Add HB_DIRECTION_IS_VALID
diff --git a/src/hb-common.h b/src/hb-common.h
index 26c056b..eefe984 100644
--- a/src/hb-common.h
+++ b/src/hb-common.h
@@ -118,6 +118,7 @@
#define HB_DIRECTION_IS_VERTICAL(dir) ((((unsigned int) (dir)) & ~1U) == 6)
#define HB_DIRECTION_IS_FORWARD(dir) ((((unsigned int) (dir)) & ~2U) == 4)
#define HB_DIRECTION_IS_BACKWARD(dir) ((((unsigned int) (dir)) & ~2U) == 5)
+#define HB_DIRECTION_IS_VALID(dir) ((((unsigned int) (dir)) & ~3U) == 4)
#define HB_DIRECTION_REVERSE(dir) ((hb_direction_t) (((unsigned int) (dir)) ^ 1))
