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/*
* Mach Operating System
* Copyright (c) 1991,1990,1989,1988,1987 Carnegie Mellon University
* All Rights Reserved.
*
* Permission to use, copy, modify and distribute this software and its
* documentation is hereby granted, provided that both the copyright
* notice and this permission notice appear in all copies of the
* software, derivative works or modified versions, and any portions
* thereof, and that both notices appear in supporting documentation.
*
* CARNEGIE MELLON ALLOWS FREE USE OF THIS SOFTWARE IN ITS "AS IS"
* CONDITION. CARNEGIE MELLON DISCLAIMS ANY LIABILITY OF ANY KIND FOR
* ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
*
* Carnegie Mellon requests users of this software to return to
*
* Software Distribution Coordinator or Software.Distribution@CS.CMU.EDU
* School of Computer Science
* Carnegie Mellon University
* Pittsburgh PA 15213-3890
*
* any improvements or extensions that they make and grant Carnegie Mellon
* the rights to redistribute these changes.
*/
/*
* Routines to implement queue package.
*/
#include "queue.h"
/*
* Insert element at head of queue.
*/
void enqueue_head(
register queue_t que,
register queue_entry_t elt)
{
elt->next = que->next;
elt->prev = que;
elt->next->prev = elt;
que->next = elt;
}
/*
* Insert element at tail of queue.
*/
void enqueue_tail(
register queue_t que,
register queue_entry_t elt)
{
elt->next = que;
elt->prev = que->prev;
elt->prev->next = elt;
que->prev = elt;
}
/*
* Remove and return element at head of queue.
*/
queue_entry_t dequeue_head(
register queue_t que)
{
register queue_entry_t elt;
if (que->next == que)
return((queue_entry_t)0);
elt = que->next;
elt->next->prev = que;
que->next = elt->next;
return(elt);
}
/*
* Remove and return element at tail of queue.
*/
queue_entry_t dequeue_tail(
register queue_t que)
{
register queue_entry_t elt;
if (que->prev == que)
return((queue_entry_t)0);
elt = que->prev;
elt->prev->next = que;
que->prev = elt->prev;
return(elt);
}
/*
* Remove arbitrary element from queue.
* Does not check whether element is on queue - the world
* will go haywire if it isn't.
*/
/*ARGSUSED*/
void remqueue(
queue_t que,
register queue_entry_t elt)
{
elt->next->prev = elt->prev;
elt->prev->next = elt->next;
}
/*
* Routines to directly imitate the VAX hardware queue
* package.
*/
void insque(
register struct queue_entry *entry,
register struct queue_entry *pred)
{
entry->next = pred->next;
entry->prev = pred;
(pred->next)->prev = entry;
pred->next = entry;
}
struct queue_entry
*remque(
register struct queue_entry *elt)
{
(elt->next)->prev = elt->prev;
(elt->prev)->next = elt->next;
return(elt);
}
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