xtea

xtea.h

#pragma once
#include <cstdint>

struct xtea_t
{
  static const uint32_t _delta = 0x9E3779B9;

  typedef uint32_t key_t[4];

  template <uint32_t num_rounds>
  void encipher(uint32_t v[2], const key_t &key)
  {
    uint32_t v0 = v[0], v1 = v[1], sum = 0;
    for (uint32_t i = 0; i < num_rounds; i++) {
      v0 += (((v1 << 4) ^ (v1 >> 5)) + v1) ^ (sum + key[3 & sum]);
      sum += _delta;
      v1 += (((v0 << 4) ^ (v0 >> 5)) + v0) ^ (sum + key[3 & (sum >> 11)]);
    }
    v[0] = v0, v[1] = v1;
  }

  template <uint32_t num_rounds>
  void decipher(uint32_t v[2], const key_t &key)
  {
    uint32_t v0 = v[0], v1 = v[1], sum = delta * num_rounds;
    for (uint32_t i = 0; i < num_rounds; i++) {
      v1 -= (((v0 << 4) ^ (v0 >> 5)) + v0) ^ (sum + key[3 & (sum >> 11)]);
      sum -= _delta;
      v0 -= (((v1 << 4) ^ (v1 >> 5)) + v1) ^ (sum + key[3 & sum]);
    }
    v[0] = v0, v[1] = v1;
  }
};