Frama-C-discuss mailing list archives

This page gathers the archives of the old Frama-C-discuss archives, that was hosted by Inria's gforge before its demise at the end of 2020. To search for mails newer than September 2020, please visit the page of the new mailing list on Renater.


[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[Frama-c-discuss] Problem with ACSL annotations



Hello Patrick,

Thank you for your answer.
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];".

Thanks in advance.

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.
That should help you in understanding why your specification is equivalent to what I say.

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


_______________________________________________
Frama-c-discuss mailing list
Frama-c-discuss at lists.gforge.inria.fr
http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/frama-c-discuss
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.gforge.inria.fr/pipermail/frama-c-discuss/attachments/20121221/6aa9ce58/attachment.html>