contrib/bind-9.2.4rc7/lib/isc/heap.c

   1 /*
   2  * Copyright (C) 2004  Internet Systems Consortium, Inc. ("ISC")
   3  * Copyright (C) 1997-2001  Internet Software Consortium.
   4  *
   5  * Permission to use, copy, modify, and 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: heap.c,v 1.28.2.1 2004/03/09 06:11:46 marka Exp $ */
  19
  20 /*
  21  * Heap implementation of priority queues adapted from the following:
  22  *
  23  *      _Introduction to Algorithms_, Cormen, Leiserson, and Rivest,
  24  *      MIT Press / McGraw Hill, 1990, ISBN 0-262-03141-8, chapter 7.
  25  *
  26  *      _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  * Note: to make heap_parent and heap_left easy to compute, the first
  40  * element of the heap array is not used; i.e. heap subscripts are 1-based,
  41  * not 0-based.
  42  */
  43 #define heap_parent(i)                  ((i) >> 1)
  44 #define heap_left(i)                    ((i) << 1)
  45
  46 #define SIZE_INCREMENT                  1024
  47
  48 #define HEAP_MAGIC                      ISC_MAGIC('H', 'E', 'A', 'P')
  49 #define VALID_HEAP(h)                   ISC_MAGIC_VALID(h, HEAP_MAGIC)
  50
  51 /*
  52  * When the heap is in a consistent state, the following invariant
  53  * holds true: for every element i > 1, heap_parent(i) has a priority
  54  * higher than or equal to that of i.
  55  */
  56 #define HEAPCONDITION(i) ((i) == 1 || \
  57                           ! heap->compare(heap->array[(i)], \
  58                                           heap->array[heap_parent(i)]))
  59
  60 struct isc_heap {
  61         unsigned int                    magic;
  62         isc_mem_t *                     mctx;
  63         unsigned int                    size;
  64         unsigned int                    size_increment;
  65         unsigned int                    last;
  66         void                            **array;
  67         isc_heapcompare_t               compare;
  68         isc_heapindex_t                 index;
  69 };
  70
  71 isc_result_t
  72 isc_heap_create(isc_mem_t *mctx, isc_heapcompare_t compare,
  73                 isc_heapindex_t index, unsigned int size_increment,
  74                 isc_heap_t **heapp)
  75 {
  76         isc_heap_t *heap;
  77
  78         REQUIRE(heapp != NULL && *heapp == NULL);
  79         REQUIRE(compare != NULL);
  80
  81         heap = isc_mem_get(mctx, sizeof *heap);
  82         if (heap == NULL)
  83                 return (ISC_R_NOMEMORY);
  84         heap->magic = HEAP_MAGIC;
  85         heap->mctx = mctx;
  86         heap->size = 0;
  87         if (size_increment == 0)
  88                 heap->size_increment = SIZE_INCREMENT;
  89         else
  90                 heap->size_increment = size_increment;
  91         heap->last = 0;
  92         heap->array = NULL;
  93         heap->compare = compare;
  94         heap->index = index;
  95
  96         *heapp = heap;
  97
  98         return (ISC_R_SUCCESS);
  99 }
 100
 101 void
 102 isc_heap_destroy(isc_heap_t **heapp) {
 103         isc_heap_t *heap;
 104
 105         REQUIRE(heapp != NULL);
 106         heap = *heapp;
 107         REQUIRE(VALID_HEAP(heap));
 108
 109         if (heap->array != NULL)
 110                 isc_mem_put(heap->mctx, heap->array,
 111                             heap->size * sizeof (void *));
 112         heap->magic = 0;
 113         isc_mem_put(heap->mctx, heap, sizeof *heap);
 114
 115         *heapp = NULL;
 116 }
 117
 118 static isc_boolean_t
 119 resize(isc_heap_t *heap) {
 120         void **new_array;
 121         size_t new_size;
 122
 123         REQUIRE(VALID_HEAP(heap));
 124
 125         new_size = heap->size + heap->size_increment;
 126         new_array = isc_mem_get(heap->mctx, new_size * sizeof (void *));
 127         if (new_array == NULL)
 128                 return (ISC_FALSE);
 129         if (heap->array != NULL) {
 130                 memcpy(new_array, heap->array, heap->size * sizeof (void *));
 131                 isc_mem_put(heap->mctx, heap->array,
 132                             heap->size * sizeof (void *));
 133         }
 134         heap->size = new_size;
 135         heap->array = new_array;
 136
 137         return (ISC_TRUE);
 138 }
 139
 140 static void
 141 float_up(isc_heap_t *heap, unsigned int i, void *elt) {
 142         unsigned int p;
 143
 144         for (p = heap_parent(i);
 145              i > 1 && heap->compare(elt, heap->array[p]);
 146              i = p, p = heap_parent(i)) {
 147                 heap->array[i] = heap->array[p];
 148                 if (heap->index != NULL)
 149                         (heap->index)(heap->array[i], i);
 150         }
 151         heap->array[i] = elt;
 152         if (heap->index != NULL)
 153                 (heap->index)(heap->array[i], i);
 154
 155         INSIST(HEAPCONDITION(i));
 156 }
 157
 158 static void
 159 sink_down(isc_heap_t *heap, unsigned int i, void *elt) {
 160         unsigned int j, size, half_size;
 161         size = heap->last;
 162         half_size = size / 2;
 163         while (i <= half_size) {
 164                 /* Find the smallest of the (at most) two children. */
 165                 j = heap_left(i);
 166                 if (j < size && heap->compare(heap->array[j+1],
 167                                               heap->array[j]))
 168                         j++;
 169                 if (heap->compare(elt, heap->array[j]))
 170                         break;
 171                 heap->array[i] = heap->array[j];
 172                 if (heap->index != NULL)
 173                         (heap->index)(heap->array[i], i);
 174                 i = j;
 175         }
 176         heap->array[i] = elt;
 177         if (heap->index != NULL)
 178                 (heap->index)(heap->array[i], i);
 179
 180         INSIST(HEAPCONDITION(i));
 181 }
 182
 183 isc_result_t
 184 isc_heap_insert(isc_heap_t *heap, void *elt) {
 185         unsigned int i;
 186
 187         REQUIRE(VALID_HEAP(heap));
 188
 189         i = ++heap->last;
 190         if (heap->last >= heap->size && !resize(heap))
 191                 return (ISC_R_NOMEMORY);
 192
 193         float_up(heap, i, elt);
 194
 195         return (ISC_R_SUCCESS);
 196 }
 197
 198 void
 199 isc_heap_delete(isc_heap_t *heap, unsigned int i) {
 200         void *elt;
 201         isc_boolean_t less;
 202
 203         REQUIRE(VALID_HEAP(heap));
 204         REQUIRE(i >= 1 && i <= heap->last);
 205
 206         if (i == heap->last) {
 207                 heap->last--;
 208         } else {
 209                 elt = heap->array[heap->last--];
 210                 less = heap->compare(elt, heap->array[i]);
 211                 heap->array[i] = elt;
 212                 if (less)
 213                         float_up(heap, i, heap->array[i]);
 214                 else
 215                         sink_down(heap, i, heap->array[i]);
 216         }
 217 }
 218
 219 void
 220 isc_heap_increased(isc_heap_t *heap, unsigned int i) {
 221         REQUIRE(VALID_HEAP(heap));
 222         REQUIRE(i >= 1 && i <= heap->last);
 223
 224         float_up(heap, i, heap->array[i]);
 225 }
 226
 227 void
 228 isc_heap_decreased(isc_heap_t *heap, unsigned int i) {
 229         REQUIRE(VALID_HEAP(heap));
 230         REQUIRE(i >= 1 && i <= heap->last);
 231
 232         sink_down(heap, i, heap->array[i]);
 233 }
 234
 235 void *
 236 isc_heap_element(isc_heap_t *heap, unsigned int i) {
 237         REQUIRE(VALID_HEAP(heap));
 238         REQUIRE(i >= 1 && i <= heap->last);
 239
 240         return (heap->array[i]);
 241 }
 242
 243 void
 244 isc_heap_foreach(isc_heap_t *heap, isc_heapaction_t action, void *uap) {
 245         unsigned int i;
 246
 247         REQUIRE(VALID_HEAP(heap));
 248         REQUIRE(action != NULL);
 249
 250         for (i = 1; i <= heap->last; i++)
 251                 (action)(heap->array[i], uap);
 252 }