Mountain Lion's implementation of libmath (located at /usr/lib/system/libsystem\_m.dylib) has all the standard libmath functions, plus, for each of them, a `$fenv_access_off` variation. For instance, there's `acos`, and `acos$fenv_access_off`. (I do not have any other version of Mac OS installed available to check if it was the case before 10.8.)

What does `$fenv_access_off` mean?

I understand that I won't ever be calling directly any of these, but I'm still curious about them.