Re: How do you bitwise operations in Ada '83 and '95

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Thu, 20 Jul 2006 05:03:23 -0400, Stephen Leake wrote:

> Marius Amado-Alves <marius@amado-alves.info> writes:
> 
>> Note that I don't do bit shifting. Instead I multiply or divide by a
>> magnitude. I don't think bit shifting is portable.
> 
> See LRM B.2, Interfaces.Shift_Left, Shift_Right, Rotate_Left, Rotate_Right.

Hmm, it reads (Ada 95):

"{shift} {rotate} 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."

That looks non-portable to me.

Here is my definition of "portable":

Let T is a modular type Unsigned_n compiled on two different machines. For
any valid X of T the result of Shift_Left (X, m) yields same numerical
value on both machines.

I don't know if that was overlooked or that was an intent of language
designers to get at the underlying machine representation. Probably the
latter. I'm not a language lawyer, though.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de