Re: How do I use ADA to calculate a checksum?

["David C. Hoos, Sr." <david.c.hoos.sr@ada95.com>]

Hi Charles,

For what it's worth, here's how I would go about it, given the
limited "requirements specification.":

-- First, define a type for the checksum.
type Checksum_Type is <implementation-defined>;
-- Perhaps if you're looking for an n-bit checksum, the type would
-- be mod 2 ** N. (See the  LRM about modular types)


-- Next, define the checksum function specification:

function Checksum
   (Starting_Address : System.Address;
    Data_Length : Natural
   ) return Checksum_Type;

-- Now, we can define the function body:

function Checksum
   (Starting_Address : System.Address;
    Data_Length : Natural
   ) return Checksum_Type is
   -- Define a "storage unit" type
   type Storage_Unit_Type is mod 2 ** System.Storage_Unit;
   -- Define the type of an array of these "storage units"
   type Storage_Unit_Array_Type is array (1 .. Data_Length) of
Storage_Unit_Type;
   -- Define the array of data to be checksummed
   Storage_Unit_Array : Storage_Unit_Array_Type;
   -- Now, locate the array where the data is
   for Storage_Unit_Array'Address use Starting_Address;
  -- Define the object to be returned, initialized to zero
  The_Checksum : Checksum_Type := 0;
begin
   -- Now, the storage elements can be accessed individually -- e.g.,
   -- Note that this loop will be executed Data_Length times,
   -- even if Dat_Length is 0
   for i in Storage_Unit_Array'range loop
      --....:=... Storage_Unit_Array (i) .........
   end loop;
   -- ..........
   return The_Checksum;
end Checksum;

There are many good books on Ada95, and I own well over a dozen.  But.. if
I had
to limit myself to one it would be Norman Cohen's "Ada as a Second
Language",
Second Edition.  You can get it at Madison Books and Computers.

David C. Hoos, Sr.,
david.c.hoos.sr@ada95.com
(205) 726-4965

Charles Phillips <charles@scarecrow.gcs.redstone.army.mil> wrote in article
<3427DF0F.4467@scarecrow.gcs.redstone.army.mil>...
> Hello,
> 
> I'm relatively new to ADA95, and would like to ask for assistance
> from those of you who are more knowledgeable.
> 
> I have an embedded application which requires me to perform several
> checksum calculations.  The question is, when passed a starting 
> address and a length, how do I "increment" the address and then
> access the data at the location?
> 
> Any help or recommendations with respect to reference books would
> be greatly appreciated.
> 
> Charles
>