Re: Address and bit mask

[Adam Beneschan <adam@irvine.com>]

On Aug 30, 3:34 am, 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.  You
> simply use System.Storage_Elements like so:
>
> function Succ (A : in System.Address) return System.Address is
>    Alignment : constant Storage_Offset := 2**3;
>    use System.Storage_Elements;
> begin
>    return (A + Alignment) mod Alignment;
>    -- 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 := 2**3;
    B : System.Address;
    use System.Storage_Elements;
 begin
    B := 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