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/* Copyright (C) 2000 MySQL AB
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
/*
Code for generell handling of priority Queues.
Implemention of queues from "Algoritms in C" by Robert Sedgewick.
*/
#include "mysys_priv.h"
#include "mysys_err.h"
#include <queues.h>
/* Init queue */
int init_queue(QUEUE *queue, uint max_elements, uint offset_to_key,
pbool max_at_top, int (*compare) (void *, byte *, byte *),
void *first_cmp_arg)
{
DBUG_ENTER("init_queue");
if ((queue->root= (byte **) my_malloc((max_elements+1)*sizeof(void*),
MYF(MY_WME))) == 0)
DBUG_RETURN(1);
queue->elements=0;
queue->compare=compare;
queue->first_cmp_arg=first_cmp_arg;
queue->max_elements=max_elements;
queue->offset_to_key=offset_to_key;
queue->max_at_top= max_at_top ? (-1 ^ 1) : 0;
DBUG_RETURN(0);
}
/*
Reinitialize queue for new usage; Note that you can't currently resize
the number of elements! If you need this, fix it :)
*/
int reinit_queue(QUEUE *queue, uint max_elements, uint offset_to_key,
pbool max_at_top, int (*compare) (void *, byte *, byte *),
void *first_cmp_arg)
{
DBUG_ENTER("reinit_queue");
if (queue->max_elements < max_elements)
/* It's real easy to do realloc here, just don't want to bother */
DBUG_RETURN(my_errno=EE_OUTOFMEMORY);
queue->elements=0;
queue->compare=compare;
queue->first_cmp_arg=first_cmp_arg;
queue->offset_to_key=offset_to_key;
queue->max_at_top= max_at_top ? (-1 ^ 1) : 0;
DBUG_RETURN(0);
}
void delete_queue(QUEUE *queue)
{
DBUG_ENTER("delete_queue");
if (queue->root)
{
my_free((gptr) queue->root,MYF(0));
queue->root=0;
}
DBUG_VOID_RETURN;
}
/* Code for insert, search and delete of elements */
void queue_insert(register QUEUE *queue, byte *element)
{
reg2 uint idx,next;
int cmp;
#ifndef DBUG_OFF
if (queue->elements < queue->max_elements)
#endif
{
queue->root[0]=element;
idx= ++queue->elements;
/* max_at_top swaps the comparison if we want to order by desc */
while ((cmp=queue->compare(queue->first_cmp_arg,
element+queue->offset_to_key,
queue->root[(next=idx >> 1)] +
queue->offset_to_key)) &&
(cmp ^ queue->max_at_top) < 0)
{
queue->root[idx]=queue->root[next];
idx=next;
}
queue->root[idx]=element;
}
}
/* Remove item from queue */
/* Returns pointer to removed element */
byte *queue_remove(register QUEUE *queue, uint idx)
{
#ifndef DBUG_OFF
if (idx >= queue->max_elements)
return 0;
#endif
{
byte *element=queue->root[++idx]; /* Intern index starts from 1 */
queue->root[idx]=queue->root[queue->elements--];
_downheap(queue,idx);
return element;
}
}
/* Fix when element on top has been replaced */
#ifndef queue_replaced
void queue_replaced(queue)
QUEUE *queue;
{
_downheap(queue,1);
}
#endif
/* Fix heap when index have changed */
void _downheap(register QUEUE *queue, uint idx)
{
byte *element;
uint elements,half_queue,next_index,offset_to_key;
int cmp;
offset_to_key=queue->offset_to_key;
element=queue->root[idx];
half_queue=(elements=queue->elements) >> 1;
while (idx <= half_queue)
{
next_index=idx+idx;
if (next_index < elements &&
(queue->compare(queue->first_cmp_arg,
queue->root[next_index]+offset_to_key,
queue->root[next_index+1]+offset_to_key) ^
queue->max_at_top) > 0)
next_index++;
if ((cmp=queue->compare(queue->first_cmp_arg,
queue->root[next_index]+offset_to_key,
element+offset_to_key)) == 0 ||
(cmp ^ queue->max_at_top) > 0)
break;
queue->root[idx]=queue->root[next_index];
idx=next_index;
}
queue->root[idx]=element;
}
static int queue_fix_cmp(QUEUE *queue, void **a, void **b)
{
return queue->compare(queue->first_cmp_arg,
(char*) (*a)+queue->offset_to_key,
(char*) (*b)+queue->offset_to_key);
}
/*
Fix heap when every element was changed
actually, it can be done in linear time,
not in n*log(n), but some code (myisam/ft_boolean_search.c)
requires a strict order here, not just a queue property
*/
void queue_fix(QUEUE *queue)
{
qsort2(queue->root+1,queue->elements, sizeof(void *),
(qsort2_cmp)queue_fix_cmp, queue);
}
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