Bit operations in Ada (one's complements and sum)

Bit operations in Ada (one's complements and sum)

[ebresie]

I am curious if there exists either built in or already developed
somewhere, a bit manipulation package.

I am trying to have 16-bit numbers that are made into one's complement
and have one's complement summation occur with the values.

I started working on some of it, but thought I would check to see if
maybe this functionality already exists somewhere in ADA95 or exists
somewhere (one of the things about ADA is reusablility right :-)

I am not an expert of package development so any help would be
appreciated.

I started thinking that I would have something along the lines of:

package Bits is

-- I was thinking of using an array of Booleans but wasn't sure if this
-- was the most efficient way of working with Bits.
   type BIT_String is new String;
   type Ones_Complement is new BIT_String;
   type Twos_Complement is new BIT_String;

   function Ones_Complement( N : Integer ) return BIT_String;
   function Twos_Complement( N : Integer ) return BIT_String;
   function "+"( Left: Ones_Complement; Right : Twos_Complement ) return
Ones_Complement;
   function "+"( Left: Twos_Complement; Right : Twos_Complement ) return
Twos_Complement;

end Bits

The implementation I haven't completed yet...but figured I would check
with you guys first.

The implementation basically would take the Integer, check for negative
value, store a 1 for negative/0 for postive, then div/mod by two to get
each bit place.

I guess I should be able to somehow make this seperate from the
data type Integer and make it more abstract...how is the best way to do
that?

I am I just making this harder then I need to?

Any help would be appreciated

Eric Bresie
ebresie@usa.net


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Re: Bit operations in Ada (one's complements and sum)

[Ted Dennison]

ebresie@usa.net wrote:

> I am curious if there exists either built in or already developed
> somewhere, a bit manipulation package.
>
> I am trying to have 16-bit numbers that are made into one's complement
> and have one's complement summation occur with the values.

One's complement is just a "not" operation. You won't find a package to do
that, because it is too trivial of an operation for someone to make an
entire package out of. You just use the "not" operator on a packed array of
booleans or on a modular integer.

Some examples of this for unpacked arrays of boolean (aka: "Sets") are up on
AdaPower at http://www.adapower.com/lang/sets.html . But if you would like
to perform math operations on the same data without converting it, modular
integers would probably be better for you.

--
T.E.D.

Home - mailto:dennison@telepath.com  Work - mailto:dennison@ssd.fsi.com
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Epistemology [was: Bit operations in Ada (one's complements and sum)]

[Nick Roberts]

First, I wonder if Eric was talking about ones-complement arithmetic with
carry? If so, then (I think!) standard Ada doesn't have such an operation
explicitly built-in.

Second, forgive my musing on this subject, but it did just flicker across my
mind, that a 'bit string' is indeed a kind of string, but ... it's also a
set, but ... it's also an integer, but ... it's also a JPEG picture, but ...
well, you get the idea. Things are not what they are, are they? Just a
thought.

BTW probably "type Bit_String is private;" in the package spec.

--
Nick Roberts
http://www.AdaOS.org

Re: Epistemology [was: Bit operations in Ada (one's complements and sum)]

[Robert Dewar]

In article <8pchk8$co01k$1@ID-25716.news.cis.dfn.de>,
  "Nick Roberts" <nickroberts@callnetuk.com> wrote:
> Second, forgive my musing on this subject, but it did just
> flicker across my mind, that a 'bit string' is indeed a kind
> of string, but ... it's also a set, but ... it's also an
> integer, but ... it's also a JPEG picture, but ... well, you
> get the idea. Things are not what they are, are they? Just a
> thought.

Sounds like you have rediscovered the fundamental and important
distinction between storage structures and data structures :-)


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