lib/isc/heap.c

	heap.c revision 4c713bf9401c2e55660bdcbba8d71032f482a330
/*
 * Copyright (C) 1997-2001, 2004-2007, 2010-2017  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/.
 */

/* $Id$ */

/*! \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 <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 isc_boolean_t
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 (ISC_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 (ISC_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;
    isc_boolean_t less;

    REQUIRE(VALID_HEAP(heap));
    REQUIRE(idx >= 1 && idx <= heap->last);

    heap_check(heap);
    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);
}