Re: Why should hackers love Ada. (Re: Ada 95 based RTOS)

[kilgallen@eisner.decus.org (Larry Kilgallen)]

In article <38B55928.8A0EAB06@quadruscorp.com>, "Marin D. Condic" <mcondic-nospam@quadruscorp.com> writes:
> Gary wrote:
>> I see this reference to ADA being good at bit twiddling, periodically.
>> Virtually all high-level languages provide facilities for bit twiddling.  Is
>> there something unique about ADA (I'm a non-ADA programmers, sorry).  Is this
>> a reference to a transfer function (other languages have this) or memory
>> aliasing tricks?
> 
> Well, I don't know what the rest of the world means by "bit twiddling"
> but I know what *I* mean when I say that. ;-)
> 
> You have all the facilities you need in Ada (Ada95 - Ada83 didn't do
> this well) to do shifting, masking & other manipulations of individual
> bits within words. If you've ever had to do interfacing to low level
> devices, hardware registers, I/O ports, etc., then you know that you
> can't always deal with data as an "abstraction" where you can allow the
> compiler to pick whatever representations it wants and manipulate things
> any way it likes. Often I have been up against time constraints where
> even if a high level method of solving the problem may work fine, we
> dipped into bit masks and logical operators because they degenerated to
> much more efficient code.
> 
> Ada95 lets you get at things like this when you need to. The difference
> between Ada and C on this issue is that with Ada it is a "last resort"
> whereas with C it is a "way of life". (Look at how lots of bindings to C
> stuff includes numeric constants for specifying options by or'ing
> together the constants. While Ada can do that, it isn't the usual
> idiom.)

I think a major advantage of Ada is that it lets the programmer deal
at a higher level for the main body of the program, while only the
interface description contains the specification that bits 2-4 are
treated as a numeric field for the unit number.  The compiler aids
and enforces adherence to that specification without requiring the
programmer to be constantly thinking about it and getting it right.