Re: Problem trying to implement generics.

["Marin David Condic" <marin.condic.auntie.spam@pacemicro.com>]

Most of the conditions in which I've seen people doing bitwise operations
(shifts, xors, etc.) seem to be handled in Ada by proper use of
representation clauses. You create records that match the bit layout of
registers or packed arrays of boolean & similar things. Unless the Ada
implementation of access to these fields is pathetically slow, it usually is
going to handle things much more cleanly. Need a three bit integer from the
center of a machine word? Put it in a rep claused record and just use
assignment!

Still, its handy to have the logical operations. One really great use I had
for them was when reading/writing various A/D and Discrete values from
hardware. By always doing an XOR of the input with a constant in memory, you
could plug the constant at runtime with a monitor program and toggle the
input bits. This was invaluable for testing. (Same trick works with always
adding a constant to a mathematical input - "tuning" constants, as it were.)
So having logical operations is very useful in many spots. But I think
you're right about them being used to compensate for a lack of language
facilities in most cases.

MDC
--
Marin David Condic
Senior Software Engineer
Pace Micro Technology Americas    www.pacemicro.com
Enabling the digital revolution
e-Mail:    marin.condic@pacemicro.com
Web:      http://www.mcondic.com/


"Larry Kilgallen" <Kilgallen@eisner.decus.org.nospam> wrote in message
news:YlSyXUaQmD+$@eisner.encompasserve.org...
> In article <9bkfk4$6a2$1@nh.pace.co.uk>, "Marin David Condic"
<marin.condic.auntie.spam@pacemicro.com> writes:
>
> Thinking about device drivers I have written (not in C or Ada) it seems
> to me that bit shifting is most likely to be the "manual" operation used
> in low-level languages where the conceptually desired operation is not
> supported.
>
> For instance, if one has a numeric field that is supposed to be
> positioned three bits left in a register the low-level approach
> (at the source level) would be to "shift" and "or" it together
> with the other bits before setting it into the register.
>
> The conceptual operation is to store a field into a register-format
> record before setting it into a record.  The Ada method is much
> more logical, except for those with lots of experience writing
> drivers in lesser languages.