Re: The right way to handle this difference in Ada

[Eric Jacoboni <jaco@neottia.net>]

"vic" <ppp@ppp.it> writes:

> type unsigned_int_12_type is range 0..(2*12)-1;

I guess you wanted to say:

type unsigned_int_12_type is range 0..(2**12)-1;
for unsigned_int_12_type'Size use 12;

> and these 2 variables of the above type:
>
> a: unsigned_int_12_type;
> b: unsigned_int_12_type;
>
> If the code must perform a difference between a and b, say:
>
> c := a-b
>
> 1) which should be the type of c? I think it should be something like:

C can be a unsigned_int_12_type, as (a - b) _is_ a unsigned_int_12_type
(at least, i guess). Of course, if b > a, execution will raise a
Constraint_Error...

But, as far i've understood, you want to allow situations where b > a ?

type Unsigned_Int_12_Type is mod 2**12;
for Unsigned_Int_12_Type'size use 12;

type Int_12_Type is -(2**11)..+(2**11) - 1;
for Int_12_Type'size use 12;

C : Int_12_Type;
A, B : Unsigned_Int_12_Type;

A := 10; B := 12;
C := Int_12_Type(A - B);  -- C = -2


> type signed_int_12_type is range -unsigned_int_12'last ..
> unsigned_int_12'last.

> Is this right?

No, if unsigned is 0..2^n - 1, signed should be -2^(n-1)..+2^(n-1) - 1


> 2) And I should rename a "-" operation which gets two signed_int_12_type  as
> operands and returns signed_int_12_type as result?

like this :

function "-"(A, B : in Unsigned_Int_12_Type) return Int_12_Type;


-- 
�ric Jacoboni, n� il y a 1393940281 secondes