Re: Newbie question : types , representation

[Martin Dowie <martin@dowie-cs.demon.co.uk>]

there is a predefined package in Ada95 called 'Interfaces' which defines
modular types and a whole heap of operations to manipulate them as you
require.

try following this link -

http://www.adahome.com/rm95/rm9x-B-02.html#3

Jos De Laender wrote:

> Hi,
>
> I'm trying to learn ADA on my own.
>
> My background is C programming (sorry ;-) ) and VHDL hardware
> programming. The latter helps a lot , as VHDL inherited a lot of ADA.
>
> I'm having trouble with following very simple problem , at least in
> doing it portable and clean.
>
> In base64 decoding , each ASCII character must be translated to 6 'bit'.
> 4 characters translate then to 3 bytes. The problem and algorithms are
> trivial. In C I could do it within 5 minutes.
>
> It would involve some bitmanipulation (shifting , anding , oring ) on
> the character itself and then outputting. That's it.
>
> However, what's unclear is how to do this in ADA types : A character
> cannot be bit manipulated , and so needs some explicit translation to a
> 'byte' or something.
> How is this usually done ? I would guess to use a modular type 2**8 ? If
> I declare such a type , and I want a byte , is this guaranteed by 2**8
> or do I have explicitly  to attribute it with a 'for Byte'size use 8' ?
> Also I will need some kind of assignment to that modular type, say aVar
> := 2#00000011#. This will assign the value 3 to aVar ? Is this
> guaranteed to have that bit pattern ? Or could I imagine a (probably
> exotic) machine on which 3 is represented with another bit pattern ?
> Does ADA guarantee ?
> If I output aVar with a write function , is the bitpattern guaranteed ?
>
> Thanks for all clarifications.
>
> Jos