CRC tables, generated at compile time using C++11 constexpr, C++14 utility library, variadic template, initializer list

gistfile1.cpp

// CRC tables, generated at compile time using C++11 constexpr, C++14 utility library, variadic template, initializer list
// Compiled and tested using msvc 2015, gcc 6.2, and clang 3.9.0.
// clang requires -std=c++14 -ftemplate-depth=512

#include <stdint.h>
#include <utility>

template<typename T, T Poly>
struct CrcTable {
  static constexpr T Generate(T v, int r = 8) {
    return r == 0 ? v : Generate((v >> 1) ^ (v & 1 ? Poly : 0), r - 1);
  }
  T m_V[256];
  template<T ...Is>
  constexpr CrcTable(std::integer_sequence<T, Is...>) : m_V{ Generate(Is)... } {}
  constexpr CrcTable() : CrcTable(std::make_integer_sequence<T, 256>()) {}
  constexpr T operator[](int i) const { return m_V[i]; }
};

constexpr CrcTable<uint32_t, 0xEDB88320> kCrcTable32;
constexpr CrcTable<uint64_t, 0xC96C5795D7870F42> kCrcTable64;