guideline

Use modular types rather than Boolean arrays when you create data structures that need bit-wise operations, such as and and or.

with Interfaces;
procedure Main is
   type Unsigned_Byte is mod 255;

   X : Unsigned_Byte;
   Y : Unsigned_Byte;
   Z : Unsigned_Byte;
   X1 : Interfaces.Unsigned_16;
begin -- Main
   Z := X or Y;  -- does not cause overflow
show example of left shift
   X1 := 16#FFFF#;
   for Counter in 1 .. 16 loop
      X1 := Interfaces.Shift_Left (Value => X1, Amount => 1);
   end loop;
end Main;

rationale