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+/*
+ * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ *
+ * See the COPYRIGHT file distributed with this work for additional
+ * information regarding copyright ownership.
+ */
+
+
+/*! \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 <config.h>
+
+#include <stdbool.h>
+
+#include <isc/heap.h>
+#include <isc/magic.h>
+#include <isc/mem.h>
+#include <isc/string.h> /* Required for memmove. */
+#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;
+ isc_mem_t * mctx;
+ 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_mem_t *mctx, 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 = isc_mem_get(mctx, sizeof(*heap));
+ if (heap == NULL)
+ return (ISC_R_NOMEMORY);
+ heap->magic = HEAP_MAGIC;
+ heap->size = 0;
+ heap->mctx = NULL;
+ isc_mem_attach(mctx, &heap->mctx);
+ 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));
+
+ if (heap->array != NULL)
+ isc_mem_put(heap->mctx, heap->array,
+ heap->size * sizeof(void *));
+ heap->magic = 0;
+ isc_mem_putanddetach(&heap->mctx, heap, sizeof(*heap));
+
+ *heapp = NULL;
+}
+
+static bool
+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 = isc_mem_get(heap->mctx, new_size * sizeof(void *));
+ if (new_array == NULL)
+ return (false);
+ if (heap->array != NULL) {
+ memmove(new_array, heap->array, heap->size * sizeof(void *));
+ isc_mem_put(heap->mctx, heap->array,
+ heap->size * sizeof(void *));
+ }
+ heap->size = new_size;
+ heap->array = new_array;
+
+ return (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;
+ bool 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);
+}
+
+void
+isc_heap_foreach(isc_heap_t *heap, isc_heapaction_t action, void *uap) {
+ unsigned int i;
+
+ REQUIRE(VALID_HEAP(heap));
+ REQUIRE(action != NULL);
+
+ for (i = 1 ; i <= heap->last ; i++)
+ (action)(heap->array[i], uap);
+}
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