heap.c revision 290001 
1/*
2 * Copyright (C) 2004-2007, 2010-2012  Internet Systems Consortium, Inc. ("ISC")
3 * Copyright (C) 1997-2001  Internet Software Consortium.
4 *
5 * Permission to use, copy, modify, and/or distribute this software for any
6 * purpose with or without fee is hereby granted, provided that the above
7 * copyright notice and this permission notice appear in all copies.
8 *
9 * THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
10 * REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
11 * AND FITNESS.  IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
12 * INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
13 * LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
14 * OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
15 * PERFORMANCE OF THIS SOFTWARE.
16 */
17
18/* $Id$ */
19
20/*! \file
21 * Heap implementation of priority queues adapted from the following:
22 *
23 *	\li "Introduction to Algorithms," Cormen, Leiserson, and Rivest,
24 *	MIT Press / McGraw Hill, 1990, ISBN 0-262-03141-8, chapter 7.
25 *
26 *	\li "Algorithms," Second Edition, Sedgewick, Addison-Wesley, 1988,
27 *	ISBN 0-201-06673-4, chapter 11.
28 */
29
30#include <config.h>
31
32#include <isc/heap.h>
33#include <isc/magic.h>
34#include <isc/mem.h>
35#include <isc/string.h>		/* Required for memcpy. */
36#include <isc/util.h>
37
38/*@{*/
39/*%
40 * Note: to make heap_parent and heap_left easy to compute, the first
41 * element of the heap array is not used; i.e. heap subscripts are 1-based,
42 * not 0-based.  The parent is index/2, and the left-child is index*2.
43 * The right child is index*2+1.
44 */
45#define heap_parent(i)			((i) >> 1)
46#define heap_left(i)			((i) << 1)
47/*@}*/
48
49#define SIZE_INCREMENT			1024
50
51#define HEAP_MAGIC			ISC_MAGIC('H', 'E', 'A', 'P')
52#define VALID_HEAP(h)			ISC_MAGIC_VALID(h, HEAP_MAGIC)
53
54/*%
55 * When the heap is in a consistent state, the following invariant
56 * holds true: for every element i > 1, heap_parent(i) has a priority
57 * higher than or equal to that of i.
58 */
59#define HEAPCONDITION(i) ((i) == 1 || \
60			  ! heap->compare(heap->array[(i)], \
61					  heap->array[heap_parent(i)]))
62
63/*% ISC heap structure. */
64struct isc_heap {
65	unsigned int			magic;
66	isc_mem_t *			mctx;
67	unsigned int			size;
68	unsigned int			size_increment;
69	unsigned int			last;
70	void				**array;
71	isc_heapcompare_t		compare;
72	isc_heapindex_t			index;
73};
74
75isc_result_t
76isc_heap_create(isc_mem_t *mctx, isc_heapcompare_t compare,
77		isc_heapindex_t index, unsigned int size_increment,
78		isc_heap_t **heapp)
79{
80	isc_heap_t *heap;
81
82	REQUIRE(heapp != NULL && *heapp == NULL);
83	REQUIRE(compare != NULL);
84
85	heap = isc_mem_get(mctx, sizeof(*heap));
86	if (heap == NULL)
87		return (ISC_R_NOMEMORY);
88	heap->magic = HEAP_MAGIC;
89	heap->size = 0;
90	heap->mctx = NULL;
91	isc_mem_attach(mctx, &heap->mctx);
92	if (size_increment == 0)
93		heap->size_increment = SIZE_INCREMENT;
94	else
95		heap->size_increment = size_increment;
96	heap->last = 0;
97	heap->array = NULL;
98	heap->compare = compare;
99	heap->index = index;
100
101	*heapp = heap;
102
103	return (ISC_R_SUCCESS);
104}
105
106void
107isc_heap_destroy(isc_heap_t **heapp) {
108	isc_heap_t *heap;
109
110	REQUIRE(heapp != NULL);
111	heap = *heapp;
112	REQUIRE(VALID_HEAP(heap));
113
114	if (heap->array != NULL)
115		isc_mem_put(heap->mctx, heap->array,
116			    heap->size * sizeof(void *));
117	heap->magic = 0;
118	isc_mem_putanddetach(&heap->mctx, heap, sizeof(*heap));
119
120	*heapp = NULL;
121}
122
123static isc_boolean_t
124resize(isc_heap_t *heap) {
125	void **new_array;
126	size_t new_size;
127
128	REQUIRE(VALID_HEAP(heap));
129
130	new_size = heap->size + heap->size_increment;
131	new_array = isc_mem_get(heap->mctx, new_size * sizeof(void *));
132	if (new_array == NULL)
133		return (ISC_FALSE);
134	if (heap->array != NULL) {
135		memcpy(new_array, heap->array, heap->size * sizeof(void *));
136		isc_mem_put(heap->mctx, heap->array,
137			    heap->size * sizeof(void *));
138	}
139	heap->size = new_size;
140	heap->array = new_array;
141
142	return (ISC_TRUE);
143}
144
145static void
146float_up(isc_heap_t *heap, unsigned int i, void *elt) {
147	unsigned int p;
148
149	for (p = heap_parent(i) ;
150	     i > 1 && heap->compare(elt, heap->array[p]) ;
151	     i = p, p = heap_parent(i)) {
152		heap->array[i] = heap->array[p];
153		if (heap->index != NULL)
154			(heap->index)(heap->array[i], i);
155	}
156	heap->array[i] = elt;
157	if (heap->index != NULL)
158		(heap->index)(heap->array[i], i);
159
160	INSIST(HEAPCONDITION(i));
161}
162
163static void
164sink_down(isc_heap_t *heap, unsigned int i, void *elt) {
165	unsigned int j, size, half_size;
166	size = heap->last;
167	half_size = size / 2;
168	while (i <= half_size) {
169		/* Find the smallest of the (at most) two children. */
170		j = heap_left(i);
171		if (j < size && heap->compare(heap->array[j+1],
172					      heap->array[j]))
173			j++;
174		if (heap->compare(elt, heap->array[j]))
175			break;
176		heap->array[i] = heap->array[j];
177		if (heap->index != NULL)
178			(heap->index)(heap->array[i], i);
179		i = j;
180	}
181	heap->array[i] = elt;
182	if (heap->index != NULL)
183		(heap->index)(heap->array[i], i);
184
185	INSIST(HEAPCONDITION(i));
186}
187
188isc_result_t
189isc_heap_insert(isc_heap_t *heap, void *elt) {
190	unsigned int new_last;
191
192	REQUIRE(VALID_HEAP(heap));
193
194	new_last = heap->last + 1;
195	RUNTIME_CHECK(new_last > 0); /* overflow check */
196	if (new_last >= heap->size && !resize(heap))
197		return (ISC_R_NOMEMORY);
198	heap->last = new_last;
199
200	float_up(heap, new_last, elt);
201
202	return (ISC_R_SUCCESS);
203}
204
205void
206isc_heap_delete(isc_heap_t *heap, unsigned int index) {
207	void *elt;
208	isc_boolean_t less;
209
210	REQUIRE(VALID_HEAP(heap));
211	REQUIRE(index >= 1 && index <= heap->last);
212
213	if (index == heap->last) {
214		heap->array[heap->last] = NULL;
215		heap->last--;
216	} else {
217		elt = heap->array[heap->last];
218		heap->array[heap->last] = NULL;
219		heap->last--;
220
221		less = heap->compare(elt, heap->array[index]);
222		heap->array[index] = elt;
223		if (less)
224			float_up(heap, index, heap->array[index]);
225		else
226			sink_down(heap, index, heap->array[index]);
227	}
228}
229
230void
231isc_heap_increased(isc_heap_t *heap, unsigned int index) {
232	REQUIRE(VALID_HEAP(heap));
233	REQUIRE(index >= 1 && index <= heap->last);
234
235	float_up(heap, index, heap->array[index]);
236}
237
238void
239isc_heap_decreased(isc_heap_t *heap, unsigned int index) {
240	REQUIRE(VALID_HEAP(heap));
241	REQUIRE(index >= 1 && index <= heap->last);
242
243	sink_down(heap, index, heap->array[index]);
244}
245
246void *
247isc_heap_element(isc_heap_t *heap, unsigned int index) {
248	REQUIRE(VALID_HEAP(heap));
249	REQUIRE(index >= 1);
250
251	if (index <= heap->last)
252		return (heap->array[index]);
253	return (NULL);
254}
255
256void
257isc_heap_foreach(isc_heap_t *heap, isc_heapaction_t action, void *uap) {
258	unsigned int i;
259
260	REQUIRE(VALID_HEAP(heap));
261	REQUIRE(action != NULL);
262
263	for (i = 1 ; i <= heap->last ; i++)
264		(action)(heap->array[i], uap);
265}
266