J3/00-308

  Date:  11-Oct-2000
  To:    J3
  From:  Stan Whitlock
  Subj:  When default KIND isn't good enough

  Some of us implement Fortran 95 on 64-bit machines.  In my case
  on Compaq Alpha hardware, that means:

    o   there is a 64-bit integer, KIND=8

    o   default integer is 32-bit, KIND=4

    o   arrays can have dimensions longer that 2**31

    o   CHARACTER strings can have lengths longer than 2**31

    o   addresses are 64-bits so Cray-style POINTERs are 64-bits

  It doesn't take a 64-bit machine to run into limitations on Fortran
  95's default integer but a 64-bit machine makes them really obvious.

  Here are the extensions we made to Compaq Fortran to accomodate
  64-bit hardware:

    o   There is a set of Fortran 95 intrinsics that return default
        integer according to the Fortran Standard but have to be able
        to return a bigger integer value for large data:

                LEN (string
                     [,KIND=scalar-integer-initialization-expression])
                SIZE (array [,dim] [,KIND=s-i-i-e])
                SHAPE (source [,KIND=s-i-i-e])
                LBOUND (array [,dim] [,KIND=s-i-i-e])
                UBOUND (array [,dim] [,KIND=s-i-i-e])
                MAXLOC (array, dim [,mask] [,KIND=s-i-i-e])
                MAXLOC (array [,mask] [,KIND=s-i-i-e])
                MINLOC (array, dim [,mask] [,KIND=s-i-i-e])
                MINLOC (array, dim [,mask] [,KIND=s-i-i-e])
                INDEX (string, substring [,back] [,KIND=s-i-i-e])
                LEN_TRIM (string [,KIND=s-i-i-e])
                SCAN (string, set [,back] [,KIND=s-i-i-e])
                VERIFY (string, set [,back] [,KIND=s-i-i-e])

    o   Several keywords on INQUIRE and READ take default integer
        according to the Fortran Standard.  They are

                INQUIRE (RECL= , NEXTREC= )
                READ (SIZE= )

        These specify integer variables that the I/O library stores
        into.  These keywords were extended to allow INTEGER(8)
        targets.

    o   Notice that READ (REC= ) takes an integer-expression so its
        kind is not an issue and we didn't have to do anything
        special.  This is also true for subscript and substring
        expressions etc.

    o   We support Cray-style POINTERs as an extension so we defined
        the intrinsic INT_PTR_KIND() which can be used in
        initialization expressions.  Users can store addresses in
        integer variables that are declared

                INTEGER(KIND=INT_PTR_KIND()) :: PTR

  This is just FYI for the committee.  Of course we should put
  something like this into Fortran 2000 since 64-bit machines are
  becoming more prevalent.  But it wasn't on the list of "modern"
  Fortran features.

  /Stan