1 files changed, 153 insertions, 0 deletions
diff --git a/src/pqueue.c b/src/pqueue.c
new file mode 100644
index 000000000..98152cb85
--- /dev/null
+++ b/src/pqueue.c
@@ -0,0 +1,153 @@
+/*
+ *	BORING COPYRIGHT NOTICE:
+ *
+ *	This file is a heavily modified version of the priority queue found
+ *	in the Apache project and the libpqueue library.
+ *
+ *		https://github.com/vy/libpqueue
+ *
+ *	These are the original authors:
+ *
+ *		Copyright 2010 Volkan Yazıcı <volkan.yazici@gmail.com>
+ *		Copyright 2006-2010 The Apache Software Foundation
+ *
+ *  This file is licensed under the Apache 2.0 license, which 
+ *  supposedly makes it compatible with the GPLv2 that libgit2 uses.
+ *
+ *  Check the Apache license at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  So much licensing trouble for a binary heap. Oh well.
+ */
+
+#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 = 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)
+{
+    free(q->d);
+	q->d = NULL;
+}
+
+
+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 = 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];
+}