双向链表算法。
本双向链表的所有元素存储在一个pool中,根据pool中内存块的序号进行索引。
typedef struct
{
u32 next;
u32 prev;
u32 value;
} dlist_elt_t;
本双向链表中每一个元素的结构。value指的是元素的值。
next, prev分别代表前一个和后一个元素。它们的语义是元素在内存池中的编号,通俗的说,就是数组的下标。
static inline void
clib_dlist_init (dlist_elt_t * pool, u32 index)
{
dlist_elt_t *head = pool_elt_at_index (pool, index);
memset (head, 0xFF, sizeof (*head));
}
初始状态,将头部节点的value置为全1bit。头部节点为一个哑节点,无实际数据,只是用来辅助形成链表。
static inline void
clib_dlist_addtail (dlist_elt_t * pool, u32 head_index, u32 new_index)
{
dlist_elt_t *head = pool_elt_at_index (pool, head_index);
u32 old_last_index;
dlist_elt_t *old_last;
dlist_elt_t *new;
ASSERT (head->value == ~0);
new = pool_elt_at_index (pool, new_index);
if (PREDICT_FALSE (head->next == ~0))
{
head->next = head->prev = new_index;
new->next = new->prev = head_index;
return;
}
old_last_index = head->prev;
old_last = pool_elt_at_index (pool, old_last_index);
new->next = old_last->next;
new->prev = old_last_index;
old_last->next = new_index;
head->prev = new_index;
}
新节点插入空链表的情况下,哑头节点与新节点互相指向,形成环状。
新节点插入非空链表的情况下,新节点插入尾部节点与哑头之间,新节点成为新的尾部节点
static inline void
clib_dlist_addhead (dlist_elt_t * pool, u32 head_index, u32 new_index)
{
dlist_elt_t *head = pool_elt_at_index (pool, head_index);
dlist_elt_t *old_first;
u32 old_first_index;
dlist_elt_t *new;
ASSERT (head->value == ~0);
new = pool_elt_at_index (pool, new_index);
if (PREDICT_FALSE (head->next == ~0))
{
head->next = head->prev = new_index;
new->next = new->prev = head_index;
return;
}
old_first_index = head->next;
old_first = pool_elt_at_index (pool, old_first_index);
new->next = old_first_index;
new->prev = old_first->prev;
old_first->prev = new_index;
head->next = new_index;
}
在双链表头部插入新节点,空链表插入的情形与上一个函数类似。
非空链表上插入时,新节点插入哑头节点与第1个数据节点之间。新节点成为第1个数据节点,原节点成为第2个数据节点。
static inline void
clib_dlist_remove (dlist_elt_t * pool, u32 index)
{
dlist_elt_t *elt = pool_elt_at_index (pool, index);
dlist_elt_t *next_elt, *prev_elt;
/* listhead, not so much */
ASSERT (elt->value != ~0);
next_elt = pool_elt_at_index (pool, elt->next);
prev_elt = pool_elt_at_index (pool, elt->prev);
next_elt->prev = elt->prev;
prev_elt->next = elt->next;
elt->prev = elt->next = ~0;
}
删除双向链表中的一个数据节点。其实就是讲此数据节点之前和之后的节点连接起来(有可能是哑头节点)
static inline u32
clib_dlist_remove_head (dlist_elt_t * pool, u32 head_index)
{
dlist_elt_t *head = pool_elt_at_index (pool, head_index);
u32 rv;
ASSERT (head->value == ~0);
if (head->next == ~0 || (head->next == head_index))
return ~0;
rv = head->next;
clib_dlist_remove (pool, rv);
return rv;
}
删除链表头部的第1个数据节点,如果只有哑头,则空操作
static inline u32
clib_dlist_remove_tail (dlist_elt_t * pool, u32 head_index)
{
dlist_elt_t *head = pool_elt_at_index (pool, head_index);
u32 rv;
ASSERT (head->value == ~0);
if (head->prev == ~0)
return ~0;
rv = head->prev;
clib_dlist_remove (pool, rv);
return rv;
}
删除链表尾部的数据节点,如果只有一个哑头,则空操作。