优化后的二次测试Miller_Rabin素性测试算法

ll random(ll n)
{
    return (ll)((double)rand()/RAND_MAX*n + 0.5);
}

ll pow_mod(ll a,ll p,ll n)
{
    if(p == 0)
        return 1;
    ll ans = pow_mod(a,p/2,n);
    ans = ans*ans%n;
    if(p%2)
        ans = ans*a%n;
    return ans;
}

bool Witness(ll a,ll n)
{
    ll m = n-1;
    int j = 0;
    while(!(m&1))
    {
        j++;
        m >>= 1;
    }
    ll x = pow_mod(a,m,n);
    if(x == 1 || x == n-1)
        return false;
    while(j--)
    {
        x = x*x%n;
        if(x == n-1)
            return false;
    }
    return true;
}

bool Miller_Rabin(ll n)
{
    if(n < 2)
        return false;
    if(n == 2)
        return true;
    if(!(n&1))
        return false;
    for(int i=1;i<=5;i++)   //5次测试
    {
        ll a = random(n-2)+1;
        if(Witness(a,n))
            return false;
    }
    return true;
}

int main()
{
    srand(time(NULL));
}