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From: "Tom LINDEN" <tom@kednos.com>
Newsgroups: comp.lang.ada,comp.lang.fortran,comp.lang.pl1
Subject: Re: Bounds Check Overhead
Date: Sat, 27 May 2006 10:52:03 -0700
Organization: Kednos
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Date: 2006-05-27T10:52:03-07:00
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WHY NOT STOP CROSS POSTING TO COMP.LANG.PL1, PLEASE?


On Sat, 27 May 2006 08:59:42 -0700, Dmitry A. Kazakov  =

<mailbox@dmitry-kazakov.de> wrote:

> On Sat, 27 May 2006 16:56:58 +0200, Ludovic Brenta wrote:
>
>> "robin" writes:
>>> "Simon Wright" writes:
>>>> In Ada one should where possible use the 'Range attribute:
>>>
>>> Ideally yes, but in practice, such as in sorting and averaging,
>>> the loop is often one or two short of the number of elements in the =
 =

>>> array.
>>
>> No problem:
>>
>> type Some_Array_Type is array (Positive range <>) of Something;
>>
>> procedure Walk (A : in Some_Array_Type) is
>> begin
>>    for J in A'First .. A'Last - 1 loop
>>       ...
>>    end loop;
>> end Walk;
>
> I don't think it is same. A range expression of A'First and A'Last is =
not
> statically required to be a subrange of A'Range (or maybe empty). So t=
he
> compiler had to prove that, if it would wish to omit checks. In your
> example it is trivially provable (if nobody had played with "-"), thou=
gh  =

> I
> am not sure if, say, GNAT really does it.
>
> Somebody had mentioned OCaml, I really doubt that inference is the  =

> answer.
> The programmer knows far more than the compiler (or pier viewer) could=

> infer. If J has to be in A'Range, I prefer that it could be specified
> rather than deduced.
>



-- =

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