ISO/IEC JTC1/SC22/WG5 N1531

	            
                         Storage size


                         Richard Maine

In response to a public comment, paper J3/03-108r3 added three
new named constants to ISO_FORTRAN_ENV.  I have no objection
to the addition of FILE_STORAGE_SIZE.  However, for the other
two, I strongly feel that this is something that we should do
correctly if we are going to do it at all.

We are adding a new feature that not only is obsolete now - it
was obsolete two revisions of the standard ago.  The proposed
constants NUMERIC_STORAGE_SIZE and CHARACTER_STORAGE_SIZE would
have been adequate for f77.  As of f90, they are woefuly
inadequate.  Why are we adding new features to f2k that support
only f77 code and are all but useless for code that follows most
style recommendations for f90 code?  Are we prepared to explain
our answer to that question when it gets asked by users, as it
most certainly will be?  When that happens, don't expect me to
defend the feature.

I do not find the argument that "this is what someone asked for"
to be very convincing.  People ask for lots of things that they
don't get.  We need to apply our best judgement in answering
requests - not just limit the answers to yes or no.  In this
case, a solution that I consider good is quite doable.  We can do
the job in a way that provides both the requested functionality
and also use useful for newer coding styles.  It isn't
particularly difficult to do that.  If we don't think this
feature is worth the small amount of work to do that way, or if a
majority thinks that it is harder than I do, then I don't think
we should do it at all.

I propose that we add the function below as a more complete
solution for this useful functionality.  Many, if not most,
implementations already have a smilar function.  I have avoided
the most common current names for it specifically to avoid
potential conflicts in points of detail....and that allows me
to do one thing in what I consider to be a more robust way
(we will return the size in bits instead of in octets).

This function could be added either as an intrinsic or as a
module procedure in ISO_FORTRAN_ENV.  I came down slightly on the
side of doing it as an intrinsic, but it was a close call.  The
edits below are for that approach.  If a majority finds it more
appropriate in the module, that is an easy change and one I'd find
acceptable.  Other choices for the function name would also be
acceptable.

The proposed function allows array arguments, but always returns
the size of a scalar of the type.  The standard adequately
defines the storage requirements for arrays in terms of those for
scalars, so I see no need for array-related functionality in this
function.  I consider the proposed function similar to the LEN
intrinsic in this regard (LEN accepts array arguments, but
returns the length of an element rather than the length of the
whole array).

The proposed function works on the dynamic type of its argument.
An unpublished first draft used the declared type for simplicity,
but I realized that handling len type parameters requires
run-time evaluation in some cases anyway, so we might as well go
with the dynamic type as slightly more flexible.  It is not
absolutely essential that polymorphic arguments be allowed at
all.  If that is deemed too much complication, we could prohibit
them.  But it seems to me that they do work out pretty well.

The edits below delete the NUMERIC_STORAGE_SIZE and
CHARACTER_STORAGE_SIZE constants, because the function is more
general.  If one wanted to have both the constants and the
function, I wouldn't object too strongly.  That wouldn't be my
first choice, but it is well within bounds that I'd consider
reasonable as a compromise.

I. Addition of the function

  [127:41+] Add list item

    (4a) the inquiry function STORAGE_SIZE,

  [298:19+] Add line

     "STORAGE_SIZE (X)        Storage size in bits"

  [356:1+] Add section

    13.7.115a STORAGE_SIZE (X)

      Description.  Returns the storage size in bits for a
      nonpointer scalar of the declared type of X.

      Class.  Inquiry function.

      Argument.  X may be of any type.  It shall not be unlimited
      polymorphic.  If it is an unallocated allocatable or a
      disassociated pointer, it shall have no deferred type
      parameters.  It shall not be a pointer with undefined
      association status.  It may be a scalar or an array.

      Result Characteristics.  Default integer scalar.

      Result Value.  The result value is the size in bits of the
      storage unit (16.4.3.1) for a nonpointer scalar with the
      dynamic type and type parameters of X.

      Example.  STORAGE_SIZE(1.0) returns the number of bits in the
      numeric storage unit.

  [417:36-38] "The sizes...(13.8.2.3)" ->
     "The size of the file storage unit is given by the constant
      FILE_STORAGE_SIZE (13.8.2.3.3).  The sizes of the character
      storage unit, numeric storage unit, and unspecified storage
      units can be determined using the intrinsic function
      STORAGE_SIZE (13.7.115a)."

II. Deletion of the constants

  These edits assume that 13.8.2 has been simplified as described in
  part 1 of my paper titled ISO_FORTRAN_ENV.  If that isn't done,
  then other trivial changes are needed in the sentence that forms the
  body of 13.8.2.3, and the 13.8.2.3.3 section heading should
  probably be deleted (or promoted).

  [362:28-33] Delete sections 13.8.2.3.1 and 13.8.2.3.2.