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[Frama-c-discuss] WP plugin report incorrect

Well, the post-condition would follow from the loop invariant, if the
other loop invariant  start <= i < end was given.

In any case, the loop invariant is not preserved, its preservation
should not be reported to hold by WP.

I checked with Jessie, the loop invariant is not proved to be preserved.

By the way, Christoph, are you sure your file contains nothing else than
what you sent in your first mail? Because if there is something
inconsistent in the context, then everything will be reported as valid
by the provers.

- Claude

Le 05/10/2015 17:32, Loïc Correnson a écrit :
> Your function *is* doing something, and the post-condition is exactly your loop invariant with (i == end), hence it finally holds.
> 	L.
> 
> 
>> Le 5 oct. 2015 à 17:19, Christoph Rauch <christoph.rauch at fau.de> a écrit :
>>
>>
>>> On 05 Oct 2015, at 16:54, Loïc Correnson <loic.correnson at cea.fr> wrote:
>>>
>>> Yes ! Indeed, there is nothing about the preservation of the elements in the array across the function.
>>> Something like :
>>> /*@ …
>>> ensures
>>>    \forall integer i ; start <= i < end ==> 
>>>    \exists integer j ; start <= j < end ==> a[i] == \old( a[j] ) ;
>>> */
>>> (and the other way).
>>
>> Of course, that is a post-condition that should *also* hold in the final algorithm, and indeed I have formulated this using the Permut predicate from the Jessie tutorial. I only left it out here, because it didn’t change the result and it shouldn’t be a necessary condition. After all, the contract I gave would be fulfilled by a function that sets a[end-1] to INT_MAX. But doing nothing is not such a function and WP shouldn’t be able to prove that the post-condition holds.
>>
>> --
>> Christoph
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> 
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-- 
Claude Marché                          | tel: +33 1 69 15 66 08
INRIA Saclay - ÃŽle-de-France           |
Université Paris-sud, Bat. 650         | http://www.lri.fr/~marche/
F-91405 ORSAY Cedex                    |