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B.5 Interfacing with Fortran

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The facilities relevant to interfacing with the Fortran language are the package Interfaces.Fortran and support for the Import, Export and Convention pragmas with convention_identifier Fortran.

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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

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The library package Interfaces.Fortran has the following declaration:

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     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);

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        type Fortran_Integer is range implementation−defined;

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

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        type Logical is new Boolean;

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

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        type Complex is new Single_Precision_Complex_Types.Complex;

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

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        type Character_Set is implementation−defined character type;

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        type Fortran_Character is array (Positive range <>) of Character_Set;
        pragma Pack (Fortran_Character);

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

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

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

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

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     end Interfaces.Fortran;

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

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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

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An implementation shall support pragma Convention with a Fortran convention_identifier for a Fortran−eligible type (see B.1).

Implementation Permissions

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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.

Implementation Advice

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

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     NOTES

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16  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

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Example of Interfaces.Fortran:

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

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        type Fortran_Matrix is array (Integer range <>,
                                      Integer range <>) of Double_Precision;
        pragma Convention (Fortran, Fortran_Matrix);    −− stored in Fortran's
                                                        −− column−major order
        procedure Invert (Rank in Fortran_Integer; in out Fortran_Matrix);
        pragma Import (Fortran, Invert);                −− Fortran subroutine

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

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     begin

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

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     end Ada_Application;