text: // //////////////////////////////////////////////////////////
  // sha256.cpp
  // Copyright (c) 2014,2015,2021 Stephan Brumme. All rights reserved.
  // see http://create.stephan-brumme.com/disclaimer.html
  //
  
  #include "sha256.h"
  
  // big endian architectures need #define __BYTE_ORDER __BIG_ENDIAN
  // #ifndef _MSC_VER
  // #include <endian.h>
  // #endif
  
  //#define SHA2_224_SEED_VECTOR
  
  
  /// same as reset()
  SHA256::SHA256()
  {
    reset();
  }
  
  
  /// restart
  void SHA256::reset()
  {
    m_numBytes   = 0;
    m_bufferSize = 0;
  
    // according to RFC 1321
    // "These words were obtained by taking the first thirty-two bits of the
    //  fractional parts of the square roots of the first eight prime numbers"
    m_hash[0] = 0x6a09e667;
    m_hash[1] = 0xbb67ae85;
    m_hash[2] = 0x3c6ef372;
    m_hash[3] = 0xa54ff53a;
    m_hash[4] = 0x510e527f;
    m_hash[5] = 0x9b05688c;
    m_hash[6] = 0x1f83d9ab;
    m_hash[7] = 0x5be0cd19;
  
  #ifdef SHA2_224_SEED_VECTOR
    // if you want SHA2-224 instead then use these seeds
    // and throw away the last 32 bits of getHash
    m_hash[0] = 0xc1059ed8;
    m_hash[1] = 0x367cd507;
    m_hash[2] = 0x3070dd17;
    m_hash[3] = 0xf70e5939;
    m_hash[4] = 0xffc00b31;
    m_hash[5] = 0x68581511;
    m_hash[6] = 0x64f98fa7;
    m_hash[7] = 0xbefa4fa4;
  #endif
  }
  
  
  namespace
  {
    inline uint32_t rotate(uint32_t a, uint32_t c)
    {
      return (a >> c) | (a << (32 - c));
    }
  
    inline uint32_t swap(uint32_t x)
    {
  #if defined(__GNUC__) || defined(__clang__)
      return __builtin_bswap32(x);
  #endif
  #ifdef MSC_VER
      return _byteswap_ulong(x);
  #endif
  
      return (x >> 24) |
            ((x >>  8) & 0x0000FF00) |
            ((x <<  8) & 0x00FF0000) |
             (x << 24);
    }
  
    // mix functions for processBlock()
    inline uint32_t f1(uint32_t e, uint32_t f, uint32_t g)
    {
      uint32_t term1 = rotate(e, 6) ^ rotate(e, 11) ^ rotate(e, 25);
      uint32_t term2 = (e & f) ^ (~e & g); //(g ^ (e & (f ^ g)))
      return term1 + term2;
    }
  
    inline uint32_t f2(uint32_t a, uint32_t b, uint32_t c)
    {
      uint32_t term1 = rotate(a, 2) ^ rotate(a, 13) ^ rotate(a, 22);
      uint32_t term2 = ((a | b) & c) | (a & b); //(a & (b ^ c)) ^ (b & c);
      return term1 + term2;
    }
  }
  
  
  /// process 64 bytes
  void SHA256::processBlock(const void* data)
  {
    // get last hash
    uint32_t a = m_hash[0];
    uint32_t b = m_hash[1];
    uint32_t c = m_hash[2];
    uint32_t d = m_hash[3];
    uint32_t e = m_hash[4];
    uint32_t f = m_hash[5];
    uint32_t g = m_hash[6];
    uint32_t h = m_hash[7];
  
    // data represented as 16x 32-bit words
    const uint32_t* input = (uint32_t*) data;
    // convert to big endian
    uint32_t words[64];
    int i;
    for (i = 0; i < 16; i++)
  #if defined(__BYTE_ORDER) && (__BYTE_ORDER != 0) && (__BYTE_ORDER == __BIG_ENDIAN)
      words[i] =      input[i];
  #else
      words[i] = swap(input[i]);
  #endif
  
    uint32_t x,y; // temporaries
  
    // first round
    x = h + f1(e,f,g) + 0x428a2f98 + words[ 0]; y = f2(a,b,c); d += x; h = x + y;
    x = g + f1(d,e,f) + 0x71374491 + words[ 1]; y = f2(h,a,b); c += x; g = x + y;
    x = f + f1(c,d,e) + 0xb5c0fbcf + words[ 2]; y = f2(g,h,a); b += x; f = x + y;
    x = e + f1(b,c,d) + 0xe9b5dba5 + words[ 3]; y = f2(f,g,h); a += x; e = x + y;
    x = d + f1(a,b,c) + 0x3956c25b + words[ 4]; y = f2(e,f,g); h += x; d = x + y;
    x = c + f1(h,a,b) + 0x59f111f1 + words[ 5]; y = f2(d,e,f); g += x; c = x + y;
    x = b + f1(g,h,a) + 0x923f82a4 + words[ 6]; y = f2(c,d,e); f += x; b = x + y;
    x = a + f1(f,g,h) + 0xab1c5ed5 + words[ 7]; y = f2(b,c,d); e += x; a = x + y;
  
    // secound round
    x = h + f1(e,f,g) + 0xd807aa98 + words[ 8]; y = f2(a,b,c); d += x; h = x + y;
    x = g + f1(d,e,f) + 0x12835b01 + words[ 9]; y = f2(h,a,b); c += x; g = x + y;
    x = f + f1(c,d,e) + 0x243185be + words[10]; y = f2(g,h,a); b += x; f = x + y;
    x = e + f1(b,c,d) + 0x550c7dc3 + words[11]; y = f2(f,g,h); a += x; e = x + y;
    x = d + f1(a,b,c) + 0x72be5d74 + words[12]; y = f2(e,f,g); h += x; d = x + y;
    x = c + f1(h,a,b) + 0x80deb1fe + words[13]; y = f2(d,e,f); g += x; c = x + y;
    x = b + f1(g,h,a) + 0x9bdc06a7 + words[14]; y = f2(c,d,e); f += x; b = x + y;
    x = a + f1(f,g,h) + 0xc19bf174 + words[15]; y = f2(b,c,d); e += x; a = x + y;
  
    // extend to 24 words
    for (; i < 24; i++)
      words[i] = words[i-16] +
                 (rotate(words[i-15],  7) ^ rotate(words[i-15], 18) ^ (words[i-15] >>  3)) +
                 words[i-7] +
                 (rotate(words[i- 2], 17) ^ rotate(words[i- 2], 19) ^ (words[i- 2] >> 10));
  
    // third round
    x = h + f1(e,f,g) + 0xe49b69c1 + words[16]; y = f2(a,b,c); d += x; h = x + y;
    x = g + f1(d,e,f) + 0xefbe4786 + words[17]; y = f2(h,a,b); c += x; g = x + y;
    x = f + f1(c,d,e) + 0x0fc19dc6 + words[18]; y = f2(g,h,a); b += x; f = x + y;
    x = e + f1(b,c,d) + 0x240ca1cc + words[19]; y = f2(f,g,h); a += x; e = x + y;
    x = d + f1(a,b,c) + 0x2de92c6f + words[20]; y = f2(e,f,g); h += x; d = x + y;
    x = c + f1(h,a,b) + 0x4a7484aa + words[21]; y = f2(d,e,f); g += x; c = x + y;
    x = b + f1(g,h,a) + 0x5cb0a9dc + words[22]; y = f2(c,d,e); f += x; b = x + y;
    x = a + f1(f,g,h) + 0x76f988da + words[23]; y = f2(b,c,d); e += x; a = x + y;
  
    // extend to 32 words
    for (; i < 32; i++)
      words[i] = words[i-16] +
                 (rotate(words[i-15],  7) ^ rotate(words[i-15], 18) ^ (words[i-15] >>  3)) +
                 words[i-7] +
                 (rotate(words[i- 2], 17) ^ rotate(words[i- 2], 19) ^ (words[i- 2] >> 10));
  
    // fourth round
    x = h + f1(e,f,g) + 0x983e5152 + words[24]; y = f2(a,b,c); d += x; h = x + y;
    x = g + f1(d,e,f) + 0xa831c66d + words[25]; y = f2(h,a,b); c += x; g = x + y;
    x = f + f1(c,d,e) + 0xb00327c8 + words[26]; y = f2(g,h,a); b += x; f = x + y;
    x = e + f1(b,c,d) + 0xbf597fc7 + words[27]; y = f2(f,g,h); a += x; e = x + y;
    x = d + f1(a,b,c) + 0xc6e00bf3 + words[28]; y = f2(e,f,g); h += x; d = x + y;
    x = c + f1(h,a,b) + 0xd5a79147 + words[29]; y = f2(d,e,f); g += x; c = x + y;
    x = b + f1(g,h,a) + 0x06ca6351 + words[30]; y = f2(c,d,e); f += x; b = x + y;
    x = a + f1(f,g,h) + 0x14292967 + words[31]; y = f2(b,c,d); e += x; a = x + y;
  
    // extend to 40 words
    for (; i < 40; i++)
      words[i] = words[i-16] +
                 (rotate(words[i-15],  7) ^ rotate(words[i-15], 18) ^ (words[i-15] >>  3)) +
                 words[i-7] +
                 (rotate(words[i- 2], 17) ^ rotate(words[i- 2], 19) ^ (words[i- 2] >> 10));
  
    // fifth round
    x = h + f1(e,f,g) + 0x27b70a85 + words[32]; y = f2(a,b,c); d += x; h = x + y;
    x = g + f1(d,e,f) + 0x2e1b2138 + words[33]; y = f2(h,a,b); c += x; g = x + y;
    x = f + f1(c,d,e) + 0x4d2c6dfc + words[34]; y = f2(g,h,a); b += x; f = x + y;
    x = e + f1(b,c,d) + 0x53380d13 + words[35]; y = f2(f,g,h); a += x; e = x + y;
    x = d + f1(a,b,c) + 0x650a7354 + words[36]; y = f2(e,f,g); h += x; d = x + y;
    x = c + f1(h,a,b) + 0x766a0abb + words[37]; y = f2(d,e,f); g += x; c = x + y;
    x = b + f1(g,h,a) + 0x81c2c92e + words[38]; y = f2(c,d,e); f += x; b = x + y;
    x = a + f1(f,g,h) + 0x92722c85 + words[39]; y = f2(b,c,d); e += x; a = x + y;
  
    // extend to 48 words
    for (; i < 48; i++)
      words[i] = words[i-16] +
                 (rotate(words[i-15],  7) ^ rotate(words[i-15], 18) ^ (words[i-15] >>  3)) +
                 words[i-7] +
                 (rotate(words[i- 2], 17) ^ rotate(words[i- 2], 19) ^ (words[i- 2] >> 10));
  
    // sixth round
    x = h + f1(e,f,g) + 0xa2bfe8a1 + words[40]; y = f2(a,b,c); d += x; h = x + y;
    x = g + f1(d,e,f) + 0xa81a664b + words[41]; y = f2(h,a,b); c += x; g = x + y;
    x = f + f1(c,d,e) + 0xc24b8b70 + words[42]; y = f2(g,h,a); b += x; f = x + y;
    x = e + f1(b,c,d) + 0xc76c51a3 + words[43]; y = f2(f,g,h); a += x; e = x + y;
    x = d + f1(a,b,c) + 0xd192e819 + words[44]; y = f2(e,f,g); h += x; d = x + y;
    x = c + f1(h,a,b) + 0xd6990624 + words[45]; y = f2(d,e,f); g += x; c = x + y;
    x = b + f1(g,h,a) + 0xf40e3585 + words[46]; y = f2(c,d,e); f += x; b = x + y;
    x = a + f1(f,g,h) + 0x106aa070 + words[47]; y = f2(b,c,d); e += x; a = x + y;
  
    // extend to 56 words
    for (; i < 56; i++)
      words[i] = words[i-16] +
                 (rotate(words[i-15],  7) ^ rotate(words[i-15], 18) ^ (words[i-15] >>  3)) +
                 words[i-7] +
                 (rotate(words[i- 2], 17) ^ rotate(words[i- 2], 19) ^ (words[i- 2] >> 10));
  
    // seventh round
    x = h + f1(e,f,g) + 0x19a4c116 + words[48]; y = f2(a,b,c); d += x; h = x + y;
    x = g + f1(d,e,f) + 0x1e376c08 + words[49]; y = f2(h,a,b); c += x; g = x + y;
    x = f + f1(c,d,e) + 0x2748774c + words[50]; y = f2(g,h,a); b += x; f = x + y;
    x = e + f1(b,c,d) + 0x34b0bcb5 + words[51]; y = f2(f,g,h); a += x; e = x + y;
    x = d + f1(a,b,c) + 0x391c0cb3 + words[52]; y = f2(e,f,g); h += x; d = x + y;
    x = c + f1(h,a,b) + 0x4ed8aa4a + words[53]; y = f2(d,e,f); g += x; c = x + y;
    x = b + f1(g,h,a) + 0x5b9cca4f + words[54]; y = f2(c,d,e); f += x; b = x + y;
    x = a + f1(f,g,h) + 0x682e6ff3 + words[55]; y = f2(b,c,d); e += x; a = x + y;
  
    // extend to 64 words
    for (; i < 64; i++)
      words[i] = words[i-16] +
                 (rotate(words[i-15],  7) ^ rotate(words[i-15], 18) ^ (words[i-15] >>  3)) +
                 words[i-7] +
                 (rotate(words[i- 2], 17) ^ rotate(words[i- 2], 19) ^ (words[i- 2] >> 10));
  
    // eigth round
    x = h + f1(e,f,g) + 0x748f82ee + words[56]; y = f2(a,b,c); d += x; h = x + y;
    x = g + f1(d,e,f) + 0x78a5636f + words[57]; y = f2(h,a,b); c += x; g = x + y;
    x = f + f1(c,d,e) + 0x84c87814 + words[58]; y = f2(g,h,a); b += x; f = x + y;
    x = e + f1(b,c,d) + 0x8cc70208 + words[59]; y = f2(f,g,h); a += x; e = x + y;
    x = d + f1(a,b,c) + 0x90befffa + words[60]; y = f2(e,f,g); h += x; d = x + y;
    x = c + f1(h,a,b) + 0xa4506ceb + words[61]; y = f2(d,e,f); g += x; c = x + y;
    x = b + f1(g,h,a) + 0xbef9a3f7 + words[62]; y = f2(c,d,e); f += x; b = x + y;
    x = a + f1(f,g,h) + 0xc67178f2 + words[63]; y = f2(b,c,d); e += x; a = x + y;
  
    // update hash
    m_hash[0] += a;
    m_hash[1] += b;
    m_hash[2] += c;
    m_hash[3] += d;
    m_hash[4] += e;
    m_hash[5] += f;
    m_hash[6] += g;
    m_hash[7] += h;
  }
  
  
  /// add arbitrary number of bytes
  void SHA256::add(const void* data, size_t numBytes)
  {
    const uint8_t* current = (const uint8_t*) data;
  
    if (m_bufferSize > 0)
    {
      while (numBytes > 0 && m_bufferSize < BlockSize)
      {
        m_buffer[m_bufferSize++] = *current++;
        numBytes--;
      }
    }
  
    // full buffer
    if (m_bufferSize == BlockSize)
    {
      processBlock(m_buffer);
      m_numBytes  += BlockSize;
      m_bufferSize = 0;
    }
  
    // no more data ?
    if (numBytes == 0)
      return;
  
    // process full blocks
    while (numBytes >= BlockSize)
    {
      processBlock(current);
      current    += BlockSize;
      m_numBytes += BlockSize;
      numBytes   -= BlockSize;
    }
  
    // keep remaining bytes in buffer
    while (numBytes > 0)
    {
      m_buffer[m_bufferSize++] = *current++;
      numBytes--;
    }
  }
  
  
  /// process final block, less than 64 bytes
  void SHA256::processBuffer()
  {
    // the input bytes are considered as bits strings, where the first bit is the most significant bit of the byte
  
    // - append "1" bit to message
    // - append "0" bits until message length in bit mod 512 is 448
    // - append length as 64 bit integer
  
    // number of bits
    size_t paddedLength = m_bufferSize * 8;
  
    // plus one bit set to 1 (always appended)
    paddedLength++;
  
    // number of bits must be (numBits % 512) = 448
    size_t lower11Bits = paddedLength & 511;
    if (lower11Bits <= 448)
      paddedLength +=       448 - lower11Bits;
    else
      paddedLength += 512 + 448 - lower11Bits;
    // convert from bits to bytes
    paddedLength /= 8;
  
    // only needed if additional data flows over into a second block
    unsigned char extra[BlockSize];
  
    // append a "1" bit, 128 => binary 10000000
    if (m_bufferSize < BlockSize)
      m_buffer[m_bufferSize] = 128;
    else
      extra[0] = 128;
  
    size_t i;
    for (i = m_bufferSize + 1; i < BlockSize; i++)
      m_buffer[i] = 0;
    for (; i < paddedLength; i++)
      extra[i - BlockSize] = 0;
  
    // add message length in bits as 64 bit number
    uint64_t msgBits = 8 * (m_numBytes + m_bufferSize);
    // find right position
    unsigned char* addLength;
    if (paddedLength < BlockSize)
      addLength = m_buffer + paddedLength;
    else
      addLength = extra + paddedLength - BlockSize;
  
    // must be big endian
    *addLength++ = (unsigned char)((msgBits >> 56) & 0xFF);
    *addLength++ = (unsigned char)((msgBits >> 48) & 0xFF);
    *addLength++ = (unsigned char)((msgBits >> 40) & 0xFF);
    *addLength++ = (unsigned char)((msgBits >> 32) & 0xFF);
    *addLength++ = (unsigned char)((msgBits >> 24) & 0xFF);
    *addLength++ = (unsigned char)((msgBits >> 16) & 0xFF);
    *addLength++ = (unsigned char)((msgBits >>  8) & 0xFF);
    *addLength   = (unsigned char)( msgBits        & 0xFF);
  
    // process blocks
    processBlock(m_buffer);
    // flowed over into a second block ?
    if (paddedLength > BlockSize)
      processBlock(extra);
  }
  
  
  /// return latest hash as 64 hex characters
  std::string SHA256::getHash()
  {
    // compute hash (as raw bytes)
    unsigned char rawHash[HashBytes];
    getHash(rawHash);
  
    // convert to hex string
    std::string result;
    result.reserve(2 * HashBytes);
    for (int i = 0; i < HashBytes; i++)
    {
      static const char dec2hex[16+1] = "0123456789abcdef";
      result += dec2hex[(rawHash[i] >> 4) & 15];
      result += dec2hex[ rawHash[i]       & 15];
    }
  
    return result;
  }
  
  
  /// return latest hash as bytes
  void SHA256::getHash(unsigned char buffer[SHA256::HashBytes])
  {
    // save old hash if buffer is partially filled
    uint32_t oldHash[HashValues];
    for (int i = 0; i < HashValues; i++)
      oldHash[i] = m_hash[i];
  
    // process remaining bytes
    processBuffer();
  
    unsigned char* current = buffer;
    for (int i = 0; i < HashValues; i++)
    {
      *current++ = (m_hash[i] >> 24) & 0xFF;
      *current++ = (m_hash[i] >> 16) & 0xFF;
      *current++ = (m_hash[i] >>  8) & 0xFF;
      *current++ =  m_hash[i]        & 0xFF;
  
      // restore old hash
      m_hash[i] = oldHash[i];
    }
  }
  
  
  /// compute SHA256 of a memory block
  std::string SHA256::operator()(const void* data, size_t numBytes)
  {
    reset();
    add(data, numBytes);
    return getHash();
  }
  
  
  /// compute SHA256 of a string, excluding final zero
  std::string SHA256::operator()(const std::string& text)
  {
    reset();
    add(text.c_str(), text.size());
    return getHash();
  }
  