text: /*
   * Copyright (C) the libgit2 contributors. All rights reserved.
   *
   * This file is part of libgit2, distributed under the GNU GPL v2 with
   * a Linking Exception. For full terms see the included COPYING file.
   *
   * This file is based on a modified version of the priority queue found
   * in the Apache project and libpqueue library.
   * 
   * https://github.com/vy/libpqueue
   * 
   * Original file notice:
   * 
   * Copyright 2010 Volkan Yazici <volkan.yazici@gmail.com>
   * Copyright 2006-2010 The Apache Software Foundation
   *
   * Licensed under the Apache License, Version 2.0 (the "License"); you may not
   * use this file except in compliance with the License. You may obtain a copy of
   * the License at
   *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
   * License for the specific language governing permissions and limitations under
   * the License.
   */
  
  #include "common.h"
  #include "pqueue.h"
  
  #define left(i)	((i) << 1)
  #define right(i) (((i) << 1) + 1)
  #define parent(i) ((i) >> 1)
  
  int git_pqueue_init(git_pqueue *q, size_t n, git_pqueue_cmp cmppri)
  {
  	assert(q);
  
  	/* Need to allocate n+1 elements since element 0 isn't used. */
  	q->d = git__malloc((n + 1) * sizeof(void *));
  	GITERR_CHECK_ALLOC(q->d);
  
  	q->size = 1;
  	q->avail = q->step = (n + 1); /* see comment above about n+1 */
  	q->cmppri = cmppri;
  
  	return 0;
  }
  
  
  void git_pqueue_free(git_pqueue *q)
  {
  	git__free(q->d);
  	q->d = NULL;
  }
  
  void git_pqueue_clear(git_pqueue *q)
  {
  	q->size = 1;
  }
  
  size_t git_pqueue_size(git_pqueue *q)
  {
  	/* queue element 0 exists but doesn't count since it isn't used. */
  	return (q->size - 1);
  }
  
  
  static void bubble_up(git_pqueue *q, size_t i)
  {
  	size_t parent_node;
  	void *moving_node = q->d[i];
  
  	for (parent_node = parent(i);
  			((i > 1) && q->cmppri(q->d[parent_node], moving_node));
  			i = parent_node, parent_node = parent(i)) {
  		q->d[i] = q->d[parent_node];
  	}
  
  	q->d[i] = moving_node;
  }
  
  
  static size_t maxchild(git_pqueue *q, size_t i)
  {
  	size_t child_node = left(i);
  
  	if (child_node >= q->size)
  		return 0;
  
  	if ((child_node + 1) < q->size &&
  		q->cmppri(q->d[child_node], q->d[child_node + 1]))
  		child_node++; /* use right child instead of left */
  
  	return child_node;
  }
  
  
  static void percolate_down(git_pqueue *q, size_t i)
  {
  	size_t child_node;
  	void *moving_node = q->d[i];
  
  	while ((child_node = maxchild(q, i)) != 0 &&
  			q->cmppri(moving_node, q->d[child_node])) {
  		q->d[i] = q->d[child_node];
  		i = child_node;
  	}
  
  	q->d[i] = moving_node;
  }
  
  
  int git_pqueue_insert(git_pqueue *q, void *d)
  {
  	void *tmp;
  	size_t i;
  	size_t newsize;
  
  	if (!q) return 1;
  
  	/* allocate more memory if necessary */
  	if (q->size >= q->avail) {
  		newsize = q->size + q->step;
  		tmp = git__realloc(q->d, sizeof(void *) * newsize);
  		GITERR_CHECK_ALLOC(tmp);
  
  		q->d = tmp;
  		q->avail = newsize;
  	}
  
  	/* insert item */
  	i = q->size++;
  	q->d[i] = d;
  	bubble_up(q, i);
  
  	return 0;
  }
  
  
  void *git_pqueue_pop(git_pqueue *q)
  {
  	void *head;
  
  	if (!q || q->size == 1)
  		return NULL;
  
  	head = q->d[1];
  	q->d[1] = q->d[--q->size];
  	percolate_down(q, 1);
  
  	return head;
  }
  
  
  void *git_pqueue_peek(git_pqueue *q)
  {
  	if (!q || q->size == 1)
  		return NULL;
  	return q->d[1];
  }
  