C++ header to calculate pow(B,E) at compiletime in O(log(E))

metapow.hpp

#pragma once


#if __cplusplus > 199711L

#include <cstdint>

constexpr uint64_t pow_impl(uint64_t B, uint64_t E, uint64_t res = 1)
{
  return E < 1 ? res : pow_impl(B*B, E/2, E%2 ? B*res : res);
}

template<uint64_t B, uint64_t E>
struct Pow
{
    static constexpr uint64_t value = pow_impl(B, E);
};

#else

#define SQ(a)   ((a)*(a))
#include <stdint.h>

template<uint64_t B, uint64_t E>
struct Pow;

template<uint64_t B>
struct Pow<B, 0>
{
    static const uint64_t value = 1;
};

template<uint64_t B, uint64_t E>
struct Pow
{
private:
    static const uint64_t v0 = Pow<B, E/2>::value;

public:
    static const uint64_t value = SQ(v0)*(E%2 ? B : 1);
};

#endif