求大神帮忙看一下这段程序的意思吧！跪着！马上要答辩了啊！！！

void long_to_str(unsigned long dat)
{
unsigned char tmp,i;
unsigned long dd;
unsigned char *ss = buf;
dd = dat;
for(i = 0;i<8;i++)
{
tmp = (unsigned char)(dd>>28&0xf);
if(tmp <10)
{
*ss = tmp+0x30
}
else
{
*ss = 65+(tmp-10);
}
ss++;
dd = dd <<4;//(dd左移四次）
}
*ss = 0;
}