Re: Constrained or Unconstrained Arrays or just my my Ignorance.

[Adam Beneschan <adam@irvine.com>]

On Feb 27, 2:20 pm, adacrypt <austin.oby...@hotmail.com> wrote:
> In my Ada-95 driven crypto program I want to capture the frequency
> spread of the ciphertext.
>
> I am not sure if I am right or not in what I am doing – a ‘ploy’ I
> use  works under certain conditions and then not at all at other times
> in a different application.
>
> This is my method and the source code of my method.
>
> CipherText item := 4675432 (say)
>
> Q := CipherText;
> I_Num(Q) := I_Num(Q)+1;
>
> SUBTYPE Index_32 IS Integer RANGE MinValue  .. MaxValue;
> TYPE I_CoefficientsNumArray IS ARRAY(Index_32) OF Integer;
>  I_Num : I_CoefficientsNumArray;
> -- counts the coefficients of the ciphertext.
> -- Max Value and MinValue are the expected values of any ciphertext as
> positive integers
>
> *I use the value of the current ciphertext element to index the
> (subscript) corresponding numerically to the array  element where it
> will be stored and I later print out the contents of all the array
> elements to get the frequency spread of an entire encryption session..
>
> 1) Is this action legit in terms of Ada-95 Reference Manual?  I am not
> experienced enough to know myself.
>
> I suspect it might not be quite proper but it works fine!  I fear it
> might just be bug that is working more by good luck than good design
> by me - I hope this is kosher because I want to go on using it in the
> future.  It works as a procedure in a much larger program ok but does
> not work at all in a second case 2) below..
>
> 2) When I try using this in a standalone program i.e. as the sole
> purpose of a dedicated program that is meant to find the frequency
> spread of any file that is read in experimentally, it definitely does
> not work.
>
> Your advice would be greatly appreciated.

Did you initialize I_Num?  The way you declared it, the initial values
of the elements of I_Num could be anything.

I'm just guessing at what the problem might be.  The code looks fine
(I don't know what MinValue and MaxValue are, so if the difference
between them is very large, you could be creating a very large array.
If that's what you want, fine).  You don't give us any details about
what's going wrong except for "it definitely does not work".  So I'm
stabbing blindly here.

If the problem is that the I_Num values don't get initialized, change
your declaration to something like

  I_Num : I_CoefficientsNumArray := (others => 0);

which gives the array an initial value.

                     -- Adam