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From: Robert Dewar <robert_dewar@my-deja.com>
Subject: Re: Bit manipulation
Date: 2000/11/08
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Date: 2000-11-08T00:00:00+00:00
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In article <8ub6kt$6nd$1@nnrp1.deja.com>,
  gdemont@my-deja.com wrote:
> But:
>  "Which way may I shift bits, or mask them?"
>
> And your hint about using records, arrays and representation
> clauses is completely overkill just for blipping bits! Please
> give constructive answers!

Nope! When someone asks how can I do "xxx" and xxx is a low
level implementation technique, it is always appropriate to
enquire as to what the problem is.

A C programmer is used to shifting and masking as a solution
for all sorts of problems. Now there are cases where such
a solution is appropriate in Ada, which is why the capability
was added in Ada 95, but compared to C, they are few and
far between.

Clearly the underlying question is "how do I do shifts and
masks to achieve xxx", and to accurately answer this question
we need to ask what xxx is. Quite likely the answer will
be "don't use shifts and masks to achieve xxx if you are
writing Ada, instead use yyy".

Of course we could give a simple answer involving the
obvious solution of converting Character'Pos values to
a modular type and then doing shifts and masks in the
normal manner, but that would be a disservice.

I see a *lot* of code that is clearly written by C programmers
and greatly overuses low level bit twiddling techniques that
are appropriate to C but not to Ada.

If someone simply wants to get a job done in the dirtiest
possible fashion, and wants someone else to do the work,
CLA is not the place to expect free help :-)


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