Re: Optimizing Boundary Checks

[Preben Randhol <randhol+abuse@pvv.org>]

Preben Randhol wrote:
> Erlo Haugen wrote:
>> On Fri, 13 Jun 2003 11:49:03 +0000 (UTC)
>> Preben Randhol <randhol+abuse@pvv.org> wrote:
>> 
>>> After reading some posts here lately I have understood that the compiler
>>> can optimise out boundary checks on say arrays if you do this:
>>> 
>>>    type Index_Range is range 1 .. 10;
>>>    type Items is array (Index_Range) of Natural;
>>> 
>>> But if you write:
>>> 
>>>    type Items is array (1 .. 10) of Natural;
>>> 
>>> is boundary checks then on?
>> 
>> Yes, but in this case (principally) every acces to the array has to be
>> checked, whereas in the former case, the index is guaranteed to be
>> within range.
> 
> I see. This is because the boundary checks are on the Index_Range type
> and thus one do not need them on Items too.
> 
> How is it if Index_Range was defined as a subtype of Integer?

Reason for asking is that I get:

t.adb:10:11: warning: value not in range of subtype of "Standard.integer" defined at line 6
t.adb:10:11: warning: "constraint_error" will be raised at run time

if I do:

   type Items is array (1 .. 10) of Natural;
   Boxes : Items;

begin
   
   Boxes(11) := 1;


-- 
Preben Randhol                    http://www.pvv.org/~randhol/