Re: Curiosity about rage checking

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Thu, 7 Feb 2008 02:36:01 -0800 (PST), framefritti@gmail.com wrote:

> Jean-Pierre Rosen ha scritto:
> 
>> framefritti@gmail.com a �crit :
>>> [..]
>>>
>>> My question is: is an Ada compiler allowed to move the check outside
>>> the loop?
>>
>> This question is addressed in the (in)famous paragraph 11.6. If you
>> don't understand exactly what it says, don't worry, you are not alone...
>>
>> But the important issue is that compilers are unlikely to perform that
>> optimization. Why? Because optimization is a matter of improving what's
>> normally used. And any decent Ada programmer should write that loop as:
>>
>> for I in X'range loop...
>>
>> Where the optimization becomes trivial
> 
> I agree, and that is what I usually do, but there are times when you
> want to loop
> over a limited part of X or not in the usual order (e.g., transposing
> a matrix stored (for whatever
> reason) as a one-dimensional array)

You still can follow that path:

Assuming that X is array (Integer range <>) of something real (:-)):

   subtype Domain is Integer range X'Range;
   subtype Subdomain is Domain range Domain'First + 1..Domain'Last - 1;
begin
   for I in Subdomain loop
      X (I) := 0.0; -- The compiler should know that I is from X'Range
   end loop;

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de