msullivan/variable_queue.h

## variable_queue.h
/**
 * @file variable_queue.h
 *
 * @brief Generalized queue module for data collection
 *
 * @author Michael Sullivan (sully@msully.net)
 **/

#include <stddef.h>
#include <stdlib.h>
#include <assert.h>

/* This is probably all sorts of undefined behavior but seriously fuck off. */
#define VQ_OFF_LIST ((void*)~0)

/**
 * @def Q_NEW_HEAD(Q_HEAD_TYPE, Q_ELEM_TYPE)
 *
 *  @brief Generates a new structure of type Q_HEAD_TYPE representing the head
 *  of a queue of elements of type Q_ELEM_TYPE.
 *
 *  Usage: Q_NEW_HEAD(Q_HEAD_TYPE, Q_ELEM_TYPE); //create the type <br>
 *         Q_HEAD_TYPE headName; //instantiate a head of the given type
 *
 *  @param Q_HEAD_TYPE the type you wish the newly-generated structure to have.
 *
 *  @param Q_ELEM_TYPE the type of elements stored in the queue.
 *         Q_ELEM_TYPE must be a structure.
 *
 **/

#define Q_NEW_HEAD(Q_HEAD_TYPE, Q_ELEM_TYPE) \
	typedef struct Q_HEAD_TYPE {             \
		struct Q_ELEM_TYPE *head;            \
		struct Q_ELEM_TYPE *tail;            \
		size_t count;                        \
	} Q_HEAD_TYPE

/**
 * @def Q_HEAD_INITIALIZER
 * @brief A static initializer for a queue's head
 */
#define Q_HEAD_INITIALIZER {NULL, NULL, 0}
#define Q_HEAD_INIT Q_HEAD_INITIALIZER

/**
 * @def Q_NEW_LINK(Q_ELEM_TYPE)
 *
 *  @brief Instantiates a link within a structure, allowing that structure to be
 *         collected into a queue created with Q_NEW_HEAD.
 *
 *  Usage: <br>
 *  typedef struct Q_ELEM_TYPE {<br>
 *  Q_NEW_LINK(Q_ELEM_TYPE) LINK_NAME; //instantiate the link <br>
 *  } Q_ELEM_TYPE; <br>
 *
 *  A structure can have more than one link defined within it, as long as they
 *  have different names. This allows the structure to be placed in more than
 *  one queue simultanteously.
 *
 *  @param Q_ELEM_TYPE the type of the structure containing the link
 **/
#define Q_NEW_LINK(Q_ELEM_TYPE)          \
	struct {                             \
		struct Q_ELEM_TYPE *next;        \
		struct Q_ELEM_TYPE *prev;        \
	}

/**
 * @def Q_INIT_HEAD(Q_HEAD)
 *
 *  @brief Initializes the head of a queue so that the queue head can be used
 *         properly.
 *  @param Q_HEAD Pointer to queue head to initialize
 **/
#define Q_INIT_HEAD(Q_HEAD) do {                \
		(Q_HEAD)->head = (Q_HEAD)->tail = NULL; \
		(Q_HEAD)->count = 0;                    \
	} while (0)

/**
 * @def Q_LINK_INITIALIZER
 * @brief A static initializer for a link
 */
#define Q_LINK_INITIALIZER {VQ_OFF_LIST, VQ_OFF_LIST}
#define Q_LINK_INIT Q_LINK_INITIALIZER

/**
 * @def Q_INIT_ELEM(Q_ELEM, LINK_NAME)
 *
 *  @brief Initializes the link named LINK_NAME in an instance of the structure
 *         Q_ELEM.
 *
 *  Once initialized, the link can be used to organized elements in a queue.
 *
 *  @param Q_ELEM Pointer to the structure instance containing the link
 *  @param LINK_NAME The name of the link to initialize
 **/
#define Q_INIT_ELEM(Q_ELEM, LINK_NAME) do { \
		(Q_ELEM)->LINK_NAME.next = VQ_OFF_LIST; \
		(Q_ELEM)->LINK_NAME.prev = VQ_OFF_LIST; \
	} while (0)

#define Q_IN_LIST(Q_HEAD, Q_ELEM, LINK_NAME) (                          \
		(((Q_ELEM)->LINK_NAME.prev &&                                   \
		  (Q_ELEM)->LINK_NAME.prev->LINK_NAME.next == (Q_ELEM)) ||      \
		 (!(Q_ELEM)->LINK_NAME.prev &&                                  \
		  (Q_HEAD)->head == (Q_ELEM))) &&                               \
		(((Q_ELEM)->LINK_NAME.next &&                                   \
		  (Q_ELEM)->LINK_NAME.next->LINK_NAME.prev == (Q_ELEM)) ||      \
		 (!(Q_ELEM)->LINK_NAME.next &&                                  \
		  (Q_HEAD)->tail == (Q_ELEM)))                                  \
		)

#define Q_ASSERT_CONSISTENT(Q_HEAD, Q_ELEM, LINK_NAME) \
	assert(Q_IN_LIST((Q_HEAD), (Q_ELEM), LINK_NAME))

#define Q_ON_LIST(Q_ELEM, LINK_NAME) \
	((Q_ELEM)->LINK_NAME.next != VQ_OFF_LIST && \
	 (Q_ELEM)->LINK_NAME.prev != VQ_OFF_LIST)


#define Q_ASSERT_LINK(Q_ELEM, LINK_NAME) \
	assert(!Q_ON_LIST(Q_ELEM, LINK_NAME))

/**
 * @def Q_INSERT_FRONT(Q_HEAD, Q_ELEM, LINK_NAME)
 *
 *  @brief Inserts the queue element pointed to by Q_ELEM at the front of the
 *         queue headed by the structure Q_HEAD.
 *
 *  The link identified by LINK_NAME will be used to organize the element and
 *  record its location in the queue.
 *
 *  @param Q_HEAD Pointer to the head of the queue into which Q_ELEM will be
 *         inserted
 *  @param Q_ELEM Pointer to the element to insert into the queue
 *  @param LINK_NAME Name of the link used to organize the queue
 *
 *  @return Void
 **/
#define Q_INSERT_FRONT(Q_HEAD, Q_ELEM, LINK_NAME) do {  \
		Q_ASSERT_LINK(Q_ELEM, LINK_NAME);               \
		(Q_ELEM)->LINK_NAME.prev = NULL;                \
		(Q_ELEM)->LINK_NAME.next = (Q_HEAD)->head;      \
		if ((Q_HEAD)->head)                             \
			(Q_HEAD)->head->LINK_NAME.prev = (Q_ELEM);  \
		(Q_HEAD)->head = (Q_ELEM);                      \
		if (!(Q_HEAD)->tail)                            \
			(Q_HEAD)->tail = (Q_ELEM);                  \
		(Q_HEAD)->count++;                              \
		                                                \
		Q_ASSERT_CONSISTENT(Q_HEAD, Q_ELEM, LINK_NAME); \
	} while (0)
#define Q_INSERT_HEAD Q_INSERT_FRONT

/**
 *  @def Q_INSERT_TAIL(Q_HEAD, Q_ELEM, LINK_NAME)
 *  @brief Inserts the queue element pointed to by Q_ELEM at the end of the
 *         queue headed by the structure pointed to by Q_HEAD.
 *
 *  The link identified by LINK_NAME will be used to organize the element and
 *  record its location in the queue.
 *
 *  @param Q_HEAD Pointer to the head of the queue into which Q_ELEM will be
 *         inserted
 *  @param Q_ELEM Pointer to the element to insert into the queue
 *  @param LINK_NAME Name of the link used to organize the queue
 *
 *  @return Void
 **/
#define Q_INSERT_TAIL(Q_HEAD, Q_ELEM, LINK_NAME) do {   \
		Q_ASSERT_LINK(Q_ELEM, LINK_NAME);               \
		(Q_ELEM)->LINK_NAME.next = NULL;                \
		(Q_ELEM)->LINK_NAME.prev = (Q_HEAD)->tail;      \
		if ((Q_HEAD)->tail)                             \
			(Q_HEAD)->tail->LINK_NAME.next = (Q_ELEM);  \
		(Q_HEAD)->tail = (Q_ELEM);					  	\
		if (!(Q_HEAD)->head)							\
			(Q_HEAD)->head = (Q_ELEM);					\
		(Q_HEAD)->count++;                              \
		                                                \
		Q_ASSERT_CONSISTENT(Q_HEAD, Q_ELEM, LINK_NAME); \
	} while (0)

/**
 * @def Q_GET_SIZE(Q_HEAD)
 *
 * @brief Returns the number of elements in the queue.
 *
 * @param Q_HEAD Pointer to the head of the queue
 * @return The number of elements in the queue
 */
#define Q_GET_SIZE(Q_HEAD) (Q_HEAD)->count

/**
 * @def Q_GET_FRONT(Q_HEAD)
 *
 *  @brief Returns a pointer to the first element in the queue, or NULL
 *  (memory address 0) if the queue is empty.
 *
 *  @param Q_HEAD Pointer to the head of the queue
 *  @return Pointer to the first element in the queue, or NULL if the queue
 *          is empty
 **/
#define Q_GET_FRONT(Q_HEAD) (Q_HEAD)->head
#define Q_GET_HEAD Q_GET_FRONT

/**
 * @def Q_GET_TAIL(Q_HEAD)
 *
 *  @brief Returns a pointer to the last element in the queue, or NULL
 *  (memory address 0) if the queue is empty.
 *
 *  @param Q_HEAD Pointer to the head of the queue
 *  @return Pointer to the last element in the queue, or NULL if the queue
 *          is empty
 **/
#define Q_GET_TAIL(Q_HEAD) (Q_HEAD)->tail

/**
 * @def Q_GET_NEXT(Q_ELEM, LINK_NAME)
 *
 *  @brief Returns a pointer to the next element in the queue, as linked to by
 *         the link specified with LINK_NAME.
 *
 *  If Q_ELEM is not in a queue or is the last element in the queue,
 *  Q_GET_NEXT should return NULL.
 *
 *  @param Q_ELEM Pointer to the queue element before the desired element
 *  @param LINK_NAME Name of the link organizing the queue
 *
 *  @return The element after Q_ELEM, or NULL if there is no next element
 **/
#define Q_GET_NEXT(Q_ELEM, LINK_NAME) (Q_ELEM)->LINK_NAME.next

/**
 * @def Q_GET_PREV(Q_ELEM, LINK_NAME)
 *
 *  @brief Returns a pointer to the previous element in the queue, as linked to
 *         by the link specified with LINK_NAME.
 *
 *  If Q_ELEM is not in a queue or is the first element in the queue,
 *  Q_GET_NEXT should return NULL.
 *
 *  @param Q_ELEM Pointer to the queue element after the desired element
 *  @param LINK_NAME Name of the link organizing the queue
 *
 *  @return The element before Q_ELEM, or NULL if there is no next element
 **/
#define Q_GET_PREV(Q_ELEM, LINK_NAME) (Q_ELEM)->LINK_NAME.prev

/**
 * @def Q_INSERT_AFTER(Q_HEAD, Q_INQ, Q_TOINSERT, LINK_NAME)
 *
 *  @brief Inserts the queue element Q_TOINSERT after the element Q_INQ
 *         in the queue.
 *
 *  Inserts an element into a queue after a given element. If the given
 *  element is the last element, Q_HEAD should be updated appropriately
 *  (so that Q_TOINSERT becomes the tail element)
 *
 *  @param Q_HEAD head of the queue into which Q_TOINSERT will be inserted
 *  @param Q_INQ  Element already in the queue
 *  @param Q_TOINSERT Element to insert into queue
 *  @param LINK_NAME  Name of link field used to organize the queue
 **/
#define Q_INSERT_AFTER(Q_HEAD,Q_INQ,Q_TOINSERT,LINK_NAME) do {    \
		Q_ASSERT_LINK(Q_TOINSERT, LINK_NAME);                     \
		Q_ASSERT_CONSISTENT(Q_HEAD, Q_INQ, LINK_NAME);            \
		                                                          \
		(Q_TOINSERT)->LINK_NAME.prev = (Q_INQ);                   \
		(Q_TOINSERT)->LINK_NAME.next = (Q_INQ)->LINK_NAME.next;   \
		if ((Q_INQ)->LINK_NAME.next)                              \
			(Q_INQ)->LINK_NAME.next->LINK_NAME.prev = Q_TOINSERT; \
		(Q_INQ)->LINK_NAME.next = (Q_TOINSERT);                   \
		if ((Q_INQ) == (Q_HEAD)->tail)                            \
			(Q_HEAD)->tail = (Q_TOINSERT);                        \
		(Q_HEAD)->count++;                                        \
		                                                          \
		Q_ASSERT_CONSISTENT(Q_HEAD, Q_TOINSERT, LINK_NAME);       \
	} while (0)

/**
 * @def Q_INSERT_BEFORE(Q_HEAD, Q_INQ, Q_TOINSERT, LINK_NAME)
 *
 *  @brief Inserts the queue element Q_TOINSERT before the element Q_INQ
 *         in the queue.
 *
 *  Inserts an element into a queue before a given element. If the given
 *  element is the first element, Q_HEAD should be updated appropriately
 *  (so that Q_TOINSERT becomes the front element)
 *
 *  @param Q_HEAD head of the queue into which Q_TOINSERT will be inserted
 *  @param Q_INQ  Element already in the queue
 *  @param Q_TOINSERT Element to insert into queue
 *  @param LINK_NAME  Name of link field used to organize the queue
 **/
#define Q_INSERT_BEFORE(Q_HEAD,Q_INQ,Q_TOINSERT,LINK_NAME) do {   \
		Q_ASSERT_LINK(Q_TOINSERT, LINK_NAME);                     \
		Q_ASSERT_CONSISTENT(Q_HEAD, Q_INQ, LINK_NAME);            \
		                                                          \
		(Q_TOINSERT)->LINK_NAME.next = (Q_INQ);                   \
		(Q_TOINSERT)->LINK_NAME.prev = (Q_INQ)->LINK_NAME.prev;   \
		if ((Q_INQ)->LINK_NAME.prev)                              \
			(Q_INQ)->LINK_NAME.prev->LINK_NAME.next = Q_TOINSERT; \
		(Q_INQ)->LINK_NAME.prev = (Q_TOINSERT);                   \
		if ((Q_INQ) == (Q_HEAD)->head)                            \
			(Q_HEAD)->head = (Q_TOINSERT);                        \
		(Q_HEAD)->count++;                                        \
		                                                          \
		Q_ASSERT_CONSISTENT(Q_HEAD, Q_TOINSERT, LINK_NAME);       \
	} while (0)

/**
 * @def Q_REMOVE(Q_HEAD,Q_ELEM,LINK_NAME)
 *
 *  @brief Detaches the element Q_ELEM from the queue organized by LINK_NAME,
 *         and returns a pointer to the element.
 *
 *  If Q_HEAD does not use the link named LINK_NAME to organize its elements
 *  the behavior of this macro is undefined.
 *
 *  @param Q_HEAD Pointer to the head of the queue containing Q_ELEM. If
 *         Q_REMOVE removes the first, last, or only element in the queue,
 *         Q_HEAD should be updated appropriately.
 *  @param Q_ELEM Pointer to the element to remove from the queue headed by
 *         Q_HEAD.
 *  @param LINK_NAME The name of the link used to organize Q_HEAD's queue
 *
 *  @return Void
 **/
#define Q_REMOVE(Q_HEAD,Q_ELEM,LINK_NAME) do {                          \
		Q_ASSERT_CONSISTENT(Q_HEAD, Q_ELEM, LINK_NAME);                 \
		if ((Q_ELEM)->LINK_NAME.prev)                                   \
			(Q_ELEM)->LINK_NAME.prev->LINK_NAME.next=(Q_ELEM)->LINK_NAME.next; \
		if ((Q_ELEM)->LINK_NAME.next)                                   \
			(Q_ELEM)->LINK_NAME.next->LINK_NAME.prev=(Q_ELEM)->LINK_NAME.prev; \
		if ((Q_ELEM) == (Q_HEAD)->head)                                 \
			(Q_HEAD)->head = (Q_ELEM)->LINK_NAME.next;                  \
		if ((Q_ELEM) == (Q_HEAD)->tail)                                 \
			(Q_HEAD)->tail = (Q_ELEM)->LINK_NAME.prev;                  \
		(Q_HEAD)->count--;                                              \
		(Q_ELEM)->LINK_NAME.next = VQ_OFF_LIST;                         \
		(Q_ELEM)->LINK_NAME.prev = VQ_OFF_LIST;                         \
	} while (0)

/**
 * @def Q_CONCAT(Q_HEAD1,Q_HEAD2,LINK_NAME)
 *
 * @brief Concatenates two lists together
 *  @param Q_HEAD1 The first list
 *  @param Q_HEAD2 The second list
 *  @param LINK_NAME The name of the link used to organize Q_HEAD's queue
 *
 *  @return Void
 **/
#define Q_CONCAT(Q_HEAD1,Q_HEAD2,LINK_NAME) do {                        \
		if (!(Q_HEAD1)->head) {                                         \
			*(Q_HEAD1) = *(Q_HEAD2);									\
		} else if ((Q_HEAD2)->head) {									\
			(Q_HEAD1)->tail->LINK_NAME.next = (Q_HEAD2)->head;			\
			(Q_HEAD2)->head->LINK_NAME.prev = (Q_HEAD1)->tail;			\
			(Q_HEAD1)->tail = (Q_HEAD2)->tail;							\
			(Q_HEAD1)->count += (Q_HEAD2)->count;						\
		}																\
		(Q_HEAD2)->head = (Q_HEAD2)->tail = NULL;						\
		(Q_HEAD2)->count = 0;											\
	} while (0)


/**
 * @def Q_FOREACH(CURRENT_ELEM,Q_HEAD,LINK_NAME)
 *
 *  @brief Constructs an iterator block (like a for block) that operates
 *         on each element in Q_HEAD, in order.
 *
 *  Q_FOREACH constructs the head of a block of code that will iterate through
 *  each element in the queue headed by Q_HEAD. Each time through the loop,
 *  the variable named by CURRENT_ELEM will be set to point to a subsequent
 *  element in the queue.
 *
 *  Usage:<br>
 *  Q_FOREACH(CURRENT_ELEM,Q_HEAD,LINK_NAME)<br>
 *  {<br>
 *  ... operate on the variable CURRENT_ELEM ... <br>
 *  }
 *
 *  If LINK_NAME is not used to organize the queue headed by Q_HEAD, then
 *  the behavior of this macro is undefined.
 *
 *  @param CURRENT_ELEM name of the variable to use for iteration. On each
 *         loop through the Q_FOREACH block, CURRENT_ELEM will point to the
 *         current element in the queue. CURRENT_ELEM should be an already-
 *         defined variable name, and its type should be a pointer to
 *         the type of data organized by Q_HEAD
 *  @param Q_HEAD Pointer to the head of the queue to iterate through
 *  @param LINK_NAME The name of the link used to organize the queue headed
 *         by Q_HEAD.
 **/
#define Q_FOREACH(CURRENT_ELEM,Q_HEAD,LINK_NAME)            \
	for ((CURRENT_ELEM) = (Q_HEAD)->head; (CURRENT_ELEM);   \
		 (CURRENT_ELEM) = (CURRENT_ELEM)->LINK_NAME.next)

/**
 * @def Q_SEARCH(OUTPUT,Q_HEAD,LINK_NAME,EXPR)
 *
 * @brief Searches each element in Q_HEAD for a node that satisfies
 * EXPR.
 *
 * @param OUTPUT name of the variable to use in the iteration. If a
 *        node that satisfies EXPR is found, iteration is stopped and OUTPUT
 *        is set as that value. If no node that satisfies EXPR is found,
 *        OUTPUT will be NULL. In EXPR, OUTPUT will point the the current
 *        node.
 *  @param Q_HEAD Pointer to the head of the queue to iterate through
 *  @param LINK_NAME The name of the link used to organize the queue headed
 *         by Q_HEAD.
 *  @param EXPR An expression that evaluates true when the wanted
 *         element is seen
 **/
#define Q_SEARCH(OUTPUT,Q_HEAD,LINK_NAME,EXPR)      \
	do {                                            \
		Q_FOREACH((OUTPUT),(Q_HEAD),LINK_NAME) {    \
			if ((EXPR)) {                           \
				break;                              \
			}                                       \
		}                                           \
	} while (0)
	/**
	* @file variable_queue.h
	*
	* @brief Generalized queue module for data collection
	*
	* @author Michael Sullivan (sully@msully.net)
	**/

	#include <stddef.h>
	#include <stdlib.h>
	#include <assert.h>

	/* This is probably all sorts of undefined behavior but seriously fuck off. */
	#define VQ_OFF_LIST ((void*)~0)

	/**
	* @def Q_NEW_HEAD(Q_HEAD_TYPE, Q_ELEM_TYPE)
	*
	* @brief Generates a new structure of type Q_HEAD_TYPE representing the head
	* of a queue of elements of type Q_ELEM_TYPE.
	*
	* Usage: Q_NEW_HEAD(Q_HEAD_TYPE, Q_ELEM_TYPE); //create the type <br>
	* Q_HEAD_TYPE headName; //instantiate a head of the given type
	*
	* @param Q_HEAD_TYPE the type you wish the newly-generated structure to have.
	*
	* @param Q_ELEM_TYPE the type of elements stored in the queue.
	* Q_ELEM_TYPE must be a structure.
	*
	**/

	#define Q_NEW_HEAD(Q_HEAD_TYPE, Q_ELEM_TYPE) \
	typedef struct Q_HEAD_TYPE { \
	struct Q_ELEM_TYPE *head; \
	struct Q_ELEM_TYPE *tail; \
	size_t count; \
	} Q_HEAD_TYPE

	/**
	* @def Q_HEAD_INITIALIZER
	* @brief A static initializer for a queue's head
	*/
	#define Q_HEAD_INITIALIZER {NULL, NULL, 0}
	#define Q_HEAD_INIT Q_HEAD_INITIALIZER

	/**
	* @def Q_NEW_LINK(Q_ELEM_TYPE)
	*
	* @brief Instantiates a link within a structure, allowing that structure to be
	* collected into a queue created with Q_NEW_HEAD.
	*
	* Usage: <br>
	* typedef struct Q_ELEM_TYPE {<br>
	* Q_NEW_LINK(Q_ELEM_TYPE) LINK_NAME; //instantiate the link <br>
	* } Q_ELEM_TYPE; <br>
	*
	* A structure can have more than one link defined within it, as long as they
	* have different names. This allows the structure to be placed in more than
	* one queue simultanteously.
	*
	* @param Q_ELEM_TYPE the type of the structure containing the link
	**/
	#define Q_NEW_LINK(Q_ELEM_TYPE) \
	struct { \
	struct Q_ELEM_TYPE *next; \
	struct Q_ELEM_TYPE *prev; \
	}

	/**
	* @def Q_INIT_HEAD(Q_HEAD)
	*
	* @brief Initializes the head of a queue so that the queue head can be used
	* properly.
	* @param Q_HEAD Pointer to queue head to initialize
	**/
	#define Q_INIT_HEAD(Q_HEAD) do { \
	(Q_HEAD)->head = (Q_HEAD)->tail = NULL; \
	(Q_HEAD)->count = 0; \
	} while (0)

	/**
	* @def Q_LINK_INITIALIZER
	* @brief A static initializer for a link
	*/
	#define Q_LINK_INITIALIZER {VQ_OFF_LIST, VQ_OFF_LIST}
	#define Q_LINK_INIT Q_LINK_INITIALIZER

	/**
	* @def Q_INIT_ELEM(Q_ELEM, LINK_NAME)
	*
	* @brief Initializes the link named LINK_NAME in an instance of the structure
	* Q_ELEM.
	*
	* Once initialized, the link can be used to organized elements in a queue.
	*
	* @param Q_ELEM Pointer to the structure instance containing the link
	* @param LINK_NAME The name of the link to initialize
	**/
	#define Q_INIT_ELEM(Q_ELEM, LINK_NAME) do { \
	(Q_ELEM)->LINK_NAME.next = VQ_OFF_LIST; \
	(Q_ELEM)->LINK_NAME.prev = VQ_OFF_LIST; \
	} while (0)

	#define Q_IN_LIST(Q_HEAD, Q_ELEM, LINK_NAME) ( \
	(((Q_ELEM)->LINK_NAME.prev && \
	(Q_ELEM)->LINK_NAME.prev->LINK_NAME.next == (Q_ELEM)) \|\| \
	(!(Q_ELEM)->LINK_NAME.prev && \
	(Q_HEAD)->head == (Q_ELEM))) && \
	(((Q_ELEM)->LINK_NAME.next && \
	(Q_ELEM)->LINK_NAME.next->LINK_NAME.prev == (Q_ELEM)) \|\| \
	(!(Q_ELEM)->LINK_NAME.next && \
	(Q_HEAD)->tail == (Q_ELEM))) \
	)

	#define Q_ASSERT_CONSISTENT(Q_HEAD, Q_ELEM, LINK_NAME) \
	assert(Q_IN_LIST((Q_HEAD), (Q_ELEM), LINK_NAME))

	#define Q_ON_LIST(Q_ELEM, LINK_NAME) \
	((Q_ELEM)->LINK_NAME.next != VQ_OFF_LIST && \
	(Q_ELEM)->LINK_NAME.prev != VQ_OFF_LIST)


	#define Q_ASSERT_LINK(Q_ELEM, LINK_NAME) \
	assert(!Q_ON_LIST(Q_ELEM, LINK_NAME))

	/**
	* @def Q_INSERT_FRONT(Q_HEAD, Q_ELEM, LINK_NAME)
	*
	* @brief Inserts the queue element pointed to by Q_ELEM at the front of the
	* queue headed by the structure Q_HEAD.
	*
	* The link identified by LINK_NAME will be used to organize the element and
	* record its location in the queue.
	*
	* @param Q_HEAD Pointer to the head of the queue into which Q_ELEM will be
	* inserted
	* @param Q_ELEM Pointer to the element to insert into the queue
	* @param LINK_NAME Name of the link used to organize the queue
	*
	* @return Void
	**/
	#define Q_INSERT_FRONT(Q_HEAD, Q_ELEM, LINK_NAME) do { \
	Q_ASSERT_LINK(Q_ELEM, LINK_NAME); \
	(Q_ELEM)->LINK_NAME.prev = NULL; \
	(Q_ELEM)->LINK_NAME.next = (Q_HEAD)->head; \
	if ((Q_HEAD)->head) \
	(Q_HEAD)->head->LINK_NAME.prev = (Q_ELEM); \
	(Q_HEAD)->head = (Q_ELEM); \
	if (!(Q_HEAD)->tail) \
	(Q_HEAD)->tail = (Q_ELEM); \
	(Q_HEAD)->count++; \
	\
	Q_ASSERT_CONSISTENT(Q_HEAD, Q_ELEM, LINK_NAME); \
	} while (0)
	#define Q_INSERT_HEAD Q_INSERT_FRONT

	/**
	* @def Q_INSERT_TAIL(Q_HEAD, Q_ELEM, LINK_NAME)
	* @brief Inserts the queue element pointed to by Q_ELEM at the end of the
	* queue headed by the structure pointed to by Q_HEAD.
	*
	* The link identified by LINK_NAME will be used to organize the element and
	* record its location in the queue.
	*
	* @param Q_HEAD Pointer to the head of the queue into which Q_ELEM will be
	* inserted
	* @param Q_ELEM Pointer to the element to insert into the queue
	* @param LINK_NAME Name of the link used to organize the queue
	*
	* @return Void
	**/
	#define Q_INSERT_TAIL(Q_HEAD, Q_ELEM, LINK_NAME) do { \
	Q_ASSERT_LINK(Q_ELEM, LINK_NAME); \
	(Q_ELEM)->LINK_NAME.next = NULL; \
	(Q_ELEM)->LINK_NAME.prev = (Q_HEAD)->tail; \
	if ((Q_HEAD)->tail) \
	(Q_HEAD)->tail->LINK_NAME.next = (Q_ELEM); \
	(Q_HEAD)->tail = (Q_ELEM); \
	if (!(Q_HEAD)->head) \
	(Q_HEAD)->head = (Q_ELEM); \
	(Q_HEAD)->count++; \
	\
	Q_ASSERT_CONSISTENT(Q_HEAD, Q_ELEM, LINK_NAME); \
	} while (0)

	/**
	* @def Q_GET_SIZE(Q_HEAD)
	*
	* @brief Returns the number of elements in the queue.
	*
	* @param Q_HEAD Pointer to the head of the queue
	* @return The number of elements in the queue
	*/
	#define Q_GET_SIZE(Q_HEAD) (Q_HEAD)->count

	/**
	* @def Q_GET_FRONT(Q_HEAD)
	*
	* @brief Returns a pointer to the first element in the queue, or NULL
	* (memory address 0) if the queue is empty.
	*
	* @param Q_HEAD Pointer to the head of the queue
	* @return Pointer to the first element in the queue, or NULL if the queue
	* is empty
	**/
	#define Q_GET_FRONT(Q_HEAD) (Q_HEAD)->head
	#define Q_GET_HEAD Q_GET_FRONT

	/**
	* @def Q_GET_TAIL(Q_HEAD)
	*
	* @brief Returns a pointer to the last element in the queue, or NULL
	* (memory address 0) if the queue is empty.
	*
	* @param Q_HEAD Pointer to the head of the queue
	* @return Pointer to the last element in the queue, or NULL if the queue
	* is empty
	**/
	#define Q_GET_TAIL(Q_HEAD) (Q_HEAD)->tail

	/**
	* @def Q_GET_NEXT(Q_ELEM, LINK_NAME)
	*
	* @brief Returns a pointer to the next element in the queue, as linked to by
	* the link specified with LINK_NAME.
	*
	* If Q_ELEM is not in a queue or is the last element in the queue,
	* Q_GET_NEXT should return NULL.
	*
	* @param Q_ELEM Pointer to the queue element before the desired element
	* @param LINK_NAME Name of the link organizing the queue
	*
	* @return The element after Q_ELEM, or NULL if there is no next element
	**/
	#define Q_GET_NEXT(Q_ELEM, LINK_NAME) (Q_ELEM)->LINK_NAME.next

	/**
	* @def Q_GET_PREV(Q_ELEM, LINK_NAME)
	*
	* @brief Returns a pointer to the previous element in the queue, as linked to
	* by the link specified with LINK_NAME.
	*
	* If Q_ELEM is not in a queue or is the first element in the queue,
	* Q_GET_NEXT should return NULL.
	*
	* @param Q_ELEM Pointer to the queue element after the desired element
	* @param LINK_NAME Name of the link organizing the queue
	*
	* @return The element before Q_ELEM, or NULL if there is no next element
	**/
	#define Q_GET_PREV(Q_ELEM, LINK_NAME) (Q_ELEM)->LINK_NAME.prev

	/**
	* @def Q_INSERT_AFTER(Q_HEAD, Q_INQ, Q_TOINSERT, LINK_NAME)
	*
	* @brief Inserts the queue element Q_TOINSERT after the element Q_INQ
	* in the queue.
	*
	* Inserts an element into a queue after a given element. If the given
	* element is the last element, Q_HEAD should be updated appropriately
	* (so that Q_TOINSERT becomes the tail element)
	*
	* @param Q_HEAD head of the queue into which Q_TOINSERT will be inserted
	* @param Q_INQ Element already in the queue
	* @param Q_TOINSERT Element to insert into queue
	* @param LINK_NAME Name of link field used to organize the queue
	**/
	#define Q_INSERT_AFTER(Q_HEAD,Q_INQ,Q_TOINSERT,LINK_NAME) do { \
	Q_ASSERT_LINK(Q_TOINSERT, LINK_NAME); \
	Q_ASSERT_CONSISTENT(Q_HEAD, Q_INQ, LINK_NAME); \
	\
	(Q_TOINSERT)->LINK_NAME.prev = (Q_INQ); \
	(Q_TOINSERT)->LINK_NAME.next = (Q_INQ)->LINK_NAME.next; \
	if ((Q_INQ)->LINK_NAME.next) \
	(Q_INQ)->LINK_NAME.next->LINK_NAME.prev = Q_TOINSERT; \
	(Q_INQ)->LINK_NAME.next = (Q_TOINSERT); \
	if ((Q_INQ) == (Q_HEAD)->tail) \
	(Q_HEAD)->tail = (Q_TOINSERT); \
	(Q_HEAD)->count++; \
	\
	Q_ASSERT_CONSISTENT(Q_HEAD, Q_TOINSERT, LINK_NAME); \
	} while (0)

	/**
	* @def Q_INSERT_BEFORE(Q_HEAD, Q_INQ, Q_TOINSERT, LINK_NAME)
	*
	* @brief Inserts the queue element Q_TOINSERT before the element Q_INQ
	* in the queue.
	*
	* Inserts an element into a queue before a given element. If the given
	* element is the first element, Q_HEAD should be updated appropriately
	* (so that Q_TOINSERT becomes the front element)
	*
	* @param Q_HEAD head of the queue into which Q_TOINSERT will be inserted
	* @param Q_INQ Element already in the queue
	* @param Q_TOINSERT Element to insert into queue
	* @param LINK_NAME Name of link field used to organize the queue
	**/
	#define Q_INSERT_BEFORE(Q_HEAD,Q_INQ,Q_TOINSERT,LINK_NAME) do { \
	Q_ASSERT_LINK(Q_TOINSERT, LINK_NAME); \
	Q_ASSERT_CONSISTENT(Q_HEAD, Q_INQ, LINK_NAME); \
	\
	(Q_TOINSERT)->LINK_NAME.next = (Q_INQ); \
	(Q_TOINSERT)->LINK_NAME.prev = (Q_INQ)->LINK_NAME.prev; \
	if ((Q_INQ)->LINK_NAME.prev) \
	(Q_INQ)->LINK_NAME.prev->LINK_NAME.next = Q_TOINSERT; \
	(Q_INQ)->LINK_NAME.prev = (Q_TOINSERT); \
	if ((Q_INQ) == (Q_HEAD)->head) \
	(Q_HEAD)->head = (Q_TOINSERT); \
	(Q_HEAD)->count++; \
	\
	Q_ASSERT_CONSISTENT(Q_HEAD, Q_TOINSERT, LINK_NAME); \
	} while (0)

	/**
	* @def Q_REMOVE(Q_HEAD,Q_ELEM,LINK_NAME)
	*
	* @brief Detaches the element Q_ELEM from the queue organized by LINK_NAME,
	* and returns a pointer to the element.
	*
	* If Q_HEAD does not use the link named LINK_NAME to organize its elements
	* the behavior of this macro is undefined.
	*
	* @param Q_HEAD Pointer to the head of the queue containing Q_ELEM. If
	* Q_REMOVE removes the first, last, or only element in the queue,
	* Q_HEAD should be updated appropriately.
	* @param Q_ELEM Pointer to the element to remove from the queue headed by
	* Q_HEAD.
	* @param LINK_NAME The name of the link used to organize Q_HEAD's queue
	*
	* @return Void
	**/
	#define Q_REMOVE(Q_HEAD,Q_ELEM,LINK_NAME) do { \
	Q_ASSERT_CONSISTENT(Q_HEAD, Q_ELEM, LINK_NAME); \
	if ((Q_ELEM)->LINK_NAME.prev) \
	(Q_ELEM)->LINK_NAME.prev->LINK_NAME.next=(Q_ELEM)->LINK_NAME.next; \
	if ((Q_ELEM)->LINK_NAME.next) \
	(Q_ELEM)->LINK_NAME.next->LINK_NAME.prev=(Q_ELEM)->LINK_NAME.prev; \
	if ((Q_ELEM) == (Q_HEAD)->head) \
	(Q_HEAD)->head = (Q_ELEM)->LINK_NAME.next; \
	if ((Q_ELEM) == (Q_HEAD)->tail) \
	(Q_HEAD)->tail = (Q_ELEM)->LINK_NAME.prev; \
	(Q_HEAD)->count--; \
	(Q_ELEM)->LINK_NAME.next = VQ_OFF_LIST; \
	(Q_ELEM)->LINK_NAME.prev = VQ_OFF_LIST; \
	} while (0)

	/**
	* @def Q_CONCAT(Q_HEAD1,Q_HEAD2,LINK_NAME)
	*
	* @brief Concatenates two lists together
	* @param Q_HEAD1 The first list
	* @param Q_HEAD2 The second list
	* @param LINK_NAME The name of the link used to organize Q_HEAD's queue
	*
	* @return Void
	**/
	#define Q_CONCAT(Q_HEAD1,Q_HEAD2,LINK_NAME) do { \
	if (!(Q_HEAD1)->head) { \
	(Q_HEAD1) = (Q_HEAD2); \
	} else if ((Q_HEAD2)->head) { \
	(Q_HEAD1)->tail->LINK_NAME.next = (Q_HEAD2)->head; \
	(Q_HEAD2)->head->LINK_NAME.prev = (Q_HEAD1)->tail; \
	(Q_HEAD1)->tail = (Q_HEAD2)->tail; \
	(Q_HEAD1)->count += (Q_HEAD2)->count; \
	} \
	(Q_HEAD2)->head = (Q_HEAD2)->tail = NULL; \
	(Q_HEAD2)->count = 0; \
	} while (0)


	/**
	* @def Q_FOREACH(CURRENT_ELEM,Q_HEAD,LINK_NAME)
	*
	* @brief Constructs an iterator block (like a for block) that operates
	* on each element in Q_HEAD, in order.
	*
	* Q_FOREACH constructs the head of a block of code that will iterate through
	* each element in the queue headed by Q_HEAD. Each time through the loop,
	* the variable named by CURRENT_ELEM will be set to point to a subsequent
	* element in the queue.
	*
	* Usage:<br>
	* Q_FOREACH(CURRENT_ELEM,Q_HEAD,LINK_NAME)<br>
	* {<br>
	* ... operate on the variable CURRENT_ELEM ... <br>
	* }
	*
	* If LINK_NAME is not used to organize the queue headed by Q_HEAD, then
	* the behavior of this macro is undefined.
	*
	* @param CURRENT_ELEM name of the variable to use for iteration. On each
	* loop through the Q_FOREACH block, CURRENT_ELEM will point to the
	* current element in the queue. CURRENT_ELEM should be an already-
	* defined variable name, and its type should be a pointer to
	* the type of data organized by Q_HEAD
	* @param Q_HEAD Pointer to the head of the queue to iterate through
	* @param LINK_NAME The name of the link used to organize the queue headed
	* by Q_HEAD.
	**/
	#define Q_FOREACH(CURRENT_ELEM,Q_HEAD,LINK_NAME) \
	for ((CURRENT_ELEM) = (Q_HEAD)->head; (CURRENT_ELEM); \
	(CURRENT_ELEM) = (CURRENT_ELEM)->LINK_NAME.next)

	/**
	* @def Q_SEARCH(OUTPUT,Q_HEAD,LINK_NAME,EXPR)
	*
	* @brief Searches each element in Q_HEAD for a node that satisfies
	* EXPR.
	*
	* @param OUTPUT name of the variable to use in the iteration. If a
	* node that satisfies EXPR is found, iteration is stopped and OUTPUT
	* is set as that value. If no node that satisfies EXPR is found,
	* OUTPUT will be NULL. In EXPR, OUTPUT will point the the current
	* node.
	* @param Q_HEAD Pointer to the head of the queue to iterate through
	* @param LINK_NAME The name of the link used to organize the queue headed
	* by Q_HEAD.
	* @param EXPR An expression that evaluates true when the wanted
	* element is seen
	**/
	#define Q_SEARCH(OUTPUT,Q_HEAD,LINK_NAME,EXPR) \
	do { \
	Q_FOREACH((OUTPUT),(Q_HEAD),LINK_NAME) { \
	if ((EXPR)) { \
	break; \
	} \
	} \
	} while (0)