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标题: srand,random的疑问 [打印本页]

作者: hkdjining 时间: 2006-05-28 19:46
标题: srand,random的疑问
如果在linux下，用ticks = tv.tv_sec + tv.tv_usec;然后fd=open("/dev/urandom",O_RDONLY);接着进行了一个循环for (i=0;i<512;i++)
      {
      read(fd, &r, sizeof(r));
      ticks += r;
      }
然后用ticks做种子，我不明白打开那个文件并循环的目的是什么？只用ticks = tv.tv_sec + tv.tv_usec;难道不行吗？这个函数是不是能保证每次生成的随机数都不一样啊？还忘高手指教，谢谢了！
static unsigned int random_seed_set = 0;
unsigned int
osip_build_random_number ()
{
  if (!random_seed_set)
{
   unsigned int ticks;
#ifdef WIN32
   LARGE_INTEGER lCount;
   QueryPerformanceCounter(&lCount);
   ticks = lCount.LowPart + lCount.HighPart;
#elif defined(_WIN32_WCE)
   ticks = GetTickCount();
#else
   struct timeval tv;
   int fd;
   gettimeofday (&tv, NULL);
   ticks = tv.tv_sec + tv.tv_usec;
   fd=open("/dev/urandom",O_RDONLY);
   if (fd > 0)
{
      unsigned int r;
   int i;
      for (i=0;i<512;i++)
      {
      read(fd, &r, sizeof(r));
      ticks += r;
      }
   close(fd);
}
#endif

#ifdef HAVE_LRAND48
   srand48 (ticks);
#else
   srand (ticks);
#endif
   random_seed_set = 1;
}

#ifdef HAVE_LRAND48
  return lrand48 ();
#else
  return rand ();
#endif
}

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