J3/06-330

Date: October 27, 2006
To: J3
From: Aleksandar Donev
Subject: Integration of autotargetting and contiguous rank remapping
Reference: J3/06-007r1
Dependencies: None

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Specification
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The new autotargetting feature (magically pointing dummy
pointers to non-pointer actual targets) is not integrated with
pointer array rank-remapping of contiguous targets, and also with
bounds-remapping. Specifically, the autotargetting feature requires
that the ranks of the dummy and actual agree (see [316:1]), and
always uses the same lower bounds as those of the target. This
paper proposes to allow contiguous actuals of any rank when the
dummy is a rank-1 pointer. The bounds of the dummy are set to 1 and
SIZE(actual). Example:

interface
   subroutine process(x)
      real, pointer, contiguous :: x(:)
   end subroutine
end interface

real :: y(10,10)
call process(y) ! The bounds of x are [1,100]

The reason for this lack of integration is that there is no place to
put lower or upper bounds as required to perform pointer rank-remapping
or bounds-remapping [see <bounds-spec-list> or <bounds-remapping-list>
in R735]. However, for one particular and very common case, when the
dummy is rank-1, the bounds are obvious, [1,SIZE(actual)]. That is,
the autotargetting feature would use the rank-remapping:

ptr_dummy[1:size(contig_actual)]=>contig_actual

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Note: As a further alternative, we may wish to consider allowing one
to specify lower bounds for pointer dummies, though this paper does
not propose that. Example:

interface
   subroutine process(x)
      real, pointer, contiguous :: x(1:)
         ! Lower bound is always 1 regardless of actual
   end subroutine
end interface

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Edits:
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[315:30] In the sentence "Otherwise..." add "X" after "actual argument"
and "P" after "dummy pointer".

[315:31] After "an assignment statement." add a new sentence:
"If the ranks of the dummy and actual arguments differ, the dummy
shall be a rank-1 array and the actual shall be contiguous (5.3.6)."

[315:32] Add to the end of the paragraph:
"as if the statement P=>X were executed for the case when the ranks
of the dummy and actual arguments agree, or otherwise, the statement
P(1:SIZE(X))=>X were executed.

[316:1] Delete "and ranks"