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From: gdemont@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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> 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 :-)

I'm not sure that Mr Binetti intends to do dirty things.

After all, the conversions like Character'Pos <-> modular
or signed <-> modular precisely draw the attention about
when you enter the realm of bit twiddling on a certain number
of bits, and when some bit and bit length have a special
meaning. They are verbose enough to be re-found after a while,
and to discourage using them when a "* (2**7)" or a "mod 32" suffices.
The dirty thing would be e.g. to allow bit twiddling on a signed
integer, and this is the cause of fast-rotting code in C or some
Pascals; fortunately Ada95 doesn't allow it and has an elegant and
efficient solution for that issue.

I'm sure the users are adult enough to find the most appropriate
formulations for _their_ problems after some weeks of Ada
programming; therefore hiding the availability of modular types
_is_ a disservice. If one tells them that the only solution to mask
bits is to write 20 lines of records definitions with representation
clauses, they won't use Ada at all, simply!

Gautier


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