FD_SETBITMASK
unsigned long fds[(FD_SETSIZE + FD_SETBITMASK) / FD_SETIDXMASK];
~(1U << (__fd & FD_SETBITMASK)); \
1 << (__fd & FD_SETBITMASK); \
1U << (__fd & FD_SETBITMASK)); \
int __size = (FD_SETSIZE+FD_SETBITMASK) / FD_SETIDXMASK;\