Implicit conversion loses integer precision: 'long' to 'int'

[yukine]

hi! I was trying to make a prime number test and this warning came out.
I surfed the web and found no possible fixes for this.
Implicit conversion loses integer precision: 'long' to 'int'
on line: else if (mod(a,(n-1)/2,n) <= jacob_char(a, n))
Any possible fixes, pls?

  int main(int argc, char* argv[])
{
    long PerformCalculation(void);
    long n;
    long k;
    long a;
    double t;
    int flag = 0;
    
    cin>>n;
    cin>>k;
    t=1-1/pow(2.0,k);
    
    for (int i=1; i <= k; i++)
    {
        a=rand()%(n-2)+2;
        if (NOD(a, n) > 1)
        {
            
            flag=1;
            break;
        }
        else if (mod(a,(n-1)/2,n) <= jacob_char(a, n))
        {
            
            flag=2;
            break;
        }
    }
    
    
    if (flag !=0)
    {
        cout<<"not prime \n";
    }
    else
        cout<<"prime with probability of = " << t << "\n";

    
    
    
    return 0;
}

[jonnin]

make the int a long.
it is telling you that (for example) if you have a 64 bit integer and assign that value to a 32 bit integer, it may not work because it may not fit. If the actual value fits into a 32 bit int, its just a warning you can ignore. If not, it will give incorrect results. Better to just make them all the same size, get rid of both the warning and the potential bug.

[yukine]

thanks, thought the main problem is that i don't realise where are the ints are, like as u can see, there are only longs in the main and in the modulus or its a jacob_char?

int jacob_char(int a, int b)
{
    if (NOD(a, b) != 1)
        return 0;
    else
    {
        int r = 1;
        if (a < 0)
        {
            a = -a;
            if (b%4 == 3)
                r = -r;
        }
        do
        {
            int t = 0;
            while (a%2 == 0)
            {
                t += 1;
                a /= 2;
            }
            if (t%2 != 0 && (b%8 == 3 || b%8 == 5))
                r = -r;
            if (a%4 == 3 && b%4 == 3)
                r = -r;
            int c = a;
            a = b%c;
            b = c;
        }
        while (a != 0);
        return r;
    }
}

[jonnin]

I will help you to see it:

long n;
long a;
..CHOP
else if (mod(a,(n-1)/2,n) <= jacob_char(a, n))

vs:
int jacob_char(int a, int b)

the act of calling jacob_char with a long and stuffing it into an int is at least one place for this warning/complaint.