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From: Adam Beneschan <adam@irvine.com>
Newsgroups: comp.lang.ada
Subject: Re: Address and bit mask
Date: Tue, 30 Aug 2011 07:52:27 -0700 (PDT)
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On Aug 30, 3:34=A0am, Ludovic Brenta <ludo...@ludovic-brenta.org> wrote:

> If the extremely rare case where you really, really must do address
> arithmetic, you still don't need bitwise operations on addresses. =A0You
> simply use System.Storage_Elements like so:
>
> function Succ (A : in System.Address) return System.Address is
> =A0 =A0Alignment : constant Storage_Offset :=3D 2**3;
> =A0 =A0use System.Storage_Elements;
> begin
> =A0 =A0return (A + Alignment) mod Alignment;
> =A0 =A0-- note: "+" and "mod" are in System.Storage_Elements
> end Increment;

"mod" won't return a System.Address.  (Not to mention that you can't
end a function Succ with "end Increment", but now I'm just being
picky.)

Here's a function that rounds A up to the next multiple of Alignment
(the result could equal A):

 function Align_Up (A : in System.Address) return System.Address is
    Alignment : constant Storage_Offset :=3D 2**3;
    B : System.Address;
    use System.Storage_Elements;
 begin
    B :=3D A + (Alignment - 1);
    return B - (B mod Alignment);
      -- the latter has the effect of zeroing out the low bits of B,
like B & ~ALIGN_MASK
 end Align_Up;

                         -- Adam