lib/isc/heap.c

	heap.c revision 4c9406964425ecc33fac38bb093e236b43b449e6
/*
 * Copyright (C) 1997, 1998, 1999, 2000  Internet Software Consortium.
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND INTERNET SOFTWARE CONSORTIUM DISCLAIMS
 * ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL INTERNET SOFTWARE
 * CONSORTIUM BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
 * DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
 * PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
 * ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
 * SOFTWARE.
 */

/*
 * Heap implementation of priority queues adapted from the following:
 *
 *  _Introduction to Algorithms_, Cormen, Leiserson, and Rivest,
 *  MIT Press / McGraw Hill, 1990, ISBN 0-262-03141-8, chapter 7.
 *
 *  _Algorithms_, Second Edition, Sedgewick, Addison-Wesley, 1988,
 *  ISBN 0-201-06673-4, chapter 11.
 */

#include <config.h>

#include <isc/heap.h>
#include <isc/mem.h>
#include <isc/string.h>     /* Required for memcpy. */
#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.
 */
#define heap_parent(i)          ((i) >> 1)
#define heap_left(i)            ((i) << 1)

#define SIZE_INCREMENT          1024

#define HEAP_MAGIC          0x48454150U /* HEAP. */
#define VALID_HEAP(h)           ((h) != NULL && \
                     (h)->magic == 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 higher
 * priority than i.
 */
#define HEAPCONDITION(i) ((i) == 1 || \
              heap->compare(heap->array[heap_parent(i)], \
                    heap->array[(i)]))

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;
};

isc_result_t
isc_heap_create(isc_mem_t *mctx, isc_heapcompare_t compare,
        isc_heapindex_t index, 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->mctx = mctx;
    heap->size = 0;
    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 = index;

    *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_put(heap->mctx, heap, sizeof *heap);

    *heapp = NULL;
}

static isc_boolean_t
resize(isc_heap_t *heap) {
    void **new_array;
    size_t 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) {
        memcpy(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));
}

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));
}

isc_result_t
isc_heap_insert(isc_heap_t *heap, void *elt) {
    unsigned int i;

    REQUIRE(VALID_HEAP(heap));

    i = ++heap->last;
    if (heap->last >= heap->size && !resize(heap))
        return (ISC_R_NOMEMORY);

    float_up(heap, i, elt);

    return (ISC_R_SUCCESS);
}

void
isc_heap_delete(isc_heap_t *heap, unsigned int i) {
    void *elt;
    isc_boolean_t less;

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

    if (i == heap->last) {
        heap->last--;
    } else {
        elt = heap->array[heap->last--];
        less = heap->compare(elt, heap->array[i]);
        heap->array[i] = elt;
        if (less)
            float_up(heap, i, heap->array[i]);
        else
            sink_down(heap, i, heap->array[i]);
    }
}

void
isc_heap_increased(isc_heap_t *heap, unsigned int i) {
    REQUIRE(VALID_HEAP(heap));
    REQUIRE(i >= 1 && i <= heap->last);

    float_up(heap, i, heap->array[i]);
}

void
isc_heap_decreased(isc_heap_t *heap, unsigned int i) {
    REQUIRE(VALID_HEAP(heap));
    REQUIRE(i >= 1 && i <= heap->last);

    sink_down(heap, i, heap->array[i]);
}

void *
isc_heap_element(isc_heap_t *heap, unsigned int i) {
    REQUIRE(VALID_HEAP(heap));
    REQUIRE(i >= 1 && i <= heap->last);

    return (heap->array[i]);
}

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);
}