NFDBITS
fd_mask bits[((FD_SETSIZE) + ((NFDBITS) - 1)) / (NFDBITS)];
#define _FD_BITSINDEX(fd) ((fd) / NFDBITS)
#define _FD_BIT(fd) (1L << ((fd) % NFDBITS))
tmp = howmany(maxfd+1, NFDBITS) * sizeof(fd_mask);
nfds = howmany(sock + 1, NFDBITS);
fdsn = howmany(sock + 1, NFDBITS) * sizeof(fd_mask);
uint32 bytes = HOWMANY(count, NFDBITS) * sizeof(fd_mask);
memset(set, 0, HOWMANY(numFDs, NFDBITS) * sizeof(fd_mask));
uint32 bytes = HOWMANY(numFDs, NFDBITS) * sizeof(fd_mask);