NFDBITS            51 os/tpf/os.h            fd_mask fds_bits [howmany(FD_SETSIZE, NFDBITS)];
NFDBITS            54 os/tpf/os.h    #define FD_CLR(n, p)((p)->fds_bits[(n)/NFDBITS] &= ~(1 << ((n) % NFDBITS)))
NFDBITS            55 os/tpf/os.h    #define FD_ISSET(n, p)((p)->fds_bits[(n)/NFDBITS] & (1 <<((n) % NFDBITS)))