Generic child unit renaiming

[noiraud@cenaath.cena.dgac.fr]

I would like to rename Math_Extension an extension of the
generic package Ada.Numerics.Generic_Elementary_Functions.

Thus, I created a generic child unit :

   generic
   package Ada.Numerics.Generic_Elementary_Functions.Extensions is

      function Log10 (X : Float_Type'Base) return Float_Type'Base;

      function Asin  (X : Float_Type'Base) return Float_Type'Base
         renames Arcsin;

   end Ada.Numerics.Generic_Elementary_Functions.Extensions;

and I tried the following renaming :

   with Ada.Numerics.Generic_Elementary_Functions.Extensions;

   generic package Math_Extension renames
      Ada.Numerics.Generic_Elementary_Functions.Extensions;

The GNAT compiler refused it :

   >>> invalid prefix in selected component "Generic_Elementary_Functions".

I read that a child of a generic parent can only be renamed if the renaming
occurs inside the declarative region of its parent unit, but I can't do it
because Generic_Elementary_Functions belongs to the predefined library.

An other solution could be to implement in Math_Extension package using an
instanciation of Generic_Elementary_Functions :

   generic
      type Real is digits <>;
   package Math_Extension is

      package Math is new Ada.Numerics.Generic_Elementary_Functions (Real);

      function Sqrt (X : Real'Base) return Real'Base renames Math.Sqrt;

      ...

      function Log10 (X : Real'Base) return Real'Base;

      function Asin  (X : Real'Base) return Real'Base
         renames Math.Arcsin;

   end Math_Extension;

but instanciate Math_Extension has a performance cost because of the double
instanciation.

Could anyone help me ?

Thanks in advance.