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From: sands@clipper.ens.fr (Duncan Sands)
Newsgroups: comp.lang.ada
Subject: Higher precision and generics
Date: 11 Mar 1995 17:41:03 GMT
Organization: Ecole Normale Superieure, PARIS, France
Distribution: world
Message-ID: <3jsnbf$ido@nef.ens.fr>
NNTP-Posting-Host: drakkar.ens.fr
Date: 1995-03-11T17:41:03+00:00
List-Id: <comp.lang.ada>

I am writing a package of matrix routines (in Ada!) in which some intermediate results
should be calculated in higher precision than normal.  The type for normal precision is
called Real and is a generic parameter of my package:
generic
   type Real is digits <>;
package Matrix_Stuff is
   ...
end;

In the body I would like to be able to declare Double to be a higher precision
floating point type, something like:
package body Matrix_Stuff is
   type Double is digits 2*Real'Digits;
   ...
end;

Unfortunately, this does not compile: apparently formal types like Real are not
considered static, so Real'Digits is not considered static, and only static
expressions are allowed in a "type X is digits expression" declaration.  (If
I write "type Double is digits 2*Float'Digits" then it compiles fine).

What can I do to get type Double to be of higher precision than Real?
Can anyone please help?  And does anyone know why formal types like Real are not
considered static?

Thanks a lot,

Duncan Sands.