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

yukine (5)
Hi! So I was trying to create a test for numbers on primeness. But I keep getting a warning (Implicit conversion loses integer precision: 'long' to 'int') so that this doesn't run in console. Anything wrong here? Because I don't see any int in code.

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//---------------------------------------------------------------------------

#include <iostream>
#include <cmath>
#include <cstdlib>
#pragma hdrstop

using namespace std;
//---------------------------------------------------------------------------
long long mod( int number,  long long power,  long long n)
{
    unsigned long long res = 1;
    while (power)
    {
        if (power % 2)
            res = (res * number) % n;
        number = (number * number) % n;
        power /= 2;
    }
    return res;
}

long NOD(long m, long n)
{
    while(m!=0 && n!=0)
    {
        if(m>=n)
            m%=n;
        else
            n%=m;
    }
    return m+n;
}

long jacob_char(long a, long b)
{
    if (NOD(a, b) != 1)
        return 0;
    else
    {
        long r = 1;
        if (a < 0)
        {
            a = -a;
            if (b%4 == 3)
                r = -r;
        }
        do
        {
            long 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;
            long c = a;
            a = b%c;
            b = c;
        }
        while (a != 0);
        return r;
    }
}

int main(int argc, char* argv[])
{
    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)) /*Implicit conversion loses integer precision: 'long' to 'int'*/
        {
            
            flag=2;
            break;
        }
    }
    
    
    if (flag !=0)
    {
        cout<<"composite \n";
    }
    else
        cout<<"prime " << t << "\n";

    
    
    
    return 0;
}
Last edited on
jlb (4973)
Look at this snippet:

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...
long long mod( int number,  long long power,  long long n)
{
...

...
    long a;
...
        else if(mod(a, (n - 1) / 2, n) <= jacob_char(a, n)) /*Implicit conversion loses integer precision: 'long' to 'int'*/


You appear to be implicitly converting the variable a (a long) to an int in the function call.

You also have quite a few magic numbers (2 in the above snippet) that you should consider making named constants (using meaningful variable names) to document their purposes.

yukine (5)
Thanks. Dunno how i missed that
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