Add comment.
diff --git a/src/smooth/ftgrays.c b/src/smooth/ftgrays.c
index 9b008a0..885b0df 100644
--- a/src/smooth/ftgrays.c
+++ b/src/smooth/ftgrays.c
@@ -1083,6 +1083,8 @@ typedef ptrdiff_t FT_PtrDist;
if ( dx < ONE_PIXEL / 4 )
goto Draw;
+ /* we can calculate the number of necessary bisections because */
+ /* each bisection predictably reduces deviation at least 4-fold */
level = 0;
do
{