contrib/bind9/lib/isc/heap.c

   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. */
  64 struct 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
  75 isc_result_t
  76 isc_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
 106 void
 107 isc_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
 123 static isc_boolean_t
 124 resize(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
 145 static void
 146 float_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
 163 static void
 164 sink_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
 188 isc_result_t
 189 isc_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
 205 void
 206 isc_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
 230 void
 231 isc_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
 238 void
 239 isc_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
 246 void *
 247 isc_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
 256 void
 257 isc_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 }