/*
   * Copyright (c) 1991, 1993
   *	The Regents of the University of California.  All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   *
   * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   *
   *	@(#)queue.h	8.5 (Berkeley) 8/20/94
   * $FreeBSD: src/sys/sys/queue.h,v 1.38 2000/05/26 02:06:56 jake Exp $
   */
  
  #ifndef _SYS_QUEUE_H_
  #define	_SYS_QUEUE_H_
  
  /*
   * This file defines five types of data structures: singly-linked lists,
   * singly-linked tail queues, lists, tail queues, and circular queues.
   *
   * A singly-linked list is headed by a single forward pointer. The elements
   * are singly linked for minimum space and pointer manipulation overhead at
   * the expense of O(n) removal for arbitrary elements. New elements can be
   * added to the list after an existing element or at the head of the list.
   * Elements being removed from the head of the list should use the explicit
   * macro for this purpose for optimum efficiency. A singly-linked list may
   * only be traversed in the forward direction.  Singly-linked lists are ideal
   * for applications with large datasets and few or no removals or for
   * implementing a LIFO queue.
   *
   * A singly-linked tail queue is headed by a pair of pointers, one to the
   * head of the list and the other to the tail of the list. The elements are
   * singly linked for minimum space and pointer manipulation overhead at the
   * expense of O(n) removal for arbitrary elements. New elements can be added
   * to the list after an existing element, at the head of the list, or at the
   * end of the list. Elements being removed from the head of the tail queue
   * should use the explicit macro for this purpose for optimum efficiency.
   * A singly-linked tail queue may only be traversed in the forward direction.
   * Singly-linked tail queues are ideal for applications with large datasets
   * and few or no removals or for implementing a FIFO queue.
   *
   * A list is headed by a single forward pointer (or an array of forward
   * pointers for a hash table header). The elements are doubly linked
   * so that an arbitrary element can be removed without a need to
   * traverse the list. New elements can be added to the list before
   * or after an existing element or at the head of the list. A list
   * may only be traversed in the forward direction.
   *
   * A tail queue is headed by a pair of pointers, one to the head of the
   * list and the other to the tail of the list. The elements are doubly
   * linked so that an arbitrary element can be removed without a need to
   * traverse the list. New elements can be added to the list before or
   * after an existing element, at the head of the list, or at the end of
   * the list. A tail queue may be traversed in either direction.
   *
   * A circle queue is headed by a pair of pointers, one to the head of the
   * list and the other to the tail of the list. The elements are doubly
   * linked so that an arbitrary element can be removed without a need to
   * traverse the list. New elements can be added to the list before or after
   * an existing element, at the head of the list, or at the end of the list.
   * A circle queue may be traversed in either direction, but has a more
   * complex end of list detection.
   *
   * For details on the use of these macros, see the queue(3) manual page.
   *
   *
   *			SLIST	LIST	STAILQ	TAILQ	CIRCLEQ
   * _HEAD		+	+	+	+	+
   * _HEAD_INITIALIZER	+	+	+	+	+
   * _ENTRY		+	+	+	+	+
   * _INIT		+	+	+	+	+
   * _EMPTY		+	+	+	+	+
   * _FIRST		+	+	+	+	+
   * _NEXT		+	+	+	+	+
   * _PREV		-	-	-	+	+
   * _LAST		-	-	+	+	+
   * _FOREACH		+	+	+	+	+
   * _FOREACH_REVERSE	-	-	-	+	+
   * _INSERT_HEAD		+	+	+	+	+
   * _INSERT_BEFORE	-	+	-	+	+
   * _INSERT_AFTER	+	+	+	+	+
   * _INSERT_TAIL		-	-	+	+	+
   * _REMOVE_HEAD		+	-	+	-	-
   * _REMOVE		+	+	+	+	+
   *
   */
  
  /*
   * Singly-linked List declarations.
   */
  #define	SLIST_HEAD(name, type)						\
  struct name {								\
  	struct type *slh_first;	/* first element */			\
  }
  
  #define	SLIST_HEAD_INITIALIZER(head)					\
  	{ NULL }
   
  #define	SLIST_ENTRY(type)						\
  struct {								\
  	struct type *sle_next;	/* next element */			\
  }
   
  /*
   * Singly-linked List functions.
   */
  #define	SLIST_EMPTY(head)	((head)->slh_first == NULL)
  
  #define	SLIST_FIRST(head)	((head)->slh_first)
  
  #define	SLIST_FOREACH(var, head, field)					\
  	for ((var) = SLIST_FIRST((head));				\
  	    (var);							\
  	    (var) = SLIST_NEXT((var), field))
  
  #define	SLIST_INIT(head) do {						\
  	SLIST_FIRST((head)) = NULL;					\
  } while (0)
  
  #define	SLIST_INSERT_AFTER(slistelm, elm, field) do {			\
  	SLIST_NEXT((elm), field) = SLIST_NEXT((slistelm), field);	\
  	SLIST_NEXT((slistelm), field) = (elm);				\
  } while (0)
  
  #define	SLIST_INSERT_HEAD(head, elm, field) do {			\
  	SLIST_NEXT((elm), field) = SLIST_FIRST((head));			\
  	SLIST_FIRST((head)) = (elm);					\
  } while (0)
  
  #define	SLIST_NEXT(elm, field)	((elm)->field.sle_next)
  
  #define	SLIST_REMOVE(head, elm, type, field) do {			\
  	if (SLIST_FIRST((head)) == (elm)) {				\
  		SLIST_REMOVE_HEAD((head), field);			\
  	}								\
  	else {								\
  		struct type *curelm = SLIST_FIRST((head));		\
  		while (SLIST_NEXT(curelm, field) != (elm))		\
  			curelm = SLIST_NEXT(curelm, field);		\
  		SLIST_NEXT(curelm, field) =				\
  		    SLIST_NEXT(SLIST_NEXT(curelm, field), field);	\
  	}								\
  } while (0)
  
  #define	SLIST_REMOVE_HEAD(head, field) do {				\
  	SLIST_FIRST((head)) = SLIST_NEXT(SLIST_FIRST((head)), field);	\
  } while (0)
  
  /*
   * Singly-linked Tail queue declarations.
   */
  #define	STAILQ_HEAD(name, type)						\
  struct name {								\
  	struct type *stqh_first;/* first element */			\
  	struct type **stqh_last;/* addr of last next element */		\
  }
  
  #define	STAILQ_HEAD_INITIALIZER(head)					\
  	{ NULL, &(head).stqh_first }
  
  #define	STAILQ_ENTRY(type)						\
  struct {								\
  	struct type *stqe_next;	/* next element */			\
  }
  
  /*
   * Singly-linked Tail queue functions.
   */
  #define	STAILQ_EMPTY(head)	((head)->stqh_first == NULL)
  
  #define	STAILQ_FIRST(head)	((head)->stqh_first)
  
  #define	STAILQ_FOREACH(var, head, field)				\
  	for((var) = STAILQ_FIRST((head));				\
  	   (var);							\
  	   (var) = STAILQ_NEXT((var), field))
  
  #define	STAILQ_INIT(head) do {						\
  	STAILQ_FIRST((head)) = NULL;					\
  	(head)->stqh_last = &STAILQ_FIRST((head));			\
  } while (0)
  
  #define	STAILQ_INSERT_AFTER(head, tqelm, elm, field) do {		\
  	if ((STAILQ_NEXT((elm), field) = STAILQ_NEXT((tqelm), field)) == NULL)\
  		(head)->stqh_last = &STAILQ_NEXT((elm), field);		\
  	STAILQ_NEXT((tqelm), field) = (elm);				\
  } while (0)
  
  #define	STAILQ_INSERT_HEAD(head, elm, field) do {			\
  	if ((STAILQ_NEXT((elm), field) = STAILQ_FIRST((head))) == NULL)	\
  		(head)->stqh_last = &STAILQ_NEXT((elm), field);		\
  	STAILQ_FIRST((head)) = (elm);					\
  } while (0)
  
  #define	STAILQ_INSERT_TAIL(head, elm, field) do {			\
  	STAILQ_NEXT((elm), field) = NULL;				\
  	STAILQ_LAST((head)) = (elm);					\
  	(head)->stqh_last = &STAILQ_NEXT((elm), field);			\
  } while (0)
  
  #define	STAILQ_LAST(head)	(*(head)->stqh_last)
  
  #define	STAILQ_NEXT(elm, field)	((elm)->field.stqe_next)
  
  #define	STAILQ_REMOVE(head, elm, type, field) do {			\
  	if (STAILQ_FIRST((head)) == (elm)) {				\
  		STAILQ_REMOVE_HEAD(head, field);			\
  	}								\
  	else {								\
  		struct type *curelm = STAILQ_FIRST((head));		\
  		while (STAILQ_NEXT(curelm, field) != (elm))		\
  			curelm = STAILQ_NEXT(curelm, field);		\
  		if ((STAILQ_NEXT(curelm, field) =			\
  		     STAILQ_NEXT(STAILQ_NEXT(curelm, field), field)) == NULL)\
  			(head)->stqh_last = &STAILQ_NEXT((curelm), field);\
  	}								\
  } while (0)
  
  #define	STAILQ_REMOVE_HEAD(head, field) do {				\
  	if ((STAILQ_FIRST((head)) =					\
  	     STAILQ_NEXT(STAILQ_FIRST((head)), field)) == NULL)		\
  		(head)->stqh_last = &STAILQ_FIRST((head));		\
  } while (0)
  
  #define	STAILQ_REMOVE_HEAD_UNTIL(head, elm, field) do {			\
  	if ((STAILQ_FIRST((head)) = STAILQ_NEXT((elm), field)) == NULL)	\
  		(head)->stqh_last = &STAILQ_FIRST((head));		\
  } while (0)
  
  /*
   * List declarations.
   */
  #define	LIST_HEAD(name, type)						\
  struct name {								\
  	struct type *lh_first;	/* first element */			\
  }
  
  #define	LIST_HEAD_INITIALIZER(head)					\
  	{ NULL }
  
  #define	LIST_ENTRY(type)						\
  struct {								\
  	struct type *le_next;	/* next element */			\
  	struct type **le_prev;	/* address of previous next element */	\
  }
  
  /*
   * List functions.
   */
  
  #define	LIST_EMPTY(head)	((head)->lh_first == NULL)
  
  #define	LIST_FIRST(head)	((head)->lh_first)
  
  #define	LIST_FOREACH(var, head, field)					\
  	for ((var) = LIST_FIRST((head));				\
  	    (var);							\
  	    (var) = LIST_NEXT((var), field))
  
  #define	LIST_INIT(head) do {						\
  	LIST_FIRST((head)) = NULL;					\
  } while (0)
  
  #define	LIST_INSERT_AFTER(listelm, elm, field) do {			\
  	if ((LIST_NEXT((elm), field) = LIST_NEXT((listelm), field)) != NULL)\
  		LIST_NEXT((listelm), field)->field.le_prev =		\
  		    &LIST_NEXT((elm), field);				\
  	LIST_NEXT((listelm), field) = (elm);				\
  	(elm)->field.le_prev = &LIST_NEXT((listelm), field);		\
  } while (0)
  
  #define	LIST_INSERT_BEFORE(listelm, elm, field) do {			\
  	(elm)->field.le_prev = (listelm)->field.le_prev;		\
  	LIST_NEXT((elm), field) = (listelm);				\
  	*(listelm)->field.le_prev = (elm);				\
  	(listelm)->field.le_prev = &LIST_NEXT((elm), field);		\
  } while (0)
  
  #define	LIST_INSERT_HEAD(head, elm, field) do {				\
  	if ((LIST_NEXT((elm), field) = LIST_FIRST((head))) != NULL)	\
  		LIST_FIRST((head))->field.le_prev = &LIST_NEXT((elm), field);\
  	LIST_FIRST((head)) = (elm);					\
  	(elm)->field.le_prev = &LIST_FIRST((head));			\
  } while (0)
  
  #define	LIST_NEXT(elm, field)	((elm)->field.le_next)
  
  #define	LIST_REMOVE(elm, field) do {					\
  	if (LIST_NEXT((elm), field) != NULL)				\
  		LIST_NEXT((elm), field)->field.le_prev = 		\
  		    (elm)->field.le_prev;				\
  	*(elm)->field.le_prev = LIST_NEXT((elm), field);		\
  } while (0)
  
  /*
   * Tail queue declarations.
   */
  #define	TAILQ_HEAD(name, type)						\
  struct name {								\
  	struct type *tqh_first;	/* first element */			\
  	struct type **tqh_last;	/* addr of last next element */		\
  }
  
  #define	TAILQ_HEAD_INITIALIZER(head)					\
  	{ NULL, &(head).tqh_first }
  
  #define	TAILQ_ENTRY(type)						\
  struct {								\
  	struct type *tqe_next;	/* next element */			\
  	struct type **tqe_prev;	/* address of previous next element */	\
  }
  
  /*
   * Tail queue functions.
   */
  #define	TAILQ_EMPTY(head)	((head)->tqh_first == NULL)
  
  #define	TAILQ_FIRST(head)	((head)->tqh_first)
  
  #define	TAILQ_FOREACH(var, head, field)					\
  	for ((var) = TAILQ_FIRST((head));				\
  	    (var);							\
  	    (var) = TAILQ_NEXT((var), field))
  
  #define	TAILQ_FOREACH_REVERSE(var, head, headname, field)		\
  	for ((var) = TAILQ_LAST((head), headname);			\
  	    (var);							\
  	    (var) = TAILQ_PREV((var), headname, field))
  
  #define	TAILQ_INIT(head) do {						\
  	TAILQ_FIRST((head)) = NULL;					\
  	(head)->tqh_last = &TAILQ_FIRST((head));			\
  } while (0)
  
  #define	TAILQ_INSERT_AFTER(head, listelm, elm, field) do {		\
  	if ((TAILQ_NEXT((elm), field) = TAILQ_NEXT((listelm), field)) != NULL)\
  		TAILQ_NEXT((elm), field)->field.tqe_prev = 		\
  		    &TAILQ_NEXT((elm), field);				\
  	else								\
  		(head)->tqh_last = &TAILQ_NEXT((elm), field);		\
  	TAILQ_NEXT((listelm), field) = (elm);				\
  	(elm)->field.tqe_prev = &TAILQ_NEXT((listelm), field);		\
  } while (0)
  
  #define	TAILQ_INSERT_BEFORE(listelm, elm, field) do {			\
  	(elm)->field.tqe_prev = (listelm)->field.tqe_prev;		\
  	TAILQ_NEXT((elm), field) = (listelm);				\
  	*(listelm)->field.tqe_prev = (elm);				\
  	(listelm)->field.tqe_prev = &TAILQ_NEXT((elm), field);		\
  } while (0)
  
  #define	TAILQ_INSERT_HEAD(head, elm, field) do {			\
  	if ((TAILQ_NEXT((elm), field) = TAILQ_FIRST((head))) != NULL)	\
  		TAILQ_FIRST((head))->field.tqe_prev =			\
  		    &TAILQ_NEXT((elm), field);				\
  	else								\
  		(head)->tqh_last = &TAILQ_NEXT((elm), field);		\
  	TAILQ_FIRST((head)) = (elm);					\
  	(elm)->field.tqe_prev = &TAILQ_FIRST((head));			\
  } while (0)
  
  #define	TAILQ_INSERT_TAIL(head, elm, field) do {			\
  	TAILQ_NEXT((elm), field) = NULL;				\
  	(elm)->field.tqe_prev = (head)->tqh_last;			\
  	*(head)->tqh_last = (elm);					\
  	(head)->tqh_last = &TAILQ_NEXT((elm), field);			\
  } while (0)
  
  #define	TAILQ_LAST(head, headname)					\
  	(*(((struct headname *)((head)->tqh_last))->tqh_last))
  
  #define	TAILQ_NEXT(elm, field) ((elm)->field.tqe_next)
  
  #define	TAILQ_PREV(elm, headname, field)				\
  	(*(((struct headname *)((elm)->field.tqe_prev))->tqh_last))
  
  #define	TAILQ_REMOVE(head, elm, field) do {				\
  	if ((TAILQ_NEXT((elm), field)) != NULL)				\
  		TAILQ_NEXT((elm), field)->field.tqe_prev = 		\
  		    (elm)->field.tqe_prev;				\
  	else								\
  		(head)->tqh_last = (elm)->field.tqe_prev;		\
  	*(elm)->field.tqe_prev = TAILQ_NEXT((elm), field);		\
  } while (0)
  
  /*
   * Circular queue declarations.
   */
  #define	CIRCLEQ_HEAD(name, type)					\
  struct name {								\
  	struct type *cqh_first;		/* first element */		\
  	struct type *cqh_last;		/* last element */		\
  }
  
  #define	CIRCLEQ_HEAD_INITIALIZER(head)					\
  	{ (void *)&(head), (void *)&(head) }
  
  #define	CIRCLEQ_ENTRY(type)						\
  struct {								\
  	struct type *cqe_next;		/* next element */		\
  	struct type *cqe_prev;		/* previous element */		\
  }
  
  /*
   * Circular queue functions.
   */
  #define	CIRCLEQ_EMPTY(head)	((head)->cqh_first == (void *)(head))
  
  #define	CIRCLEQ_FIRST(head)	((head)->cqh_first)
  
  #define	CIRCLEQ_FOREACH(var, head, field)				\
  	for ((var) = CIRCLEQ_FIRST((head));				\
  	    (var) != (void *)(head);					\
  	    (var) = CIRCLEQ_NEXT((var), field))
  
  #define	CIRCLEQ_FOREACH_REVERSE(var, head, field)			\
  	for ((var) = CIRCLEQ_LAST((head));				\
  	    (var) != (void *)(head);					\
  	    (var) = CIRCLEQ_PREV((var), field))
  
  #define	CIRCLEQ_INIT(head) do {						\
  	CIRCLEQ_FIRST((head)) = (void *)(head);				\
  	CIRCLEQ_LAST((head)) = (void *)(head);				\
  } while (0)
  
  #define	CIRCLEQ_INSERT_AFTER(head, listelm, elm, field) do {		\
  	CIRCLEQ_NEXT((elm), field) = CIRCLEQ_NEXT((listelm), field);	\
  	CIRCLEQ_PREV((elm), field) = (listelm);				\
  	if (CIRCLEQ_NEXT((listelm), field) == (void *)(head))		\
  		CIRCLEQ_LAST((head)) = (elm);				\
  	else								\
  		CIRCLEQ_PREV(CIRCLEQ_NEXT((listelm), field), field) = (elm);\
  	CIRCLEQ_NEXT((listelm), field) = (elm);				\
  } while (0)
  
  #define	CIRCLEQ_INSERT_BEFORE(head, listelm, elm, field) do {		\
  	CIRCLEQ_NEXT((elm), field) = (listelm);				\
  	CIRCLEQ_PREV((elm), field) = CIRCLEQ_PREV((listelm), field);	\
  	if (CIRCLEQ_PREV((listelm), field) == (void *)(head))		\
  		CIRCLEQ_FIRST((head)) = (elm);				\
  	else								\
  		CIRCLEQ_NEXT(CIRCLEQ_PREV((listelm), field), field) = (elm);\
  	CIRCLEQ_PREV((listelm), field) = (elm);				\
  } while (0)
  
  #define	CIRCLEQ_INSERT_HEAD(head, elm, field) do {			\
  	CIRCLEQ_NEXT((elm), field) = CIRCLEQ_FIRST((head));		\
  	CIRCLEQ_PREV((elm), field) = (void *)(head);			\
  	if (CIRCLEQ_LAST((head)) == (void *)(head))			\
  		CIRCLEQ_LAST((head)) = (elm);				\
  	else								\
  		CIRCLEQ_PREV(CIRCLEQ_FIRST((head)), field) = (elm);	\
  	CIRCLEQ_FIRST((head)) = (elm);					\
  } while (0)
  
  #define	CIRCLEQ_INSERT_TAIL(head, elm, field) do {			\
  	CIRCLEQ_NEXT((elm), field) = (void *)(head);			\
  	CIRCLEQ_PREV((elm), field) = CIRCLEQ_LAST((head));		\
  	if (CIRCLEQ_FIRST((head)) == (void *)(head))			\
  		CIRCLEQ_FIRST((head)) = (elm);				\
  	else								\
  		CIRCLEQ_NEXT(CIRCLEQ_LAST((head)), field) = (elm);	\
  	CIRCLEQ_LAST((head)) = (elm);					\
  } while (0)
  
  #define	CIRCLEQ_LAST(head)	((head)->cqh_last)
  
  #define	CIRCLEQ_NEXT(elm,field)	((elm)->field.cqe_next)
  
  #define	CIRCLEQ_PREV(elm,field)	((elm)->field.cqe_prev)
  
  #define	CIRCLEQ_REMOVE(head, elm, field) do {				\
  	if (CIRCLEQ_NEXT((elm), field) == (void *)(head))		\
  		CIRCLEQ_LAST((head)) = CIRCLEQ_PREV((elm), field);	\
  	else								\
  		CIRCLEQ_PREV(CIRCLEQ_NEXT((elm), field), field) =	\
  		    CIRCLEQ_PREV((elm), field);				\
  	if (CIRCLEQ_PREV((elm), field) == (void *)(head))		\
  		CIRCLEQ_FIRST((head)) = CIRCLEQ_NEXT((elm), field);	\
  	else								\
  		CIRCLEQ_NEXT(CIRCLEQ_PREV((elm), field), field) =	\
  		    CIRCLEQ_NEXT((elm), field);				\
  } while (0)
  
  #endif /* !_SYS_QUEUE_H_ */