CRC32.h

/**
 * Implements CRC32 hashing for message verification
 */
template<unsigned int Size>
struct CRC32 {
public:
  /** Hash value */
  uint32_t crc = ~0L;

private:
  constexpr static uint32_t crc_table[16] = {
    0x00000000, 0x1db71064, 0x3b6e20c8, 0x26d930ac,
    0x76dc4190, 0x6b6b51f4, 0x4db26158, 0x5005713c,
    0xedb88320, 0xf00f9344, 0xd6d6a3e8, 0xcb61b38c,
    0x9b64c2b0, 0x86d3d2d4, 0xa00ae278, 0xbdbdf21c
  };

  void update(unsigned char data) {
    unsigned char tbl_idx;
    tbl_idx = crc ^ (data >> (0 * 4));
    crc = *(crc_table + (tbl_idx & 0x0f)) ^ (crc >> 4);
    tbl_idx = crc ^ (data >> (1 * 4));
    crc = *(crc_table + (tbl_idx & 0x0f)) ^ (crc >> 4);
  }

public:
  CRC32(char* s) {
    for (int i = 0; i < Size; i++)
      update(s[i]);
  }
};