------- Comment #1 from burnus at gcc dot gnu dot org 2010-02-04 19:32 -------
> so, we check if the array-size is empty, ubound - lbound < 0. In that
> case we set size to zero. Otherwise we compute it
> as (ubound - lbound + 1) *8.
> Then we check whether size is negative and error out.
> Then we actually allocate max(1,size).
The reason for the setting it to zero is that Fortran allows one to allocate a
zero-sized array: ALLOCATE ( Array(0:-2) )
The reason for MAX(1, size) is to make ALLOCATE(A(1:0)); if(ALLOCATED(A))
work. (This was added later than "size < 0 ? 0 : size".)
Why there is a negative check? Well, I do not know. I also can speculate about
a poor man's overflow check, which sometimes indeed works, but often fails.
* * *
> Why not simply do
> size = (ubound - lbound + 1) * 8;
> malloc (size);
I think that would be the future: With the array descriptor (dope vector)
reform, we will have an "allocated" field and thus one can do:
descriptor.allocated = true
descriptor.data = malloc (max (0,size))
Where "if(allocated(A))" translates into "if(A.allocated)".
Actually, maybe one should better use:
size = (ubound - lbound + 1)
if (size > 0)
{
descriptor.data = malloc(size)
if (descriptor.data == NULL)
error ("allocate failed");
}
descriptor.allocated = true
The "allocated" member of the descriptor is also needed in order to make the
following work properly:
integer, target :: int
integer, pointer :: ptr
ptr => int
deallocate(ptr, stat=i) ! shall return "i != 0" but not crash
Thus, from my side: The negative check should be removed and the simplified
version should be applied after the descriptor update. Before the descriptor
update (planned for 4.6, breaks ABI) one can use:
size = (ubound - lbound + 1) * 8;
malloc (max(1,size));
Paul, what do you think?
(PS: POSIX Allows "ptr = malloc(0); free(ptr)", where "malloc(0)" returns
either NULL or a unique pointer.)
--
burnus at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |pault at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42958
