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From: Brooks Moses <bmoses-nospam@cits1.stanford.edu>
Newsgroups: comp.lang.ada,comp.lang.fortran
Subject: Re: Bounds Check Overhead
Date: Thu, 25 May 2006 15:27:33 -0700
Organization: Stanford University
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Xref: g2news2.google.com comp.lang.ada:4476 comp.lang.fortran:10260
Date: 2006-05-25T15:27:33-07:00
List-Id: <comp.lang.ada>

Simon Wright wrote:
> In Ada one should where possible use the 'Range attribute:
> 
>    for I in Some_Array'Range loop
>       Process (Some_Array (I));
>    end loop;
> 
> where I _can't_ exceeed the bounds, so it would be surprising if a
> compiler inserted bounds checks. Is there a Fortran equivalent? I seem
> to remember something like that in VAX F77, but it's been a while...

The Fortran equivalent is:

     do i = lbound(Some_Array), ubound(Some_Array)
       call Process(Some_Array(i))
     end do

I don't know that compilers are smart enough to omit the range check, 
though -- because, in the general case, it shouldn't be omitted.  There 
could be something in the body of the loop that modified the loop 
variable -- which would be illegal code, but the whole point of 
range-checking is that it works even if the code is illegal, so unless 
the compiler is otherwise able to guarantee that the loop variable is 
not modified by a statement in the loop, it still needs to do the check.

- Brooks


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