bitwise operations in Ada95

bitwise operations in Ada95

[Vladimir Bednikov]

Hi all.

Is there a way of performing bitwise operations on basic
types, e.g, integers, floats etc as in the bitwise and '&' and
bitwise or '|' in c.

thanks in advance

Re: bitwise operations in Ada95

[tmoran]

> Is there a way of performing bitwise operations on basic
> types, e.g, integers, floats etc as in the bitwise and '&' and
> bitwise or '|' in c.
    In Ada you can do logical operations on arrays of booleans.
If space is a consideration you can use pragma pack.  If that is
the wrong abstraction, you do bitwise "and" and "or" on modular
types, and you can convert integers to and from modular types if
they have the same size and you don't get in trouble with the
sign bit.  This won't work in general for floating point types,
clearly, so there you would have to use Unchecked_Conversion to
and from a suitable modular type.  If you are trying to mask
the exponent or mantissa of a float, conversion to a suitable
record, and then use of elements of the record, would probably
be more appropriate.
   The general answer to "is there a way ... as in c" is yes,
though perhaps not at the same abstraction level.

Re: bitwise operations in Ada95

[Lutz Donnerhacke]

* Vladimir Bednikov wrote:
>Is there a way of performing bitwise operations on basic
>types, e.g, integers, floats etc as in the bitwise and '&' and
>bitwise or '|' in c.

On (packed) arrays of boolean as well as on boolean or modular types you may
use 'and', 'or', 'not' ...

If you like to play with bits on other types you have to create a (non
portable) view using Unchecked_Conversion or (portable) representation
clauses.

Re: bitwise operations in Ada95

[Aquaman]

My question would be for a way to do bit shifting operations (vs. & |)
so for example shift left and shift right for use in mathmatical mult and div
opperations

thanks for any info





lutz@iks-jena.de (Lutz Donnerhacke) wrote in message news:<slrn9lamp5.hr.lutz@taranis.iks-jena.de>...
> * Vladimir Bednikov wrote:
> >Is there a way of performing bitwise operations on basic
> >types, e.g, integers, floats etc as in the bitwise and '&' and
> >bitwise or '|' in c.

Re: bitwise operations in Ada95

[Jacob Sparre Andersen]

Aquaman:

> My question would be for a way to do bit shifting operations (vs. & |)
> so for example shift left and shift right for use in mathmatical mult and div
> opperations

"*2" and "/2" works fine for me for that purpose (on modular
types).

Using packed arrays of booleans "(Bit_Pattern
(Bit_Pattern'First + 1 .. Bit_Pattern'Last), 0)" and "(1,
Bit_Pattern (Bit_Pattern'First .. Bit_Pattern'Last - 1))"
could be used. But I would hide them in functions, and maybe
allow shifting by more than one bit at a time.

I am certain that all current Ada compilers will implement
the first of these two solutions "the optimal way". I am not
so certain about the second, but it could easily be checked.

Anyway. The abstract concept you actually want to implement
seems to be "*2" and "/2", so why not just use that.

Jacob
-- 
"The point is that I am now a perfectly safe penguin!"

Re: bitwise operations in Ada95

[Sune Falck]

"Aquaman" <Matthew.Waterman@Honeywell.com> wrote in message
news:192e1f87.0107180742.4e2e83df@posting.google.com...
> My question would be for a way to do bit shifting operations (vs. & |)
> so for example shift left and shift right for use in mathmatical mult and
div
> opperations
>
> thanks for any info

The standard package Interfaces contains the following shift and rotate
functions
for all defined modular types.

From the Ada 95 standard anexx B.2

package Interfaces is
  ...
  type Unsigned_n is mod 2**n;
   function Shift_Left  (Value : Unsigned_n; Amount : Natural) return
Unsigned_n;
  function Shift_Right (Value : Unsigned_n; Amount : Natural) return
Unsigned_n;
  function Shift_Right_Arithmetic (Value : Unsigned_n; Amount : Natural)
return Unsigned_n;
  function Rotate_Left  (Value : Unsigned_n; Amount : Natural) return
Unsigned_n;
  function Rotate_Right (Value : Unsigned_n; Amount : Natural) return
Unsigned_n;
 ...
end Interfaces;

Sune Falck

Re: bitwise operations in Ada95

[Jacob Sparre Andersen]

I wrote:

> Aquaman:
> 
> > My question would be for a way to do bit shifting operations (vs. & |)
> > so for example shift left and shift right for use in mathmatical mult and div
> > opperations
> 
> "*2" and "/2" works fine for me for that purpose (on modular
> types).

[...]

But, as Sune wrote, package Interfaces contains functions
that do the same job.

Jacob (slightly embarrassed)
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