F(n)^xmod n code example

Example: how to calculate pisano period

long long get_pisano_period(long long m) {
    long long a = 0, b = 1, c = a + b;
    for (int i = 0; i < m * m; i++) {
        c = (a + b) % m;
        a = b;
        b = c;
        if (a == 0 && b == 1) return i + 1;
    }
}