Replace pqueue with code from hashsig heap

I accidentally wrote a separate priority queue implementation when
I was working on file rename detection as part of the file hash
signature calculation code.  To simplify licensing terms, I just
adapted that to a general purpose priority queue and replace the
old priority queue implementation that was borrowed from elsewhere.

This also removes parts of the COPYING document that no longer
apply to libgit2.

1 files changed, 59 insertions, 125 deletions

diff --git a/src/pqueue.c b/src/pqueue.c
index 7819ed41e..ddbad7a54 100644
--- a/src/pqueue.c
+++ b/src/pqueue.c
@@ -3,161 +3,95 @@
  *
  * 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"
+#include "util.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;
-}
-
+#define PQUEUE_LCHILD_OF(I) (((I)<<1)+1)
+#define PQUEUE_RCHILD_OF(I) (((I)<<1)+2)
+#define PQUEUE_PARENT_OF(I) (((I)-1)>>1)
 
-void git_pqueue_free(git_pqueue *q)
+int git_pqueue_init(
+	git_pqueue *pq,
+	uint32_t flags,
+	size_t est_size,
+	git_vector_cmp cmp)
 {
-	git__free(q->d);
-	q->d = NULL;
+	pq->flags = flags;
+	pq->initial_size = est_size;
+	return git_vector_init(&pq->values, est_size, cmp);
 }
 
-void git_pqueue_clear(git_pqueue *q)
+void git_pqueue_free(git_pqueue *pq)
 {
-	q->size = 1;
+	git_vector_free(&pq->values);
 }
 
-size_t git_pqueue_size(git_pqueue *q)
+static void pqueue_up(git_pqueue *pq, size_t el)
 {
-	/* queue element 0 exists but doesn't count since it isn't used. */
-	return (q->size - 1);
-}
+	size_t parent_el = PQUEUE_PARENT_OF(el);
 
+	while (el > 0 && git_vector_cmp_elements(&pq->values, parent_el, el) > 0) {
+		git_vector_swap_elements(&pq->values, el, parent_el);
 
-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];
+		el = parent_el;
+		parent_el = PQUEUE_PARENT_OF(el);
 	}
-
-	q->d[i] = moving_node;
 }
 
-
-static size_t maxchild(git_pqueue *q, size_t i)
+static void pqueue_down(git_pqueue *pq, size_t el)
 {
-	size_t child_node = left(i);
+	size_t last = git_vector_length(&pq->values);
 
-	if (child_node >= q->size)
-		return 0;
+	while (1) {
+		size_t kid = PQUEUE_LCHILD_OF(el), rkid = PQUEUE_RCHILD_OF(el);
+		if (kid >= last)
+			break;
+		if (rkid < last && git_vector_cmp_elements(&pq->values, kid, rkid) > 0)
+			kid = rkid;
 
-	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;
-}
+		if (git_vector_cmp_elements(&pq->values, el, kid) < 0)
+			break;
 
-
-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;
+		git_vector_swap_elements(&pq->values, el, kid);
+		el = kid;
 	}
-
-	q->d[i] = moving_node;
 }
 
-
-int git_pqueue_insert(git_pqueue *q, void *d)
+int git_pqueue_insert(git_pqueue *pq, void *item)
 {
-	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;
+	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->values.length >= pq->initial_size)
+	{
+		/* skip item if below min item in heap */
+		if (pq->values._cmp(item, git_vector_get(&pq->values, 0)) <= 0)
+			return 0;
+		(void)git_pqueue_pop(pq);
 	}
 
-	/* insert item */
-	i = q->size++;
-	q->d[i] = d;
-	bubble_up(q, i);
+	error = git_vector_insert(&pq->values, item);
 
-	return 0;
-}
+	if (!error)
+		pqueue_up(pq, pq->values.length - 1);
 
-
-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;
+	return error;
 }
 
-
-void *git_pqueue_peek(git_pqueue *q)
+void *git_pqueue_pop(git_pqueue *pq)
 {
-	if (!q || q->size == 1)
-		return NULL;
-	return q->d[1];
+	void *rval = git_vector_get(&pq->values, 0);
+
+	if (git_vector_length(&pq->values) > 1) {
+		pq->values.contents[0] = git_vector_last(&pq->values);
+		git_vector_pop(&pq->values);
+		pqueue_down(pq, 0);
+	} else {
+		git_vector_pop(&pq->values);
+	}
+
+	return rval;
 }