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# [Frama-c-discuss] Problem with ACSL annotations

```Hello Patrick,

Bur my problem is not solved.
I tried to follow the max_element in the ACSL_By_example.
This is my new program annotated:

/*@ requires \valid_range(queue,0,n-1) && n>0;
??? assigns \nothing;

??? ensures \forall integer i; 0 <= i <= n-1 ==> \result >= queue[i];
??? ensures \exists integer e; 0 <= e <= n-1 && \result == queue[e];

*/
int find_array_max(int* queue, int n){

? int i, largest;

? largest = 0;
/*@ loop variant n - i;
??? loop invariant 0 <= i <= n;
?? loop invariant \forall integer k; 0 <= k < i ==> queue[k] <= largest ;
?? loop invariant \exists integer e; 0 <= e <= n-1 && largest == queue[e];

*/
? for (i = 0; i < n; i++) {
??? if (queue[i] > largest)
????? largest = queue[i];
? }

? return largest;

}

Could you, please, tell me why I am still not able to verify all the VC? The problem still in the " loop invariant \exists integer e; 0 <= e <= n-1 && largest == queue[e];".

Best regards,
Intissar

________________________________
De?: BAUDIN Patrick <Patrick.Baudin at cea.fr>
??: frama-c-discuss at lists.gforge.inria.fr
Envoy? le : Mercredi 19 d?cembre 2012 15h21
Objet?: Re: [Frama-c-discuss] Problem with ACSL annotations

Hello Initisar,

Yes, It is a good idea to look at ACSL tutorial recommended by Jens.

But, just looking at these two lines of your previous mail :
> This new version is verifiable:
> ensures \exists int e; 0<=e && (\forall int i; 0<=i<15 && e > queue[i]) && ( (e >= 5) || (e >= 10) ) ==> \result == 0;
I can see that you didn't fully understand the answer of Virgile.

That ensures is almost equivalent to:
ensures false ==> what_ever;
This is always true what ever does your code!

The ensures of your first mail is almost equivalent to
? ensures what_ever ==> false;
A function doing the impossible can be compliant with this specification.
That is difficult to implement!
An alternative is to implement a function which doesn't terminate (while(true);).
I guess your code is not like that.

So, in addition to the tutorial, look again more carefully at the answer of Virgile.

Patrick.

-- Patrick Baudin, DILS/LSL, B?t. 862,
Point Courrier n? 174
Institut CARNOT CEA LIST,
CEA Saclay Nano-INNOV,
91191 Gif-sur-Yvette cedex, France.
tel: +33 (0)1 6908 2072

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