1 /*
2 * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
3 *
4 * This Source Code Form is subject to the terms of the Mozilla Public
5 * License, v. 2.0. If a copy of the MPL was not distributed with this
6 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
7 *
8 * See the COPYRIGHT file distributed with this work for additional
9 * information regarding copyright ownership.
10 */
11
12 /*! \file
13 * Heap implementation of priority queues adapted from the following:
14 *
15 * \li "Introduction to Algorithms," Cormen, Leiserson, and Rivest,
16 * MIT Press / McGraw Hill, 1990, ISBN 0-262-03141-8, chapter 7.
17 *
18 * \li "Algorithms," Second Edition, Sedgewick, Addison-Wesley, 1988,
19 * ISBN 0-201-06673-4, chapter 11.
20 */
21
22 #include <stdbool.h>
23
24 #include <isc/heap.h>
25 #include <isc/magic.h>
26 #include <isc/mem.h>
27 #include <isc/string.h> /* Required for memmove. */
28 #include <isc/util.h>
29
30 /*@{*/
31 /*%
32 * Note: to make heap_parent and heap_left easy to compute, the first
33 * element of the heap array is not used; i.e. heap subscripts are 1-based,
34 * not 0-based. The parent is index/2, and the left-child is index*2.
35 * The right child is index*2+1.
36 */
37 #define heap_parent(i) ((i) >> 1)
38 #define heap_left(i) ((i) << 1)
39 /*@}*/
40
41 #define SIZE_INCREMENT 1024
42
43 #define HEAP_MAGIC ISC_MAGIC('H', 'E', 'A', 'P')
44 #define VALID_HEAP(h) ISC_MAGIC_VALID(h, HEAP_MAGIC)
45
46 /*%
47 * When the heap is in a consistent state, the following invariant
48 * holds true: for every element i > 1, heap_parent(i) has a priority
49 * higher than or equal to that of i.
50 */
51 #define HEAPCONDITION(i) \
52 ((i) == 1 || \
53 !heap->compare(heap->array[(i)], heap->array[heap_parent(i)]))
54
55 /*% ISC heap structure. */
56 struct isc_heap {
57 unsigned int magic;
58 isc_mem_t *mctx;
59 unsigned int size;
60 unsigned int size_increment;
61 unsigned int last;
62 void **array;
63 isc_heapcompare_t compare;
64 isc_heapindex_t index;
65 };
66
67 #ifdef ISC_HEAP_CHECK
68 static void
heap_check(isc_heap_t * heap)69 heap_check(isc_heap_t *heap) {
70 unsigned int i;
71 for (i = 1; i <= heap->last; i++) {
72 INSIST(HEAPCONDITION(i));
73 }
74 }
75 #else /* ifdef ISC_HEAP_CHECK */
76 #define heap_check(x) (void)0
77 #endif /* ifdef ISC_HEAP_CHECK */
78
79 isc_result_t
isc_heap_create(isc_mem_t * mctx,isc_heapcompare_t compare,isc_heapindex_t idx,unsigned int size_increment,isc_heap_t ** heapp)80 isc_heap_create(isc_mem_t *mctx, isc_heapcompare_t compare, isc_heapindex_t idx,
81 unsigned int size_increment, isc_heap_t **heapp) {
82 isc_heap_t *heap;
83
84 REQUIRE(heapp != NULL && *heapp == NULL);
85 REQUIRE(compare != NULL);
86
87 heap = isc_mem_get(mctx, sizeof(*heap));
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 }
97 heap->last = 0;
98 heap->array = NULL;
99 heap->compare = compare;
100 heap->index = idx;
101
102 *heapp = heap;
103
104 return (ISC_R_SUCCESS);
105 }
106
107 void
isc_heap_destroy(isc_heap_t ** heapp)108 isc_heap_destroy(isc_heap_t **heapp) {
109 isc_heap_t *heap;
110
111 REQUIRE(heapp != NULL);
112 heap = *heapp;
113 *heapp = NULL;
114 REQUIRE(VALID_HEAP(heap));
115
116 if (heap->array != NULL) {
117 isc_mem_put(heap->mctx, heap->array,
118 heap->size * sizeof(void *));
119 }
120 heap->magic = 0;
121 isc_mem_putanddetach(&heap->mctx, heap, sizeof(*heap));
122 }
123
124 static bool
resize(isc_heap_t * heap)125 resize(isc_heap_t *heap) {
126 void **new_array;
127 unsigned int new_size;
128
129 REQUIRE(VALID_HEAP(heap));
130
131 new_size = heap->size + heap->size_increment;
132 new_array = isc_mem_get(heap->mctx, new_size * sizeof(void *));
133 if (heap->array != NULL) {
134 memmove(new_array, heap->array, heap->size * sizeof(void *));
135 isc_mem_put(heap->mctx, heap->array,
136 heap->size * sizeof(void *));
137 }
138 heap->size = new_size;
139 heap->array = new_array;
140
141 return (true);
142 }
143
144 static void
float_up(isc_heap_t * heap,unsigned int i,void * elt)145 float_up(isc_heap_t *heap, unsigned int i, void *elt) {
146 unsigned int p;
147
148 for (p = heap_parent(i); i > 1 && heap->compare(elt, heap->array[p]);
149 i = p, p = heap_parent(i))
150 {
151 heap->array[i] = heap->array[p];
152 if (heap->index != NULL) {
153 (heap->index)(heap->array[i], i);
154 }
155 }
156 heap->array[i] = elt;
157 if (heap->index != NULL) {
158 (heap->index)(heap->array[i], i);
159 }
160
161 INSIST(HEAPCONDITION(i));
162 heap_check(heap);
163 }
164
165 static void
sink_down(isc_heap_t * heap,unsigned int i,void * elt)166 sink_down(isc_heap_t *heap, unsigned int i, void *elt) {
167 unsigned int j, size, half_size;
168 size = heap->last;
169 half_size = size / 2;
170 while (i <= half_size) {
171 /* Find the smallest of the (at most) two children. */
172 j = heap_left(i);
173 if (j < size &&
174 heap->compare(heap->array[j + 1], heap->array[j])) {
175 j++;
176 }
177 if (heap->compare(elt, heap->array[j])) {
178 break;
179 }
180 heap->array[i] = heap->array[j];
181 if (heap->index != NULL) {
182 (heap->index)(heap->array[i], i);
183 }
184 i = j;
185 }
186 heap->array[i] = elt;
187 if (heap->index != NULL) {
188 (heap->index)(heap->array[i], i);
189 }
190
191 INSIST(HEAPCONDITION(i));
192 heap_check(heap);
193 }
194
195 isc_result_t
isc_heap_insert(isc_heap_t * heap,void * elt)196 isc_heap_insert(isc_heap_t *heap, void *elt) {
197 unsigned int new_last;
198
199 REQUIRE(VALID_HEAP(heap));
200
201 heap_check(heap);
202 new_last = heap->last + 1;
203 RUNTIME_CHECK(new_last > 0); /* overflow check */
204 if (new_last >= heap->size && !resize(heap)) {
205 return (ISC_R_NOMEMORY);
206 }
207 heap->last = new_last;
208
209 float_up(heap, new_last, elt);
210
211 return (ISC_R_SUCCESS);
212 }
213
214 void
isc_heap_delete(isc_heap_t * heap,unsigned int idx)215 isc_heap_delete(isc_heap_t *heap, unsigned int idx) {
216 void *elt;
217 bool less;
218
219 REQUIRE(VALID_HEAP(heap));
220 REQUIRE(idx >= 1 && idx <= heap->last);
221
222 heap_check(heap);
223 if (heap->index != NULL) {
224 (heap->index)(heap->array[idx], 0);
225 }
226 if (idx == heap->last) {
227 heap->array[heap->last] = NULL;
228 heap->last--;
229 heap_check(heap);
230 } else {
231 elt = heap->array[heap->last];
232 heap->array[heap->last] = NULL;
233 heap->last--;
234
235 less = heap->compare(elt, heap->array[idx]);
236 heap->array[idx] = elt;
237 if (less) {
238 float_up(heap, idx, heap->array[idx]);
239 } else {
240 sink_down(heap, idx, heap->array[idx]);
241 }
242 }
243 }
244
245 void
isc_heap_increased(isc_heap_t * heap,unsigned int idx)246 isc_heap_increased(isc_heap_t *heap, unsigned int idx) {
247 REQUIRE(VALID_HEAP(heap));
248 REQUIRE(idx >= 1 && idx <= heap->last);
249
250 float_up(heap, idx, heap->array[idx]);
251 }
252
253 void
isc_heap_decreased(isc_heap_t * heap,unsigned int idx)254 isc_heap_decreased(isc_heap_t *heap, unsigned int idx) {
255 REQUIRE(VALID_HEAP(heap));
256 REQUIRE(idx >= 1 && idx <= heap->last);
257
258 sink_down(heap, idx, heap->array[idx]);
259 }
260
261 void *
isc_heap_element(isc_heap_t * heap,unsigned int idx)262 isc_heap_element(isc_heap_t *heap, unsigned int idx) {
263 REQUIRE(VALID_HEAP(heap));
264 REQUIRE(idx >= 1);
265
266 heap_check(heap);
267 if (idx <= heap->last) {
268 return (heap->array[idx]);
269 }
270 return (NULL);
271 }
272
273 void
isc_heap_foreach(isc_heap_t * heap,isc_heapaction_t action,void * uap)274 isc_heap_foreach(isc_heap_t *heap, isc_heapaction_t action, void *uap) {
275 unsigned int i;
276
277 REQUIRE(VALID_HEAP(heap));
278 REQUIRE(action != NULL);
279
280 for (i = 1; i <= heap->last; i++) {
281 (action)(heap->array[i], uap);
282 }
283 }
284