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# [Frama-c-discuss] Problem with loop invariant

• Subject: [Frama-c-discuss] Problem with loop invariant
• From: Claude.Marche at inria.fr (Claude Marche)
• Date: Mon, 21 Jun 2010 11:03:49 +0200
• References: <1276795121.1681.16.camel@iti27>

```Boris Hollas wrote:
> Hello,
>
> in the loop below, both assertion can be verified, but not the loop
> invariant. The assertions are the same as the 3rd loop invariant that
> can't be proved. Since the assertion holds (as proved by Jessie) both at
> the beginning and at the end of the loop body, I don't understand why
> the loop invariant can't be proved.
>
I guess it is because

internal.msgnum++

is executed between the second assert and the loop invariant
preservation checking

- Claude
> I should have used integer instead of int in the specification, btw.
>
> /*@
> 	loop variant MSGCOUNT - internal.msgnum;
> 	loop invariant 0 <= internal.msgnum &&
> 		\forall int x; 0 <= x < internal.msgnum ==>
> 	*/
> for (internal.msgnum = 0;internal.msgnum < MSGCOUNT; internal.msgnum++)
> {
> 	//@ assert \forall int x; 0 <= x < internal.msgnum ==>
> 	//@ assert \forall int x; 0 <= x < internal.msgnum ==>
> }
>
>
>

--
Claude March?                          | tel: +33 1 72 92 59 69
INRIA Saclay - ?le-de-France           | mobile: +33 6 33 14 57 93
Parc Orsay Universit?                  | fax: +33 1 74 85 42 29
4, rue Jacques Monod - B?timent N      | http://www.lri.fr/~marche/
F-91893 ORSAY Cedex                    |

```