// verifast_options{disable_overflow_check target:ILP32}
/* shift_add algorithm for computing the 
   product of two natural numbers
*/
extern void abort(void);
//@ requires true;
//@ ensures true;
void reach_error()
//@ requires false;
//@ ensures true;
{}extern int __VERIFIER_nondet_int(void);
//@ requires true;
//@ ensures true;
void assume_abort_if_not(int cond) 
//@ requires true;
//@ ensures (cond != 0);
{  if(!cond) {abort();}
}
void __VERIFIER_assert(int cond) 
//@ requires (1 <= cond);
//@ ensures (1 <= cond);
{    if (!(cond)) {
    ERROR:
        {reach_error();}
    }
    return;
}

int main() 
//@ requires module(prodbin_ll_valuebound100__verifast_instrumented, true);
//@ ensures junk();
{
    //@ open_module(); 
    int a, b;
    long long x, y, z;

    a = __VERIFIER_nondet_int();
    assume_abort_if_not(a>=0 && a<=100);
    b = __VERIFIER_nondet_int();
    assume_abort_if_not(b>=0 && b<=100);
    assume_abort_if_not(b >= 1);

    x = a;
    y = b;
    z = 0;

while (1)
//@ invariant (((((0 <= y) && ((z + (y * x)) == (b * a))) && (a <= 100)) && (0 <= a)) && (1 <= b));
    {
        __VERIFIER_assert(z + x * y == (long long) a * b);
        if (!(y != 0))
            break;

        if (y % 2 == 1) {
            z = z + x;
            y = y - 1;
        }
        x = 2 * x;
        y = y / 2;
    }
    __VERIFIER_assert(z == (long long) a * b);
    
    return 0;
}