include/misc/dlist.h

/*
 * Copyright (c) 2013-2015 Wind River Systems, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/**
 * @file
 * @brief Doubly-linked list inline implementation
 *
 * Doubly-linked list implementation.
 *
 * The lists are expected to be initialized such that both the head and tail
 * pointers point to the list itself.  Initializing the lists in such a fashion
 * simplifies the adding and removing of nodes to/from the list.
 */

#ifndef _misc_dlist__h_
#define _misc_dlist__h_

#include <stddef.h>

#ifdef __cplusplus
extern "C" {
#endif

struct _dnode {
	union {
		struct _dnode *head; /* ptr to head of list (sys_dlist_t) */
		struct _dnode *next; /* ptr to next node    (sys_dnode_t) */
	};
	union {
		struct _dnode *tail; /* ptr to tail of list (sys_dlist_t) */
		struct _dnode *prev; /* ptr to previous node (sys_dnode_t) */
	};
};

typedef struct _dnode sys_dlist_t;
typedef struct _dnode sys_dnode_t;

/**
 * @brief initialize list
 *
 * @param list the doubly-linked list
 *
 * @return N/A
 */

static inline void sys_dlist_init(sys_dlist_t *list)
{
	list->head = (sys_dnode_t *)list;
	list->tail = (sys_dnode_t *)list;
}

/**
 * @brief check if a node is the list's head
 *
 * @param list the doubly-linked list to operate on
 * @param node the node to check
 *
 * @return 1 if node is the head, 0 otherwise
 */

static inline int sys_dlist_is_head(sys_dlist_t *list, sys_dnode_t *node)
{
	return list->head == node;
}

/**
 * @brief check if a node is the list's tail
 *
 * @param list the doubly-linked list to operate on
 * @param node the node to check
 *
 * @return 1 if node is the tail, 0 otherwise
 */

static inline int sys_dlist_is_tail(sys_dlist_t *list, sys_dnode_t *node)
{
	return list->tail == node;
}

/**
 * @brief check if the list is empty
 *
 * @param list the doubly-linked list to operate on
 *
 * @return 1 if empty, 0 otherwise
 */

static inline int sys_dlist_is_empty(sys_dlist_t *list)
{
	return list->head == list;
}

/**
 * @brief get a reference to the head item in the list
 *
 * @param list the doubly-linked list to operate on
 *
 * @return a pointer to the head element from a node, NULL if list is empty
 */

static inline sys_dnode_t *sys_dlist_peek_head(sys_dlist_t *list)
{
	return sys_dlist_is_empty(list) ? NULL : list->head;
}

/**
 * @brief get a reference to the next item in the list
 *
 * @param list the doubly-linked list to operate on
 * @param node the node from which to get the next element in the list
 *
 * @return a pointer to the next element from a node, NULL if node is the tail
 */

static inline sys_dnode_t *sys_dlist_peek_next(sys_dlist_t *list,
					       sys_dnode_t *node)
{
	return node == list->tail ? NULL : node->next;
}

/**
 * @brief add node to tail of list
 *
 * @param list the doubly-linked list to operate on
 * @param node the element to append
 *
 * @return N/A
 */

static inline void sys_dlist_append(sys_dlist_t *list, sys_dnode_t *node)
{
	node->next = list;
	node->prev = list->tail;

	list->tail->next = node;
	list->tail = node;
}

/**
 * @brief add node to head of list
 *
 * @param list the doubly-linked list to operate on
 * @param node the element to append
 *
 * @return N/A
 */

static inline void sys_dlist_prepend(sys_dlist_t *list, sys_dnode_t *node)
{
	node->next = list->head;
	node->prev = list;

	list->head->prev = node;
	list->head = node;
}

/**
 * @brief insert node after a node
 *
 * Insert a node after a specified node in a list.
 *
 * @param list the doubly-linked list to operate on
 * @param insert_point the insert point in the list: if NULL, insert at head
 * @param node the element to append
 *
 * @return N/A
 */

static inline void sys_dlist_insert_after(sys_dlist_t *list,
	sys_dnode_t *insert_point, sys_dnode_t *node)
{
	if (!insert_point) {
		sys_dlist_prepend(list, node);
	} else {
		node->next = insert_point->next;
		node->prev = insert_point;
		insert_point->next->prev = node;
		insert_point->next = node;
	}
}

/**
 * @brief insert node before a node
 *
 * Insert a node before a specified node in a list.
 *
 * @param list the doubly-linked list to operate on
 * @param insert_point the insert point in the list: if NULL, insert at tail
 * @param node the element to insert
 *
 * @return N/A
 */

static inline void sys_dlist_insert_before(sys_dlist_t *list,
	sys_dnode_t *insert_point, sys_dnode_t *node)
{
	if (!insert_point) {
		sys_dlist_append(list, node);
	} else {
		node->prev = insert_point->prev;
		node->next = insert_point;
		insert_point->prev->next = node;
		insert_point->prev = node;
	}
}

/**
 * @brief insert node at position
 *
 * Insert a node in a location depending on a external condition. The cond()
 * function checks if the node is to be inserted _before_ the current node
 * against which it is checked.
 *
 * @param list the doubly-linked list to operate on
 * @param node the element to insert
 * @param cond a function that determines if the current node is the correct
 *             insert point
 * @param data parameter to cond()
 *
 * @return N/A
 */

static inline void sys_dlist_insert_at(sys_dlist_t *list, sys_dnode_t *node,
	int (*cond)(sys_dnode_t *, void *), void *data)
{
	if (sys_dlist_is_empty(list)) {
		sys_dlist_append(list, node);
	} else {
		sys_dnode_t *pos = sys_dlist_peek_head(list);

		while (pos && !cond(pos, data)) {
			pos = sys_dlist_peek_next(list, pos);
		}
		sys_dlist_insert_before(list, pos, node);
	}
}

/**
 * @brief remove a specific node from a list
 *
 * The list is implicit from the node. The node must be part of a list.
 *
 * @param node the node to remove
 *
 * @return N/A
 */

static inline void sys_dlist_remove(sys_dnode_t *node)
{
	node->prev->next = node->next;
	node->next->prev = node->prev;
}

/**
 * @brief get the first node in a list
 *
 * @param list the doubly-linked list to operate on
 *
 * @return the first node in the list, NULL if list is empty
 */

static inline sys_dnode_t *sys_dlist_get(sys_dlist_t *list)
{
	sys_dnode_t *node;

	if (sys_dlist_is_empty(list)) {
		return NULL;
	}

	node = list->head;
	sys_dlist_remove(node);
	return node;
}

#ifdef __cplusplus
}
#endif

#endif /* _misc_dlist__h_ */