Method RandomSeed

Source/cmSystemTools.cxx:2919–2962

#endif

unsigned int cmSystemTools::RandomSeed()
{
#if defined(_WIN32) && !defined(__CYGWIN__)
  unsigned int seed = 0;

  // Try using a real random source.
  if (WinCryptRandom(&seed, sizeof(seed))) {
    return seed;
  }

  // Fall back to the time and pid.
  FILETIME ft;
  GetSystemTimeAsFileTime(&ft);
  unsigned int t1 = static_cast<unsigned int>(ft.dwHighDateTime);
  unsigned int t2 = static_cast<unsigned int>(ft.dwLowDateTime);
  unsigned int pid = static_cast<unsigned int>(GetCurrentProcessId());
  return t1 ^ t2 ^ pid;
#else
  union
  {
    unsigned int integer;
    char bytes[sizeof(unsigned int)];
  } seed;

  // Try using a real random source.
  cmsys::ifstream fin;
  fin.rdbuf()->pubsetbuf(nullptr, 0); // Unbuffered read.
  fin.open("/dev/urandom");
  if (fin.good() && fin.read(seed.bytes, sizeof(seed)) &&
      fin.gcount() == sizeof(seed)) {
    return seed.integer;
  }

  // Fall back to the time and pid.
  struct timeval t;
  gettimeofday(&t, nullptr);
  unsigned int pid = static_cast<unsigned int>(getpid());
  unsigned int tv_sec = static_cast<unsigned int>(t.tv_sec);
  unsigned int tv_usec = static_cast<unsigned int>(t.tv_usec);
  // Since tv_usec never fills more than 11 bits we shift it to fill
  // in the slow-changing high-order bits of tv_sec.
  return tv_sec ^ (tv_usec << 21) ^ pid;
#endif
}

unsigned int cmSystemTools::RandomNumber()
{