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

["Randy Brukardt" <randy@rrsoftware.com>]

"Marius Amado-Alves" <marius@amado-alves.info> wrote in message
news:mailman.42.1153428092.30988.comp.lang.ada@ada-france.org...
> > Surely a record rep clause, and then simple usage of its
> > components, is more readable, and more likely to be correct, and  even
more
> > likely to generate optimized code, than source code littered with
complex
> > arithmetic expressions.
>
> Actually, in this case, no. Time needs an order relation. Implemented
> as a record you have to write the relation functions--and you can
> botch there.

True enough.

> Implemented as a modular type the predefined relation
> functions are gratis--and surely correct.

Only if you've carefully laid out the order of the bits so that will work.
Which is much more likely to ruin the alignment of the bit-field components
(an important part of maximum performance).

> And the expressions are not
> complex. Once you get the masks and magnitudes right, it's simply
>
> Part := (Whole and Mask) / Magnitude.

But that's for each component. Surely you do other operations (like
difference in seconds) where the expressions are  far more complex?

All-in-all, I prefer the record representation. (Case in point: the
Janus/Ada Calendar.Time implementation is a 64-bit record type.) But there
may be exceptions - and, in any case, if the type is properly encapsulated,
it's not that big of a deal either way (no one should be looking at the raw
representation of times no matter what they are).

                         Randy.