text: #ifndef SHA256_H
  #define SHA256_H
  #include <string>
  
  class SHA256
  {
  protected:
      typedef unsigned char uint8;
      typedef unsigned int uint32;
      typedef unsigned long long uint64;
  
      const static uint32 sha256_k[];
      static const unsigned int SHA224_256_BLOCK_SIZE = (512 / 8);
  public:
      void init();
      void update(const unsigned char* message, unsigned int len);
      void final(unsigned char* digest);
      static const unsigned int DIGEST_SIZE = (256 / 8);
  
  protected:
      void transform(const unsigned char* message, unsigned int block_nb);
      unsigned int m_tot_len;
      unsigned int m_len;
      unsigned char m_block[2 * SHA224_256_BLOCK_SIZE];
      uint32 m_h[8];
  };
  
  std::string sha256(std::string input);
  
  #define SHA2_SHFR(x, n)    (x >> n)
  #define SHA2_ROTR(x, n)   ((x >> n) | (x << ((sizeof(x) << 3) - n)))
  #define SHA2_ROTL(x, n)   ((x << n) | (x >> ((sizeof(x) << 3) - n)))
  #define SHA2_CH(x, y, z)  ((x & y) ^ (~x & z))
  #define SHA2_MAJ(x, y, z) ((x & y) ^ (x & z) ^ (y & z))
  #define SHA256_F1(x) (SHA2_ROTR(x,  2) ^ SHA2_ROTR(x, 13) ^ SHA2_ROTR(x, 22))
  #define SHA256_F2(x) (SHA2_ROTR(x,  6) ^ SHA2_ROTR(x, 11) ^ SHA2_ROTR(x, 25))
  #define SHA256_F3(x) (SHA2_ROTR(x,  7) ^ SHA2_ROTR(x, 18) ^ SHA2_SHFR(x,  3))
  #define SHA256_F4(x) (SHA2_ROTR(x, 17) ^ SHA2_ROTR(x, 19) ^ SHA2_SHFR(x, 10))
  #define SHA2_UNPACK32(x, str)                 \
  {                                             \
      *((str) + 3) = (uint8) ((x)      );       \
      *((str) + 2) = (uint8) ((x) >>  8);       \
      *((str) + 1) = (uint8) ((x) >> 16);       \
      *((str) + 0) = (uint8) ((x) >> 24);       \
  }
  #define SHA2_PACK32(str, x)                   \
  {                                             \
      *(x) =   ((uint32) *((str) + 3)      )    \
             | ((uint32) *((str) + 2) <<  8)    \
             | ((uint32) *((str) + 1) << 16)    \
             | ((uint32) *((str) + 0) << 24);   \
  }
  #endif