[oakenshield]

The FAQ mainly complains about multi-statement macros that use conditionals or loops (among some sillier criticism). For a one-statement expression such as the above, I would use a macro because it's so much easier to define than a (potentially templatized) inline function.

Also, to answer your "how much is done for you by the compiler" question, gcc has a few builtins: __builtin_clz (count leading 0 bits), __builtin_popcount (number of 1 bits), etc. but it's not nearly enough for most common bit twiddling use-cases.

http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html