thodg/libgit2/src/pqueue.c

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• Hash : 0c7f49dd
  Author :
  Date : 2017-06-30T13:39:01
  

  Make sure to always include "common.h" first
  
  Next to including several files, our "common.h" header also declares
  various macros which are then used throughout the project. As such, we
  have to make sure to always include this file first in all
  implementation files. Otherwise, we might encounter problems or even
  silent behavioural differences due to macros or defines not being
  defined as they should be. So in fact, our header and implementation
  files should make sure to always include "common.h" first.
  
  This commit does so by establishing a common include pattern. Header
  files inside of "src" will now always include "common.h" as its first
  other file, separated by a newline from all the other includes to make
  it stand out as special. There are two cases for the implementation
  files. If they do have a matching header file, they will always include
  this one first, leading to "common.h" being transitively included as
  first file. If they do not have a matching header file, they instead
  include "common.h" as first file themselves.
  
  This fixes the outlined problems and will become our standard practice
  for header and source files inside of the "src/" from now on.
  

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• src/pqueue.c

• /*
   * 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.
   */
  
  #include "pqueue.h"
  
  #include "util.h"
  
  #define PQUEUE_LCHILD_OF(I) (((I)<<1)+1)
  #define PQUEUE_RCHILD_OF(I) (((I)<<1)+2)
  #define PQUEUE_PARENT_OF(I) (((I)-1)>>1)
  
  int git_pqueue_init(
  	git_pqueue *pq,
  	uint32_t flags,
  	size_t init_size,
  	git_vector_cmp cmp)
  {
  	int error = git_vector_init(pq, init_size, cmp);
  
  	if (!error) {
  		/* mix in our flags */
  		pq->flags |= flags;
  
  		/* if fixed size heap, pretend vector is exactly init_size elements */
  		if ((flags & GIT_PQUEUE_FIXED_SIZE) && init_size > 0)
  			pq->_alloc_size = init_size;
  	}
  
  	return error;
  }
  
  static void pqueue_up(git_pqueue *pq, size_t el)
  {
  	size_t parent_el = PQUEUE_PARENT_OF(el);
  	void *kid = git_vector_get(pq, el);
  
  	while (el > 0) {
  		void *parent = pq->contents[parent_el];
  
  		if (pq->_cmp(parent, kid) <= 0)
  			break;
  
  		pq->contents[el] = parent;
  
  		el = parent_el;
  		parent_el = PQUEUE_PARENT_OF(el);
  	}
  
  	pq->contents[el] = kid;
  }
  
  static void pqueue_down(git_pqueue *pq, size_t el)
  {
  	void *parent = git_vector_get(pq, el), *kid, *rkid;
  
  	while (1) {
  		size_t kid_el = PQUEUE_LCHILD_OF(el);
  
  		if ((kid = git_vector_get(pq, kid_el)) == NULL)
  			break;
  
  		if ((rkid = git_vector_get(pq, kid_el + 1)) != NULL &&
  			pq->_cmp(kid, rkid) > 0) {
  			kid    = rkid;
  			kid_el += 1;
  		}
  
  		if (pq->_cmp(parent, kid) <= 0)
  			break;
  
  		pq->contents[el] = kid;
  		el = kid_el;
  	}
  
  	pq->contents[el] = parent;
  }
  
  int git_pqueue_insert(git_pqueue *pq, void *item)
  {
  	int error = 0;
  
  	/* if heap is full, pop the top element if new one should replace it */
  	if ((pq->flags & GIT_PQUEUE_FIXED_SIZE) != 0 &&
  		pq->length >= pq->_alloc_size)
  	{
  		/* skip this item if below min item in heap or if
  		 * we do not have a comparison function */
  		if (!pq->_cmp || pq->_cmp(item, git_vector_get(pq, 0)) <= 0)
  			return 0;
  		/* otherwise remove the min item before inserting new */
  		(void)git_pqueue_pop(pq);
  	}
  
  	if (!(error = git_vector_insert(pq, item)) && pq->_cmp)
  		pqueue_up(pq, pq->length - 1);
  
  	return error;
  }
  
  void *git_pqueue_pop(git_pqueue *pq)
  {
  	void *rval;
  
  	if (!pq->_cmp) {
  		rval = git_vector_last(pq);
  	} else {
  		rval = git_pqueue_get(pq, 0);
  	}
  
  	if (git_pqueue_size(pq) > 1 && pq->_cmp) {
  		/* move last item to top of heap, shrink, and push item down */
  		pq->contents[0] = git_vector_last(pq);
  		git_vector_pop(pq);
  		pqueue_down(pq, 0);
  	} else {
  		/* all we need to do is shrink the heap in this case */
  		git_vector_pop(pq);
  	}
  
  	return rval;
  }
  

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