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From: Vinzent Hoefler <ada.rocks@jlfencey.com>
Newsgroups: comp.lang.ada
Subject: Re: Optimizing Boundary Checks
Date: Fri, 13 Jun 2003 14:38:33 +0200
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Date: 2003-06-13T14:38:33+02:00
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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:
>>=20
>>    type Index_Range is range 1 .. 10;
>>    type Items is array (Index_Range) of Natural;
>>=20
>> But if you write:
>>=20
>>    type Items is array (1 .. 10) of Natural;
>>=20
>> 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.

Well, the compiler *could* see that the type Index_Range always
satisfies the same constraint as for the array. I don't know for sure,
but I'd think, it does, because somehow it must store the constraints
for any type anyway and I strongly doubt that an optimizer would work
on type names instead of actual numbers describing their constraints.

OTOH, I think, using such unnamed indices is a quite bad idea anyway,
because it breaks the type safety. So simply: Don't do it. :-)


Vinzent.

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