Computing checksum for Ada newbie

Computing checksum for Ada newbie

[mop]

I've got two types - we'll call them TYPE_1, TYPE_2.

The checksum (last byte) for TYPE_1 is the byte eight.
The checksum (last byte) for TYPE_2 varies (depends on user parameters)  but
the threshold is byte 517.
The checksum is a simple sum of the the bytes (dont care about overflow)
An example of TYPE_1 is provided.  "BYTE" is defined in my package.

type TYPE_1 is
record
 XX             :  BYTE;  -- first byte
 YY             :  BYTE;  -- second byte
-- etc
 Checksum  :  BYTE;  -- eighth byte
end record;

I want a function - we'll call it Compute_Checksum that'll sum the bytes

function Compute_Checksum return BYTE is  -- dont think this is right.  need
to pass in which type
   INTEGER : Checksum :=0;
begin
-- more help here
end Compute_Checksum;

Re: Computing checksum for Ada newbie

[tmoran]

Do you mean something like:

type BYTE is mod 256;  -- ignore overflow

type TYPE_1 is
record
 XX             :  BYTE;  -- first byte
 YY             :  BYTE;  -- second byte
 Third, Fourth, Fifth, Sixth, Seventh : BYTE;
 Checksum  :  BYTE;  -- eighth byte
end record;

function Compute_Checksum(X : in TYPE_1) return BYTE is
begin
  return X.Checksum;
end Compute_Checksum;

  or perhaps

function Compute_Checksum(X : in TYPE_1) return BYTE is
begin
  return X.XX+X.YY+X.Third+X.Fourth+X.Fifth+X.Sixth+X.Seventh;
end Compute_Checksum;

  or perhaps

procedure Compute_Checksum(X : in out TYPE_1) is
begin
  X.Checksum := X.XX+X.YY+X.Third+X.Fourth+X.Fifth+X.Sixth+X.Seventh;
end Compute_Checksum;

and similarly for TYPE_2, etc.

Re: Computing checksum for Ada newbie

[John McCabe]

On Tue, 28 Aug 2001 11:11:47 -0400, "mop"
<mop65715@pegasus.cc.ucf.edu> wrote:

>I've got two types - we'll call them TYPE_1, TYPE_2.
>
>The checksum (last byte) for TYPE_1 is the byte eight.
>The checksum (last byte) for TYPE_2 varies (depends on user parameters)  but
>the threshold is byte 517.
>The checksum is a simple sum of the the bytes (dont care about overflow)
>An example of TYPE_1 is provided.  "BYTE" is defined in my package.
>
>type TYPE_1 is
>record
> XX             :  BYTE;  -- first byte
> YY             :  BYTE;  -- second byte
>-- etc
> Checksum  :  BYTE;  -- eighth byte
>end record;
>
>I want a function - we'll call it Compute_Checksum that'll sum the bytes
>
>function Compute_Checksum return BYTE is  -- dont think this is right.  need
>to pass in which type
>   INTEGER : Checksum :=0;
>begin
>-- more help here
>end Compute_Checksum;
>
>

It's not 100% clear what you require here, but I would probably use
unchecked conversion of the record into a packed array of bytes then
calculate the checksum in a loop. Some people might consider this
cheating, but ... :-)


Best Regards
John McCabe