[ECOS] how cyg_mtocl(x) and cyg_cltom(x) work?

[=?gb2312?B?1cUgwcE=?= <johnsonest at hotmail dot com>]

Hello, Mr. gthomas and everyone,
    I really do not know the principle of function mtocl(x)and cltom(x).
:
int
cyg_mtocl(u_long x)
{
   int res;
   res = (((u_long)(x) - (u_long)mbutl) >> MCLSHIFT);
   return res;
}

struct mbuf *
cyg_cltom(u_long x)
{
   struct mbuf *res;
   res = (struct mbuf *)((caddr_t)((u_long)mbutl + ((u_long)(x) << 
MCLSHIFT)));
   return res;
}

here,mbutl is a pointer to pointer to cluster memory pool,I really do not 
know
         (((u_long)(x) - (u_long)mbutl) >> MCLSHIFT and 
        ((caddr_t)((u_long)mbutl + ((u_long)(x) << MCLSHIFT
          mean what?
         because mbuf memory pool and cluster memory pool are two 
deffirent memory pool,so  add address or sub address means what?
SOS,please help me!
           
Brs/johnsonest


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