Using the full width of the CPU's native word size shouldn't cost
anything in typical cases.  When working with large bitmapsets,
this halves the number of operations needed for many common BMS
operations.  On the right sort of test case, a measurable improvement
is obtained.

David Rowley

Discussion: https://postgr.es/m/CAKJS1f9EGBd2h-VkXvb=51tf+X46zMX5T8h-KYgXEV_u2zmLUw@mail.gmail.com