Function sweepgen

lib/lua/src/lgc.c:1115–1148

** Sweep for generational mode. Delete dead objects. (Because the ** collection is not incremental, there are no "new white" objects ** during the sweep. So, any white object must be dead.) For ** non-dead objects, advance their ages and clear the color of ** new objects. (Old objects keep their colors.) ** The ages of G_TOUCHED1 and G_TOUCHED2 objects cannot be advanced ** here, because these old

** will also remove objects turned white here from any gray list.
*/
static GCObject **sweepgen (lua_State *L, global_State *g, GCObject **p,
                            GCObject *limit, GCObject **pfirstold1) {
  static const lu_byte nextage[] = {
    G_SURVIVAL,  /* from G_NEW */
    G_OLD1,      /* from G_SURVIVAL */
    G_OLD1,      /* from G_OLD0 */
    G_OLD,       /* from G_OLD1 */
    G_OLD,       /* from G_OLD (do not change) */
    G_TOUCHED1,  /* from G_TOUCHED1 (do not change) */
    G_TOUCHED2   /* from G_TOUCHED2 (do not change) */
  };
  int white = luaC_white(g);
  GCObject *curr;
  while ((curr = *p) != limit) {
    if (iswhite(curr)) {  /* is 'curr' dead? */
      lua_assert(!isold(curr) && isdead(g, curr));
      *p = curr->next;  /* remove 'curr' from list */
      freeobj(L, curr);  /* erase 'curr' */
    }
    else {  /* correct mark and age */
      if (getage(curr) == G_NEW) {  /* new objects go back to white */
        int marked = curr->marked & ~maskgcbits;  /* erase GC bits */
        curr->marked = cast_byte(marked | G_SURVIVAL | white);
      }
      else {  /* all other objects will be old, and so keep their color */
        setage(curr, nextage[getage(curr)]);
        if (getage(curr) == G_OLD1 && *pfirstold1 == NULL)
          *pfirstold1 = curr;  /* first OLD1 object in the list */
      }
      p = &curr->next;  /* go to next element */
    }
  }
  return p;
}


/*