finished Time tests and fixed a corner case bug
diff --git a/aos/common/time.h b/aos/common/time.h
index 0440d91..9c86168 100644
--- a/aos/common/time.h
+++ b/aos/common/time.h
@@ -28,7 +28,8 @@
// not implemented because I can't think of any uses for them and there are
// multiple ways to do it. Division of Times by Times is implemented as the
// ratio of them. Multiplication, division, and modulus of Times by integers are
-// implemented as interpreting the argument as nanoseconds.
+// implemented as interpreting the argument as nanoseconds. Modulus takes the
+// sign from the first operand.
struct Time {
#ifdef SWIG
// All of the uses of constexpr here can safely be simply removed.