Re: bit manipulation

[Matthew Heaney <matthew_heaney@acm.org>]

Jack Chow <jackchow@home.com> writes:

> Can anyone tell me how to do bit manipulation such as bitwise-and and
> bitwise or?

For modular types, of the form

  type T is mod 256;   -- or whatever modulus is req'd

then bitwise "and" and "or" are provided as primitive operations:

   O1, O2 : T;
begin
   O3 := O1 and O2;
   O4 := O2 or O3;


You can also do and'ing and or'ing of boolean arrays:

   type Bit_Array is array (Positive range 0 .. 7) of Boolean;

   for Bit_Array'Size use 8;
  
   pragma Pack (Bit_Array);



  O1, O2 : Bit_Array;
begin
  O3 := O1 and O2;
  O4 := O2 or O3;



Realize that there's often a higher-level way to accomplish a goal in
Ada than in C.  For example, you can declare a record and specify the
location of the components:

   type RT is
     record
       A : Integer range 0 .. 3;
       B : Integer range 0 .. 15;
       C : Integer range 0 .. 3;
     end record;

   for RT use
     record
       A at 0 range 0 .. 1;
       B at 0 range 2 .. 5;
       C at 0 range 6 .. 7;
     end record;

   for RT'Size use 8;



   O : RT;
begin
   O.A := 1;
   O.B := 2;
   O.C := 0;


No bit-level manipulation of the fields is required.

You can also use the bit-manipulation facilities in the package
Interfaces, described in Annex B of your RM.

There's an online RM at the Ada home.

<http://www.adahome.com/>