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[Frama-c-discuss] Issue with modulo over unsigned int

  • Subject: [Frama-c-discuss] Issue with modulo over unsigned int
  • From: dmentre at linux-france.org (David MENTRE)
  • Date: Thu, 5 Mar 2009 12:01:04 +0100
Hello,

I have following code:
===
//@ ensures \result > 0 && \result < 4294967295;
unsigned int f(void)
{
  return 10;
}

void main(void)
{
  unsigned int a, b, r;

  a = f();
  b = f();
  //@ assert a > 0 && b > 0;
  r = a % b;
  //@ assert r < b;
}
===

With Alt-Ergo, I cannot prove "assert r < b" while this property seems
obvious to me as "r = a % b".

Is this a limitation of Alt-Ergo (Alt-Ergo does not know about modulo
mathematical properties) or am I missing something (e.g. Frama-C works
on mathematical integers which are different from unsigned int)?

Yours,
david