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[Frama-c-discuss] Using a identifier in an "assumes" clause

  • Subject: [Frama-c-discuss] Using a identifier in an "assumes" clause
  • From: belasri89 at gmail.com (mohamed belasri)
  • Date: Fri, 2 Mar 2012 17:30:13 +0100
Hi,

I tried to verify the following example by using an identifier (diff) to
simplify the assumption :
/*@
  @ behavior b1:
  @     assumes      \let diff=(a-b);         diff>=0;
  @     ensures \result==a;
  @ behavior b2:
  @     assumes      \let diff=(a-b);        diff<0;
  @     ensures \result==b;
  @ complete behaviors;
  @ disjoint behaviors;
  @*/

int max(int a, int b){
    if(a>=b)
        return a;
    else
        return b;
}

but I realized that the WP plug-in couldn't verify that the assumption
"diff>=0" is equivalent to "a>=b", so he could not verify for example that
\result==a.
However, we can easily verify the same function if don't use an identifier :
/*@
  @ behavior b1:
  @     assumes     (a-b)>=0;
  @     ensures \result==a;
  @ behavior b2:
  @     assumes    (a-b)<0;
  @     ensures \result==b;
  @ complete behaviors;
  @ disjoint behaviors;
  @*/

So, if anyone know why we have such a problem ...

Regards.
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