extern void __VERIFIER_error() __attribute__ ((__noreturn__)); /* * Recursive implementation of the greatest common denominator * using Euclid's algorithm * * Author: Jan Leike * Date: 2013-07-17 * */ extern int __VERIFIER_nondet_int(void); // Compute the greatest common denominator using Euclid's algorithm int gcd(int y1, int y2) { if (y1 <= 0 || y2 <= 0) { // No non-positive input allowed ERROR: __VERIFIER_error(); } if (y1 == y2) { return y1; } if (y1 > y2) { return gcd(y1 - y2, y2); } return gcd(y1, y2 - y1); } // does n divide m? int divides(int n, int m) { if (m == 0) { return 1; // true } if (n > m) { return 0; // false } return divides(n, m - n); } int main() { int m = __VERIFIER_nondet_int(); if (m <= 0 || m > 2147483647) { return 0; } int n = __VERIFIER_nondet_int(); if (n <= 0 || n > 2147483647) { return 0; } if (m > 0 && n > 0) { int z = gcd(m, n); if (divides(z, m) == 0) { ERROR: __VERIFIER_error(); } else { return 0; } } }