// verifast_options{disable_overflow_check target:ILP32} extern void abort(void); //@ requires true; //@ ensures true; void reach_error() //@ requires false; //@ ensures true; {} /* * Implementation the Ackermann function. * http://en.wikipedia.org/wiki/Ackermann_function * * Author: Matthias Heizmann * Date: 2013-07-13 * * Copied from termination-numeric/Ackermann01_true-termination.c */ extern int __VERIFIER_nondet_int(void); //@ requires true; //@ ensures true; int ackermann(int m, int n) //@ requires true; //@ ensures (((0 < m) || ((m == 0) && ((n + 1) <= result))) && (((((((2 <= m) && (0 <= result)) && (n <= 0)) || ((m == 1) && (3 <= result))) || (m < 1)) || (((2 <= result) && (n <= 0)) && (m == 1))) || ((2 <= m) && (0 <= result)))); { if (m==0) { return n+1; } if (n==0) { return ackermann(m-1,1); } return ackermann(m-1,ackermann(m,n-1)); } int main() //@ requires module(Ackermann01_2__verifast_instrumented, true); //@ ensures junk(); { //@ open_module(); int m = __VERIFIER_nondet_int(); if (m < 0 || m > 3) { // additional branch to avoid undefined behavior // (because of signed integer overflow) return 0; } int n = __VERIFIER_nondet_int(); if (n < 0 || n > 23) { // additional branch to avoid undefined behavior // (because of signed integer overflow) // return 0; } int result = ackermann(m,n); if (m < 0 || n < 0 || result >= 0) { return 0; } else { ERROR: {reach_error();abort();} } return 0; }