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// //////////////////////////////////////////////////////////
// md5.cpp
// Copyright (c) 2014,2015 Stephan Brumme. All rights reserved.
// see http://create.stephan-brumme.com/disclaimer.html
//

#include "hash/md5.h"

#ifndef _MSC_VER
#include <endian.h>
#endif


/// same as reset()
MD5::MD5()
{
  reset();
}


/// restart
void MD5::reset()
{
  m_numBytes   = 0;
  m_bufferSize = 0;

  // according to RFC 1321
  m_hash[0] = 0x67452301;
  m_hash[1] = 0xefcdab89;
  m_hash[2] = 0x98badcfe;
  m_hash[3] = 0x10325476;
}


namespace
{
  // mix functions for processBlock()
  inline uint32_t f1(uint32_t b, uint32_t c, uint32_t d)
  {
    return d ^ (b & (c ^ d)); // original: f = (b & c) | ((~b) & d);
  }

  inline uint32_t f2(uint32_t b, uint32_t c, uint32_t d)
  {
    return c ^ (d & (b ^ c)); // original: f = (b & d) | (c & (~d));
  }

  inline uint32_t f3(uint32_t b, uint32_t c, uint32_t d)
  {
    return b ^ c ^ d;
  }

  inline uint32_t f4(uint32_t b, uint32_t c, uint32_t d)
  {
    return c ^ (b | ~d);
  }

  inline uint32_t rotate(uint32_t a, uint32_t c)
  {
    return (a << c) | (a >> (32 - c));
  }

#if defined(__BYTE_ORDER) && (__BYTE_ORDER != 0) && (__BYTE_ORDER == __BIG_ENDIAN)
  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);
  }
#endif
}


/// process 64 bytes
void MD5::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];

  // data represented as 16x 32-bit words
  const uint32_t* words = (uint32_t*) data;

  // computations are little endian, swap data if necessary
#if defined(__BYTE_ORDER) && (__BYTE_ORDER != 0) && (__BYTE_ORDER == __BIG_ENDIAN)
#define LITTLEENDIAN(x) swap(x)
#else
#define LITTLEENDIAN(x) (x)
#endif

  // first round
  uint32_t word0  = LITTLEENDIAN(words[ 0]);
  a = rotate(a + f1(b,c,d) + word0  + 0xd76aa478,  7) + b;
  uint32_t word1  = LITTLEENDIAN(words[ 1]);
  d = rotate(d + f1(a,b,c) + word1  + 0xe8c7b756, 12) + a;
  uint32_t word2  = LITTLEENDIAN(words[ 2]);
  c = rotate(c + f1(d,a,b) + word2  + 0x242070db, 17) + d;
  uint32_t word3  = LITTLEENDIAN(words[ 3]);
  b = rotate(b + f1(c,d,a) + word3  + 0xc1bdceee, 22) + c;

  uint32_t word4  = LITTLEENDIAN(words[ 4]);
  a = rotate(a + f1(b,c,d) + word4  + 0xf57c0faf,  7) + b;
  uint32_t word5  = LITTLEENDIAN(words[ 5]);
  d = rotate(d + f1(a,b,c) + word5  + 0x4787c62a, 12) + a;
  uint32_t word6  = LITTLEENDIAN(words[ 6]);
  c = rotate(c + f1(d,a,b) + word6  + 0xa8304613, 17) + d;
  uint32_t word7  = LITTLEENDIAN(words[ 7]);
  b = rotate(b + f1(c,d,a) + word7  + 0xfd469501, 22) + c;

  uint32_t word8  = LITTLEENDIAN(words[ 8]);
  a = rotate(a + f1(b,c,d) + word8  + 0x698098d8,  7) + b;
  uint32_t word9  = LITTLEENDIAN(words[ 9]);
  d = rotate(d + f1(a,b,c) + word9  + 0x8b44f7af, 12) + a;
  uint32_t word10 = LITTLEENDIAN(words[10]);
  c = rotate(c + f1(d,a,b) + word10 + 0xffff5bb1, 17) + d;
  uint32_t word11 = LITTLEENDIAN(words[11]);
  b = rotate(b + f1(c,d,a) + word11 + 0x895cd7be, 22) + c;

  uint32_t word12 = LITTLEENDIAN(words[12]);
  a = rotate(a + f1(b,c,d) + word12 + 0x6b901122,  7) + b;
  uint32_t word13 = LITTLEENDIAN(words[13]);
  d = rotate(d + f1(a,b,c) + word13 + 0xfd987193, 12) + a;
  uint32_t word14 = LITTLEENDIAN(words[14]);
  c = rotate(c + f1(d,a,b) + word14 + 0xa679438e, 17) + d;
  uint32_t word15 = LITTLEENDIAN(words[15]);
  b = rotate(b + f1(c,d,a) + word15 + 0x49b40821, 22) + c;

  // second round
  a = rotate(a + f2(b,c,d) + word1  + 0xf61e2562,  5) + b;
  d = rotate(d + f2(a,b,c) + word6  + 0xc040b340,  9) + a;
  c = rotate(c + f2(d,a,b) + word11 + 0x265e5a51, 14) + d;
  b = rotate(b + f2(c,d,a) + word0  + 0xe9b6c7aa, 20) + c;

  a = rotate(a + f2(b,c,d) + word5  + 0xd62f105d,  5) + b;
  d = rotate(d + f2(a,b,c) + word10 + 0x02441453,  9) + a;
  c = rotate(c + f2(d,a,b) + word15 + 0xd8a1e681, 14) + d;
  b = rotate(b + f2(c,d,a) + word4  + 0xe7d3fbc8, 20) + c;

  a = rotate(a + f2(b,c,d) + word9  + 0x21e1cde6,  5) + b;
  d = rotate(d + f2(a,b,c) + word14 + 0xc33707d6,  9) + a;
  c = rotate(c + f2(d,a,b) + word3  + 0xf4d50d87, 14) + d;
  b = rotate(b + f2(c,d,a) + word8  + 0x455a14ed, 20) + c;

  a = rotate(a + f2(b,c,d) + word13 + 0xa9e3e905,  5) + b;
  d = rotate(d + f2(a,b,c) + word2  + 0xfcefa3f8,  9) + a;
  c = rotate(c + f2(d,a,b) + word7  + 0x676f02d9, 14) + d;
  b = rotate(b + f2(c,d,a) + word12 + 0x8d2a4c8a, 20) + c;

  // third round
  a = rotate(a + f3(b,c,d) + word5  + 0xfffa3942,  4) + b;
  d = rotate(d + f3(a,b,c) + word8  + 0x8771f681, 11) + a;
  c = rotate(c + f3(d,a,b) + word11 + 0x6d9d6122, 16) + d;
  b = rotate(b + f3(c,d,a) + word14 + 0xfde5380c, 23) + c;

  a = rotate(a + f3(b,c,d) + word1  + 0xa4beea44,  4) + b;
  d = rotate(d + f3(a,b,c) + word4  + 0x4bdecfa9, 11) + a;
  c = rotate(c + f3(d,a,b) + word7  + 0xf6bb4b60, 16) + d;
  b = rotate(b + f3(c,d,a) + word10 + 0xbebfbc70, 23) + c;

  a = rotate(a + f3(b,c,d) + word13 + 0x289b7ec6,  4) + b;
  d = rotate(d + f3(a,b,c) + word0  + 0xeaa127fa, 11) + a;
  c = rotate(c + f3(d,a,b) + word3  + 0xd4ef3085, 16) + d;
  b = rotate(b + f3(c,d,a) + word6  + 0x04881d05, 23) + c;

  a = rotate(a + f3(b,c,d) + word9  + 0xd9d4d039,  4) + b;
  d = rotate(d + f3(a,b,c) + word12 + 0xe6db99e5, 11) + a;
  c = rotate(c + f3(d,a,b) + word15 + 0x1fa27cf8, 16) + d;
  b = rotate(b + f3(c,d,a) + word2  + 0xc4ac5665, 23) + c;

  // fourth round
  a = rotate(a + f4(b,c,d) + word0  + 0xf4292244,  6) + b;
  d = rotate(d + f4(a,b,c) + word7  + 0x432aff97, 10) + a;
  c = rotate(c + f4(d,a,b) + word14 + 0xab9423a7, 15) + d;
  b = rotate(b + f4(c,d,a) + word5  + 0xfc93a039, 21) + c;

  a = rotate(a + f4(b,c,d) + word12 + 0x655b59c3,  6) + b;
  d = rotate(d + f4(a,b,c) + word3  + 0x8f0ccc92, 10) + a;
  c = rotate(c + f4(d,a,b) + word10 + 0xffeff47d, 15) + d;
  b = rotate(b + f4(c,d,a) + word1  + 0x85845dd1, 21) + c;

  a = rotate(a + f4(b,c,d) + word8  + 0x6fa87e4f,  6) + b;
  d = rotate(d + f4(a,b,c) + word15 + 0xfe2ce6e0, 10) + a;
  c = rotate(c + f4(d,a,b) + word6  + 0xa3014314, 15) + d;
  b = rotate(b + f4(c,d,a) + word13 + 0x4e0811a1, 21) + c;

  a = rotate(a + f4(b,c,d) + word4  + 0xf7537e82,  6) + b;
  d = rotate(d + f4(a,b,c) + word11 + 0xbd3af235, 10) + a;
  c = rotate(c + f4(d,a,b) + word2  + 0x2ad7d2bb, 15) + d;
  b = rotate(b + f4(c,d,a) + word9  + 0xeb86d391, 21) + c;

  // update hash
  m_hash[0] += a;
  m_hash[1] += b;
  m_hash[2] += c;
  m_hash[3] += d;
}


/// add arbitrary number of bytes
void MD5::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 MD5::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 little endian
  *addLength++ = msgBits & 0xFF; msgBits >>= 8;
  *addLength++ = msgBits & 0xFF; msgBits >>= 8;
  *addLength++ = msgBits & 0xFF; msgBits >>= 8;
  *addLength++ = msgBits & 0xFF; msgBits >>= 8;
  *addLength++ = msgBits & 0xFF; msgBits >>= 8;
  *addLength++ = msgBits & 0xFF; msgBits >>= 8;
  *addLength++ = msgBits & 0xFF; msgBits >>= 8;
  *addLength++ = msgBits & 0xFF;

  // process blocks
  processBlock(m_buffer);
  // flowed over into a second block ?
  if (paddedLength > BlockSize)
    processBlock(extra);
}


/// return latest hash as 32 hex characters
std::string MD5::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 MD5::getHash(unsigned char buffer[MD5::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]        & 0xFF;
    *current++ = (m_hash[i] >>  8) & 0xFF;
    *current++ = (m_hash[i] >> 16) & 0xFF;
    *current++ = (m_hash[i] >> 24) & 0xFF;

    // restore old hash
    m_hash[i] = oldHash[i];
  }
}


/// compute MD5 of a memory block
std::string MD5::operator()(const void* data, size_t numBytes)
{
  reset();
  add(data, numBytes);
  return getHash();
}


/// compute MD5 of a string, excluding final zero
std::string MD5::operator()(const std::string& text)
{
  reset();
  add(text.c_str(), text.size());
  return getHash();
}
