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/*
* Copyright (C) Internet Systems Consortium, Inc. ("ISC")
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
* REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
* AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
* INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
* LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
* OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
* PERFORMANCE OF THIS SOFTWARE.
*/
/* $Id: heap.c,v 1.2 2020/02/12 13:05:04 jsg Exp $ */
/*! \file
* Heap implementation of priority queues adapted from the following:
*
* \li "Introduction to Algorithms," Cormen, Leiserson, and Rivest,
* MIT Press / McGraw Hill, 1990, ISBN 0-262-03141-8, chapter 7.
*
* \li "Algorithms," Second Edition, Sedgewick, Addison-Wesley, 1988,
* ISBN 0-201-06673-4, chapter 11.
*/
#include <stdlib.h>
#include <isc/heap.h>
#include <isc/magic.h>
#include <string.h>
#include <isc/util.h>
/*@{*/
/*%
* Note: to make heap_parent and heap_left easy to compute, the first
* element of the heap array is not used; i.e. heap subscripts are 1-based,
* not 0-based. The parent is index/2, and the left-child is index*2.
* The right child is index*2+1.
*/
#define heap_parent(i) ((i) >> 1)
#define heap_left(i) ((i) << 1)
/*@}*/
#define SIZE_INCREMENT 1024
#define HEAP_MAGIC ISC_MAGIC('H', 'E', 'A', 'P')
#define VALID_HEAP(h) ISC_MAGIC_VALID(h, HEAP_MAGIC)
/*%
* When the heap is in a consistent state, the following invariant
* holds true: for every element i > 1, heap_parent(i) has a priority
* higher than or equal to that of i.
*/
#define HEAPCONDITION(i) ((i) == 1 || \
! heap->compare(heap->array[(i)], \
heap->array[heap_parent(i)]))
/*% ISC heap structure. */
struct isc_heap {
unsigned int magic;
unsigned int size;
unsigned int size_increment;
unsigned int last;
void **array;
isc_heapcompare_t compare;
isc_heapindex_t index;
};
#ifdef ISC_HEAP_CHECK
static void
heap_check(isc_heap_t *heap) {
unsigned int i;
for (i = 1; i <= heap->last; i++) {
INSIST(HEAPCONDITION(i));
}
}
#else
#define heap_check(x) (void)0
#endif
isc_result_t
isc_heap_create(isc_heapcompare_t compare,
isc_heapindex_t idx, unsigned int size_increment,
isc_heap_t **heapp)
{
isc_heap_t *heap;
REQUIRE(heapp != NULL && *heapp == NULL);
REQUIRE(compare != NULL);
heap = malloc(sizeof(*heap));
if (heap == NULL)
return (ISC_R_NOMEMORY);
heap->magic = HEAP_MAGIC;
heap->size = 0;
if (size_increment == 0)
heap->size_increment = SIZE_INCREMENT;
else
heap->size_increment = size_increment;
heap->last = 0;
heap->array = NULL;
heap->compare = compare;
heap->index = idx;
*heapp = heap;
return (ISC_R_SUCCESS);
}
void
isc_heap_destroy(isc_heap_t **heapp) {
isc_heap_t *heap;
REQUIRE(heapp != NULL);
heap = *heapp;
REQUIRE(VALID_HEAP(heap));
free(heap->array);
heap->magic = 0;
free(heap);
*heapp = NULL;
}
static isc_boolean_t
resize(isc_heap_t *heap) {
void **new_array;
unsigned int new_size;
REQUIRE(VALID_HEAP(heap));
new_size = heap->size + heap->size_increment;
new_array = malloc(new_size * sizeof(void *));
if (new_array == NULL)
return (ISC_FALSE);
if (heap->array != NULL) {
memmove(new_array, heap->array, heap->size * sizeof(void *));
free(heap->array);
}
heap->size = new_size;
heap->array = new_array;
return (ISC_TRUE);
}
static void
float_up(isc_heap_t *heap, unsigned int i, void *elt) {
unsigned int p;
for (p = heap_parent(i) ;
i > 1 && heap->compare(elt, heap->array[p]) ;
i = p, p = heap_parent(i)) {
heap->array[i] = heap->array[p];
if (heap->index != NULL)
(heap->index)(heap->array[i], i);
}
heap->array[i] = elt;
if (heap->index != NULL)
(heap->index)(heap->array[i], i);
INSIST(HEAPCONDITION(i));
heap_check(heap);
}
static void
sink_down(isc_heap_t *heap, unsigned int i, void *elt) {
unsigned int j, size, half_size;
size = heap->last;
half_size = size / 2;
while (i <= half_size) {
/* Find the smallest of the (at most) two children. */
j = heap_left(i);
if (j < size && heap->compare(heap->array[j+1],
heap->array[j]))
j++;
if (heap->compare(elt, heap->array[j]))
break;
heap->array[i] = heap->array[j];
if (heap->index != NULL)
(heap->index)(heap->array[i], i);
i = j;
}
heap->array[i] = elt;
if (heap->index != NULL)
(heap->index)(heap->array[i], i);
INSIST(HEAPCONDITION(i));
heap_check(heap);
}
isc_result_t
isc_heap_insert(isc_heap_t *heap, void *elt) {
unsigned int new_last;
REQUIRE(VALID_HEAP(heap));
heap_check(heap);
new_last = heap->last + 1;
RUNTIME_CHECK(new_last > 0); /* overflow check */
if (new_last >= heap->size && !resize(heap))
return (ISC_R_NOMEMORY);
heap->last = new_last;
float_up(heap, new_last, elt);
return (ISC_R_SUCCESS);
}
void
isc_heap_delete(isc_heap_t *heap, unsigned int idx) {
void *elt;
isc_boolean_t less;
REQUIRE(VALID_HEAP(heap));
REQUIRE(idx >= 1 && idx <= heap->last);
heap_check(heap);
if (heap->index != NULL)
(heap->index)(heap->array[idx], 0);
if (idx == heap->last) {
heap->array[heap->last] = NULL;
heap->last--;
heap_check(heap);
} else {
elt = heap->array[heap->last];
heap->array[heap->last] = NULL;
heap->last--;
less = heap->compare(elt, heap->array[idx]);
heap->array[idx] = elt;
if (less)
float_up(heap, idx, heap->array[idx]);
else
sink_down(heap, idx, heap->array[idx]);
}
}
void
isc_heap_increased(isc_heap_t *heap, unsigned int idx) {
REQUIRE(VALID_HEAP(heap));
REQUIRE(idx >= 1 && idx <= heap->last);
float_up(heap, idx, heap->array[idx]);
}
void
isc_heap_decreased(isc_heap_t *heap, unsigned int idx) {
REQUIRE(VALID_HEAP(heap));
REQUIRE(idx >= 1 && idx <= heap->last);
sink_down(heap, idx, heap->array[idx]);
}
void *
isc_heap_element(isc_heap_t *heap, unsigned int idx) {
REQUIRE(VALID_HEAP(heap));
REQUIRE(idx >= 1);
heap_check(heap);
if (idx <= heap->last)
return (heap->array[idx]);
return (NULL);
}
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