fast exponentiation, cp time

/* 
* A fast exponentiation. 
* The algo has O(log(m)) time complexity, additionally it gets a boost because of compile time.
*/

template <int n, int mod, int debug_info, int m>
 struct fast_exp {
     static constexpr int value = (m % 2 == 0) ? fast_exp<(n * n) % mod, mod, debug_info, m / 2>::value : (n * fast_exp<(n * n) % mod, mod, debug_info,   (m - 1) / 2>::value) % mod;
     static constexpr void run_debug() {
         static_assert(value == debug_info, "failed");
     }   
 };
 
 template <int n, int mod, int debug_info>
 struct fast_exp<n, mod, debug_info, 0> {
     static constexpr int value = 1;
 };