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/*

* Copyright (C) 2009-2012 the libgit2 contributors

*

* 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 "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. */

if ((q->d = git__malloc((n + 1) * sizeof(void *))) == NULL)

return GIT_ENOMEM;

q->size = 1;

q->avail = q->step = (n + 1); /* see comment above about n+1 */

q->cmppri = cmppri;

return GIT_SUCCESS;

}

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;

if ((tmp = git__realloc(q->d, sizeof(void *) * newsize)) == NULL)

return GIT_ENOMEM;

q->d = tmp;

q->avail = newsize;

}

/* insert item */

i = q->size++;

q->d[i] = d;

bubble_up(q, i);

return GIT_SUCCESS;

}

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];

}