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 15:15:20 +0100
  • In-reply-to: <D952B9ACEBFA4A6A9BC0864D26FDE670@AHARDPLACE>
  • References: <D952B9ACEBFA4A6A9BC0864D26FDE670@AHARDPLACE>
Now I realized, that if I would use && instead of ==> for the \exists statement I get a green light.
But I have no Idea why, I would like to know the difference.

Cheers 
Christoph
  ----- Original Message ----- 
  From: Christoph Weber 
  To: frama-c-discuss at lists.gforge.inria.fr 
  Sent: Monday, December 15, 2008 3:09 PM
  Subject: [Frama-c-discuss] returns vs loop invariants


  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


------------------------------------------------------------------------------


  _______________________________________________
  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/20081215/aa33bb06/attachment-0001.htm