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] returns vs loop invariants

  • Subject: [Frama-c-discuss] returns vs loop invariants
  • From: Christoph.Weber at first.fraunhofer.de (Christoph Weber)
  • Date: Mon, 15 Dec 2008 15:09:08 +0100
Hello,

thanks a lot for the help.

The problem with this algorithms is caused in the behavior not_equal

I think it is due to the implication

ensures (\exists integer i; 0 <= i < length ==> \old(a[i]) != \old(b[i])) ==> \result == 0;

I think the "exists..." cannot be proven.
If I would reverse the implication its fine.

I thought about a returns- statement in the loop, but I have no idea how to use it or if it would work.

I would appreciate any help to solve this problem.

Besides, I havew realized, that if I would  parenthesize "\result == 1" Jessie would not list it at all. 

I use Lithium.

/*@
requires 0 <= length;
requires \valid_range (a, 0, length);
requires \valid_range (b, 0, length);

assigns \nothing;
behavior equal:
ensures \result == 1 <==> (\forall integer i; 0 <= i < length ==> \old(a[i]) == \old(b[i]));
behavior not_equal:
ensures \result == 0 <==> (\exists integer i; 0 <= i < length ==> \old(a[i]) != \old(b[i]));
*/
int equal_array (int* a, int length, int* b )
{
int index_a = 0;
int index_b = 0;
/*@
loop invariant 0 <= index_a <= length;
loop invariant 0 <= index_b <= length;
loop invariant index_a == index_b;
loop invariant \forall integer k; 0 <= k < index_a ==> \at(a[k],Pre) == \at(b[k],Pre);

*/
while ( index_a != length )
{

if (a[index_a] != b[index_b])
return 0;
++index_a;
++index_b;

}
return 1;
}

Cheers 

Christoph
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.gforge.inria.fr/pipermail/frama-c-discuss/attachments/20081215/cad2c01b/attachment.htm