1 files changed, 113 insertions, 0 deletions
diff --git a/commit-reach.c b/commit-reach.c
index cd990dce16..c1edeb4610 100644
--- a/commit-reach.c
+++ b/commit-reach.c
@@ -1044,3 +1044,116 @@ void ahead_behind(struct repository *r,
 	clear_bit_arrays(&bit_arrays);
 	clear_prio_queue(&queue);
 }
+
+struct commit_and_index {
+	struct commit *commit;
+	unsigned int index;
+	timestamp_t generation;
+};
+
+static int compare_commit_and_index_by_generation(const void *va, const void *vb)
+{
+	const struct commit_and_index *a = (const struct commit_and_index *)va;
+	const struct commit_and_index *b = (const struct commit_and_index *)vb;
+
+	if (a->generation > b->generation)
+		return 1;
+	if (a->generation < b->generation)
+		return -1;
+	return 0;
+}
+
+void tips_reachable_from_bases(struct repository *r,
+			       struct commit_list *bases,
+			       struct commit **tips, size_t tips_nr,
+			       int mark)
+{
+	struct commit_and_index *commits;
+	size_t min_generation_index = 0;
+	timestamp_t min_generation;
+	struct commit_list *stack = NULL;
+
+	if (!bases || !tips || !tips_nr)
+		return;
+
+	/*
+	 * Do a depth-first search starting at 'bases' to search for the
+	 * tips. Stop at the lowest (un-found) generation number. When
+	 * finding the lowest commit, increase the minimum generation
+	 * number to the next lowest (un-found) generation number.
+	 */
+
+	CALLOC_ARRAY(commits, tips_nr);
+
+	for (size_t i = 0; i < tips_nr; i++) {
+		commits[i].commit = tips[i];
+		commits[i].index = i;
+		commits[i].generation = commit_graph_generation(tips[i]);
+	}
+
+	/* Sort with generation number ascending. */
+	QSORT(commits, tips_nr, compare_commit_and_index_by_generation);
+	min_generation = commits[0].generation;
+
+	while (bases) {
+		repo_parse_commit(r, bases->item);
+		commit_list_insert(bases->item, &stack);
+		bases = bases->next;
+	}
+
+	while (stack) {
+		int explored_all_parents = 1;
+		struct commit_list *p;
+		struct commit *c = stack->item;
+		timestamp_t c_gen = commit_graph_generation(c);
+
+		/* Does it match any of our tips? */
+		for (size_t j = min_generation_index; j < tips_nr; j++) {
+			if (c_gen < commits[j].generation)
+				break;
+
+			if (commits[j].commit == c) {
+				tips[commits[j].index]->object.flags |= mark;
+
+				if (j == min_generation_index) {
+					unsigned int k = j + 1;
+					while (k < tips_nr &&
+					       (tips[commits[k].index]->object.flags & mark))
+						k++;
+
+					/* Terminate early if all found. */
+					if (k >= tips_nr)
+						goto done;
+
+					min_generation_index = k;
+					min_generation = commits[k].generation;
+				}
+			}
+		}
+
+		for (p = c->parents; p; p = p->next) {
+			repo_parse_commit(r, p->item);
+
+			/* Have we already explored this parent? */
+			if (p->item->object.flags & SEEN)
+				continue;
+
+			/* Is it below the current minimum generation? */
+			if (commit_graph_generation(p->item) < min_generation)
+				continue;
+
+			/* Ok, we will explore from here on. */
+			p->item->object.flags |= SEEN;
+			explored_all_parents = 0;
+			commit_list_insert(p->item, &stack);
+			break;
+		}
+
+		if (explored_all_parents)
+			pop_commit(&stack);
+	}
+
+done:
+	free(commits);
+	repo_clear_commit_marks(r, SEEN);
+}