is not less than the absolute value of the
    stride of the previous dimension multiplied by the extent of the
    previous dimension.

There is nothing in 10-251.pdf/N1838.pdf that requires that.  It does
not even require distinct elements not to alias each other, as in:

    elem_len = 1
    dim[0].extent = 100
    dim[0].sm = 2
    dim[1].extent = 100
    dim[2].sm = 5

A nastier case is descriptors where no elements overlap but dimensions
do - which begs the question of whether Fortran compilers should be
required to accept such descriptors, diagnose them, or what?  For
example:

    elem_len = 8
    dim[0].extent = 10
    dim[0].sm = 88
    dim[1].extent = 10
    dim[2].sm = 104