Copy git_merge__bases_many() for new ahead-behind code

To be used as a basis for a function which marks nodes with parents
up to the merge base.

src/graph.c

@@ -10,6 +10,102 @@
 #include "merge.h"
 #include "git2/graph.h"
 
+static int interesting(git_pqueue *list)
+{
+	unsigned int i;
+	/* element 0 isn't used - we need to start at 1 */
+	for (i = 1; i < list->size; i++) {
+		git_commit_list_node *commit = list->d[i];
+		if ((commit->flags & STALE) == 0)
+			return 1;
+	}
+
+	return 0;
+}
+
+int git_merge__bases_many(git_commit_list **out, git_revwalk *walk, git_commit_list_node *one, git_vector *twos)
+{
+	int error;
+	unsigned int i;
+	git_commit_list_node *two;
+	git_commit_list *result = NULL, *tmp = NULL;
+	git_pqueue list;
+
+	/* if the commit is repeated, we have a our merge base already */
+	git_vector_foreach(twos, i, two) {
+		if (one == two)
+			return git_commit_list_insert(one, out) ? 0 : -1;
+	}
+
+	if (git_pqueue_init(&list, twos->length * 2, git_commit_list_time_cmp) < 0)
+		return -1;
+
+	if (git_commit_list_parse(walk, one) < 0)
+	    return -1;
+
+	one->flags |= PARENT1;
+	if (git_pqueue_insert(&list, one) < 0)
+		return -1;
+
+	git_vector_foreach(twos, i, two) {
+		git_commit_list_parse(walk, two);
+		two->flags |= PARENT2;
+		if (git_pqueue_insert(&list, two) < 0)
+			return -1;
+	}
+
+	/* as long as there are non-STALE commits */
+	while (interesting(&list)) {
+		git_commit_list_node *commit;
+		int flags;
+
+		commit = git_pqueue_pop(&list);
+
+		flags = commit->flags & (PARENT1 | PARENT2 | STALE);
+		if (flags == (PARENT1 | PARENT2)) {
+			if (!(commit->flags & RESULT)) {
+				commit->flags |= RESULT;
+				if (git_commit_list_insert(commit, &result) == NULL)
+					return -1;
+			}
+			/* we mark the parents of a merge stale */
+			flags |= STALE;
+		}
+
+		for (i = 0; i < commit->out_degree; i++) {
+			git_commit_list_node *p = commit->parents[i];
+			if ((p->flags & flags) == flags)
+				continue;
+
+			if ((error = git_commit_list_parse(walk, p)) < 0)
+				return error;
+
+			p->flags |= flags;
+			if (git_pqueue_insert(&list, p) < 0)
+				return -1;
+		}
+	}
+
+	git_pqueue_free(&list);
+
+	/* filter out any stale commits in the results */
+	tmp = result;
+	result = NULL;
+
+	while (tmp) {
+		struct git_commit_list *next = tmp->next;
+		if (!(tmp->item->flags & STALE))
+			if (git_commit_list_insert_by_date(tmp->item, &result) == NULL)
+				return -1;
+
+		git__free(tmp);
+		tmp = next;
+	}
+
+	*out = result;
+	return 0;
+}
+
 static int ahead_behind(git_commit_list_node *one, git_commit_list_node *two,
 	size_t *ahead, size_t *behind)
 {