__NFDBITS
__size_t _n = __howmany(FD_SETSIZE, __NFDBITS); \
#define NFDBITS __NFDBITS
__fd_mask fds_bits[__howmany(FD_SETSIZE, __NFDBITS)];
p->fds_bits[fd / __NFDBITS] |= (1U << (fd % __NFDBITS));
p->fds_bits[fd / __NFDBITS] &= ~(1U << (fd % __NFDBITS));
return (p->fds_bits[fd / __NFDBITS] & (1U << (fd % __NFDBITS)));