extern int __VERIFIER_nondet_int(); void abort() { }; /*@ requires (1); ensures ((((((((((\result == 3) && (4 == n)) || ((2 == n) && (\result == 1))) || (n < 1)) || ((3 == n) && (\result == 2))) || (5 < n)) || ((\result == 1) && (1 == n))) || ((\result == 5) && (5 == n))) && ((0 < n) || (\result == 0)))); @*/ int fibo(int n) { if (n < 1) { return 0; } else if (n == 1) { return 1; } else { return fibo(n-1) + fibo(n-2); } } // fibo 1-30 // 1, 1, 2, 3, 5, // 8, 13, 21, 34, 55, // 89, 144, 233, 377, 610, // 987, 1597, 2584, 4181, 6765, // 10946, 17711, 28657, 46368, 75025, // 121393, 196418, 317811, 514229, 832040 int main() { int x = 5; int result = fibo(x); if (result != 5) { ERROR: {/*@ assert(0); */;abort();} } return 0; }