common/isc/heap.c

/*
 * Copyright (c) 2004 by Internet Systems Consortium, Inc. ("ISC")
 * Copyright (c) 1997,1999 by 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 ISC DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS.  IN NO EVENT SHALL ISC 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.
 */

#if !defined(LINT) && !defined(CODECENTER)
static const char rcsid[] = "$Id: heap.c,v 1.4 2006/03/09 23:57:56 marka Exp $";
#endif /* not lint */

#include "port_before.h"

#include <stddef.h>
#include <stdlib.h>
#include <errno.h>

#include "port_after.h"

#include <isc/heap.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 ARRAY_SIZE_INCREMENT 512

heap_context
heap_new(heap_higher_priority_func higher_priority, heap_index_func index,
     int array_size_increment) {
    heap_context ctx;

    if (higher_priority == NULL)
        return (NULL);

    ctx = (heap_context)malloc(sizeof (struct heap_context));
    if (ctx == NULL)
        return (NULL);

    ctx->array_size = 0;
    if (array_size_increment == 0)
        ctx->array_size_increment = ARRAY_SIZE_INCREMENT;
    else
        ctx->array_size_increment = array_size_increment;
    ctx->heap_size = 0;
    ctx->heap = NULL;
    ctx->higher_priority = higher_priority;
    ctx->index = index;
    return (ctx);
}

int
heap_free(heap_context ctx) {
    if (ctx == NULL) {
        errno = EINVAL;
        return (-1);
    }

    if (ctx->heap != NULL)
        free(ctx->heap);
    free(ctx);

    return (0);
}

static int
heap_resize(heap_context ctx) {
    void **new_heap;

    ctx->array_size += ctx->array_size_increment;
    new_heap = (void **)realloc(ctx->heap,
                    (ctx->array_size) * (sizeof (void *)));
    if (new_heap == NULL) {
        errno = ENOMEM;
        return (-1);
    }
    ctx->heap = new_heap;
    return (0);
}

static void
float_up(heap_context ctx, int i, void *elt) {
    int p;

    for ( p = heap_parent(i);
          i > 1 && ctx->higher_priority(elt, ctx->heap[p]);
          i = p, p = heap_parent(i) ) {
        ctx->heap[i] = ctx->heap[p];
        if (ctx->index != NULL)
            (ctx->index)(ctx->heap[i], i);
    }
    ctx->heap[i] = elt;
    if (ctx->index != NULL)
        (ctx->index)(ctx->heap[i], i);
}

static void
sink_down(heap_context ctx, int i, void *elt) {
    int j, size, half_size;

    size = ctx->heap_size;
    half_size = size / 2;
    while (i <= half_size) {
        /* find smallest of the (at most) two children */
        j = heap_left(i);
        if (j < size && ctx->higher_priority(ctx->heap[j+1],
                             ctx->heap[j]))
            j++;
        if (ctx->higher_priority(elt, ctx->heap[j]))
            break;
        ctx->heap[i] = ctx->heap[j];
        if (ctx->index != NULL)
            (ctx->index)(ctx->heap[i], i);
        i = j;
    }
    ctx->heap[i] = elt;
    if (ctx->index != NULL)
        (ctx->index)(ctx->heap[i], i);
}

int
heap_insert(heap_context ctx, void *elt) {
    int i;

    if (ctx == NULL || elt == NULL) {
        errno = EINVAL;
        return (-1);
    }

    i = ++ctx->heap_size;
    if (ctx->heap_size >= ctx->array_size && heap_resize(ctx) < 0)
        return (-1);

    float_up(ctx, i, elt);

    return (0);
}

int
heap_delete(heap_context ctx, int i) {
    void *elt;
    int less;

    if (ctx == NULL || i < 1 || i > ctx->heap_size) {
        errno = EINVAL;
        return (-1);
    }

    if (i == ctx->heap_size) {
        ctx->heap_size--;
    } else {
        elt = ctx->heap[ctx->heap_size--];
        less = ctx->higher_priority(elt, ctx->heap[i]);
        ctx->heap[i] = elt;
        if (less)
            float_up(ctx, i, ctx->heap[i]);
        else
            sink_down(ctx, i, ctx->heap[i]);
    }

    return (0);
}

int
heap_increased(heap_context ctx, int i) {
        if (ctx == NULL || i < 1 || i > ctx->heap_size) {
        errno = EINVAL;
        return (-1);
    }

    float_up(ctx, i, ctx->heap[i]);

    return (0);
}

int
heap_decreased(heap_context ctx, int i) {
        if (ctx == NULL || i < 1 || i > ctx->heap_size) {
        errno = EINVAL;
        return (-1);
    }

    sink_down(ctx, i, ctx->heap[i]);

    return (0);
}

void *
heap_element(heap_context ctx, int i) {
    if (ctx == NULL || i < 1 || i > ctx->heap_size) {
        errno = EINVAL;
        return (NULL);
    }

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

int
heap_for_each(heap_context ctx, heap_for_each_func action, void *uap) {
    int i;

    if (ctx == NULL || action == NULL) {
        errno = EINVAL;
        return (-1);
    }

    for (i = 1; i <= ctx->heap_size; i++)
        (action)(ctx->heap[i], uap);
    return (0);
}

/*! \file */