/*
*  lru lists are circular with a list head
*  pointing to the start and end of the list
*/
#include <u.h>
#include "lru.h"

/*
*  Create an lru chain of buffers
*/
void
lruinit(Lru *h)
{
       h->lprev = h->lnext = h;
}

/*
*  Add a member to an lru chain
*/
void
lruadd(Lru *h, Lru *m)
{
       h->lprev->lnext = m;
       m->lprev = h->lprev;
       h->lprev = m;
       m->lnext = h;
}

/*
*  Move to end of lru list
*/
void
lruref(Lru *h, Lru *m)
{
       if(h->lprev == m)
               return;         /* alread at end of list */

       /*
        *  remove from list
        */
       m->lprev->lnext = m->lnext;
       m->lnext->lprev = m->lprev;

       /*
        *  add in at end
        */
       h->lprev->lnext = m;
       m->lprev = h->lprev;
       h->lprev = m;
       m->lnext = h;
}

/*
*  Move to head of lru list
*/
void
lruderef(Lru *h, Lru *m)
{
       if(h->lnext == m)
               return;         /* alread at head of list */

       /*
        *  remove from list
        */
       m->lprev->lnext = m->lnext;
       m->lnext->lprev = m->lprev;

       /*
        *  add in at head
        */
       h->lnext->lprev = m;
       m->lnext = h->lnext;
       h->lnext = m;
       m->lprev = h;
}