/*
 * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
 *
 * Permission to use, copy, modify, and/or 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.
 */

/* $Id: heap.c,v 1.7 2020/09/14 08:40:44 florian Exp $ */

/*! \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 <stdlib.h>
#include <isc/heap.h>
#include <string.h>
#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

/*%
 * 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                    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_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 = malloc(sizeof(*heap));
        if (heap == NULL)
                return (ISC_R_NOMEMORY);
        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 = idx;

        *heapp = heap;

        return (ISC_R_SUCCESS);
}

void
isc_heap_destroy(isc_heap_t **heapp) {
        isc_heap_t *heap;

        REQUIRE(heapp != NULL);
        heap = *heapp;

        free(heap->array);
        free(heap);

        *heapp = NULL;
}

static int
resize(isc_heap_t *heap) {
        void **new_array;
        unsigned int new_size;

        new_size = heap->size + heap->size_increment;
        new_array = reallocarray(NULL, new_size, sizeof(void *));
        if (new_array == NULL)
                return (0);
        if (heap->array != NULL) {
                memmove(new_array, heap->array, heap->size * sizeof(void *));
                free(heap->array);
        }
        heap->size = new_size;
        heap->array = new_array;

        return (1);
}

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 new_last;

        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;
        int less;

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

        if (heap->index != NULL)
                (heap->index)(heap->array[idx], 0);
        if (idx == heap->last) {
                heap->array[heap->last] = NULL;
                heap->last--;
        } 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(idx >= 1 && idx <= heap->last);

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

void
isc_heap_decreased(isc_heap_t *heap, unsigned int idx) {
        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(idx >= 1);

        if (idx <= heap->last)
                return (heap->array[idx]);
        return (NULL);
}