Annotated Ada Reference Manual — Legal Information

B.5 Interfacing with Fortran

1/3

{AI05-0229-1} The facilities relevant to interfacing with the Fortran language are the package Interfaces.Fortran and support for specifying the Import, Export and Convention aspect pragmas with convention_identifier Fortran.

The package Interfaces.Fortran defines Ada types whose representations are identical to the default representations of the Fortran intrinsic types Integer, Real, Double Precision, Complex, Logical, and Character in a supported Fortran implementation. These Ada types can therefore be used to pass objects between Ada and Fortran programs.

Static Semantics

The library package Interfaces.Fortran has the following declaration:

with Ada.Numerics.Generic_Complex_Types; -- see G.1.1
pragma Elaborate_All(Ada.Numerics.Generic_Complex_Types);
package Interfaces.Fortran is
pragma Pure(Fortran);

type Fortran_Integer is range implementation-defined;

type Real is digits implementation-defined;
type Double_Precision is digits implementation-defined;

type Logical is new Boolean;

package Single_Precision_Complex_Types is
new Ada.Numerics.Generic_Complex_Types (Real);

type Complex is new Single_Precision_Complex_Types.Complex;

   subtype Imaginary is Single_Precision_Complex_Types.Imaginary;
   i : Imaginary renames Single_Precision_Complex_Types.i;
   j : Imaginary renames Single_Precision_Complex_Types.j;

type Character_Set is implementation-defined character type;

12/3

{AI05-0229-1}    type Fortran_Character is array (Positive range <>) of Character_Set
      with Pack;
   pragma Pack (Fortran_Character);

function To_Fortran (Item : in Character) return Character_Set;
function To_Ada (Item : in Character_Set) return Character;

function To_Fortran (Item : in String) return Fortran_Character;
function To_Ada (Item : in Fortran_Character) return String;

   procedure To_Fortran (Item       : in String;
                         Target     : out Fortran_Character;
                         Last       : out Natural);

   procedure To_Ada (Item     : in Fortran_Character;
                     Target   : out String;
                     Last     : out Natural);

end Interfaces.Fortran;

17.a.1/1

Implementation defined: The types Fortran_Integer, Real, Double_Precision, and Character_Set in Interfaces.Fortran.

17.a

Ramification: The means by which the Complex type is provided in Interfaces.Fortran creates a dependence of Interfaces.Fortran on Numerics.Generic_Complex_Types (see G.1.1). This dependence is intentional and unavoidable, if the Fortran-compatible Complex type is to be useful in Ada code without duplicating facilities defined elsewhere.

The types Fortran_Integer, Real, Double_Precision, Logical, Complex, and Fortran_Character are Fortran-compatible.

The To_Fortran and To_Ada functions map between the Ada type Character and the Fortran type Character_Set, and also between the Ada type String and the Fortran type Fortran_Character. The To_Fortran and To_Ada procedures have analogous effects to the string conversion subprograms found in Interfaces.COBOL.

Implementation Requirements

20/3

{AI05-0229-1} An implementation shall support specifying aspect pragma Convention with a Fortran convention_identifier for a Fortran-eligible type (see B.1).

Implementation Permissions

An implementation may add additional declarations to the Fortran interface packages. For example, the Fortran interface package for an implementation of Fortran 77 (ANSI X3.9-1978) that defines types like Integer*n, Real*n, Logical*n, and Complex*n may contain the declarations of types named Integer_Star_n, Real_Star_n, Logical_Star_n, and Complex_Star_n. (This convention should not apply to Character*n, for which the Ada analog is the constrained array subtype Fortran_Character (1..n).) Similarly, the Fortran interface package for an implementation of Fortran 90 that provides multiple kinds of intrinsic types, e.g. Integer (Kind=n), Real (Kind=n), Logical (Kind=n), Complex (Kind=n), and Character (Kind=n), may contain the declarations of types with the recommended names Integer_Kind_n, Real_Kind_n, Logical_Kind_n, Complex_Kind_n, and Character_Kind_n.

21.a

Discussion: Implementations may add auxiliary declarations as needed to assist in the declarations of additional Fortran-compatible types. For example, if a double precision complex type is defined, then Numerics.Generic_Complex_Types may be instantiated for the double precision type. Similarly, if a wide character type is defined to match a Fortran 90 wide character type (accessible in Fortran 90 with the Kind modifier), then an auxiliary character set may be declared to serve as its component type.

Implementation Advice

An Ada implementation should support the following interface correspondences between Ada and Fortran:

An Ada procedure corresponds to a Fortran subroutine.

An Ada function corresponds to a Fortran function.

An Ada parameter of an elementary, array, or record type T is passed as a T_F argument to a Fortran procedure, where T_F is the Fortran type corresponding to the Ada type T, and where the INTENT attribute of the corresponding dummy argument matches the Ada formal parameter mode; the Fortran implementation's parameter passing conventions are used. For elementary types, a local copy is used if necessary to ensure by-copy semantics.

An Ada parameter of an access-to-subprogram type is passed as a reference to a Fortran procedure whose interface corresponds to the designated subprogram's specification.

26.a/2

Implementation Advice: If Fortran interfacing is supported, the interface correspondences between Ada and Fortran should be supported.

NOTES

18 An object of a Fortran-compatible record type, declared in a library package or subprogram, can correspond to a Fortran common block; the type also corresponds to a Fortran “derived type”.

Examples

Example of Interfaces.Fortran:

with Interfaces.Fortran;
use Interfaces.Fortran;
procedure Ada_Application is

30/3

{AI05-0229-1}    type Fortran_Matrix is array (Integer range <>,
                                 Integer range <>) of Double_Precision
      with Convention => Fortran;              ;
   pragma Convention (Fortran, Fortran_Matrix);    -- stored in Fortran's
                                                   -- column-major order
   procedure Invert (Rank : in Fortran_Integer; X : in out Fortran_Matrix)
      with Import => True, Convention => Fortran;;
   pragma Import (Fortran, Invert);               -- a Fortran subroutine

Rank : constant Fortran_Integer := 100;
My_Matrix : Fortran_Matrix (1 .. Rank, 1 .. Rank);

begin

   ...
   My_Matrix := ...;
   ...
   Invert (Rank, My_Matrix);
   ...

end Ada_Application;

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