B.2 The Package Interfaces
Package Interfaces is the parent of several library
packages that declare types and other entities useful for interfacing
to foreign languages. It also contains some implementation-defined types
that are useful across more than one language (in particular for interfacing
to assembly language).
Static Semantics
The library package
Interfaces has the following skeletal declaration:
package Interfaces
is
pragma Pure(Interfaces);
type Integer_n is range -2**(n-1) .. 2**(n-1) - 1; --2's complement
type Unsigned_n is mod 2**n;
function Shift_Left (Value : Unsigned_n; Amount : Natural)
return Unsigned_n;
function Shift_Right (Value : Unsigned_n; Amount : Natural)
return Unsigned_n;
function Shift_Right_Arithmetic (Value : Unsigned_n; Amount : Natural)
return Unsigned_n;
function Rotate_Left (Value : Unsigned_n; Amount : Natural)
return Unsigned_n;
function Rotate_Right (Value : Unsigned_n; Amount : Natural)
return Unsigned_n;
...
end Interfaces;
Implementation Requirements
An implementation shall
provide the following declarations in the visible part of package Interfaces:
Signed and modular integer types of n bits,
if supported by the target architecture, for each n that is at
least the size of a storage element and that is a factor of the word
size. The names of these types are of the form Integer_n for the
signed types, and Unsigned_n for the modular types;
For each
such modular type in Interfaces, shifting and rotating subprograms as
specified in the declaration of Interfaces above. These subprograms are
Intrinsic. They operate on a bit-by-bit basis, using the binary representation
of the value of the operands to yield a binary representation for the
result. The Amount parameter gives the number of bits by which to shift
or rotate. For shifting, zero bits are shifted in, except in the case
of Shift_Right_Arithmetic, where one bits are shifted in if Value is
at least half the modulus.
Floating point types corresponding to each floating
point format fully supported by the hardware.
Support for interfacing to any foreign language
is optional. However, an implementation shall not provide any attribute,
library unit, or pragma having the same name as an attribute, library
unit, or pragma (respectively) specified in the following clauses of
this Annex unless the provided construct is either as specified in those
clauses or is more limited in capability than that required by those
clauses. A program that attempts to use an unsupported capability of
this Annex shall either be identified by the implementation before run
time or shall raise an exception at run time.
Implementation Permissions
An implementation may provide implementation-defined
library units that are children of Interfaces, and may add declarations
to the visible part of Interfaces in addition to the ones defined above.
A child package of package Interfaces with the
name of a convention may be provided independently of whether the convention
is supported by the pragma Convention and vice versa. Such a child package
should contain any declarations that would be useful for interfacing
to the language (implementation) represented by the convention. Any declarations
useful for interfacing to any language on the given hardware architecture
should be provided directly in Interfaces.
Implementation Advice
This paragraph was
deleted.
An implementation supporting an interface to C, COBOL,
or Fortran should provide the corresponding package or packages described
in the following clauses.
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