Re: Interfaces.Shift_Left

[Simon Wright <simon@pushface.org>]

awdorrin <awdorrin@gmail.com> writes:

> Cur_Word := (Cur_Word OR Shift_Left( Unsigned_32(Data),
> Bits_To_Shift));
> INT_PTR.all := Integer_32(Cur_Word);
>
> I understand that the result from the shift_left is a negative number,
> so it is being seen by Ada as a large positive number ( > (2^31-1))
> which is why I'm getting the Constraint error;
>
> Maybe its my history with C that is confusing me, but shouldn't there
> be an easy way to cast the value back to a negative Integer_32 from an
> Unsigned_32?

Ada doesn't have an easy way to do what you ask; one way you can do it
is by instantiating Ada.Unchecked_Conversion, which is deliberately
obvious so that reviewers know that they have to take more care than
usual.

It'd be much easier if Data was Unsigned_32 to start with, and if
instead of INT_PTR you had an Unsigned_32_Ptr.