/*

 * Copyright (C) Internet Systems Consortium, Inc. ("ISC")

 *

 * SPDX-License-Identifier: MPL-2.0

 *

 * 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 https://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 <stdbool.h>

#include <isc/heap.h>

#include <isc/magic.h>

#include <isc/mem.h>

#include <isc/overflow.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 /* ifdef ISC_HEAP_CHECK */

#define heap_check(x) (void)0

#endif /* ifdef ISC_HEAP_CHECK */

void

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));

  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;

}

void

isc_heap_destroy(isc_heap_t **heapp) {

  isc_heap_t *heap;

  REQUIRE(heapp != NULL);

  heap = *heapp;

  *heapp = NULL;

  REQUIRE(VALID_HEAP(heap));

  if (heap->array != NULL) {

    isc_mem_cput(heap->mctx, heap->array, heap->size,

           sizeof(void *));

  }

  heap->magic = 0;

  isc_mem_putanddetach(&heap->mctx, heap, sizeof(*heap));

}

static void

resize(isc_heap_t *heap) {

  unsigned int new_size, new_bytes, old_bytes;

  REQUIRE(VALID_HEAP(heap));

  new_size = ISC_CHECKED_ADD(heap->size, heap->size_increment);

  new_bytes = ISC_CHECKED_MUL(new_size, sizeof(void *));

  old_bytes = ISC_CHECKED_MUL(heap->size, sizeof(void *));

  heap->size = new_size;

  heap->array = isc_mem_creget(heap->mctx, heap->array, old_bytes,

             new_bytes, sizeof(char));

}

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);

}

void

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);

  }

  heap->last = new_last;

  float_up(heap, new_last, elt);

}

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);

  }

}