Avoid implementation-dependent promotion
Avoid implementation-dependent promotion

Some platforms failed to compile 9ad90309 with pedantry enabled, because
promotion rules caused sign-conversion in some cases.

Looking at the existing expression, it unnecessarily risks overflow.
Rewriting it (in a somewhat unnatural manner) to remove the risk of
overflow also clarifies a reasonable way to introduce a cast.

kulp/tenyr,kulp/tenyr,kulp/tenyr