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#define NBBY 8 /* number of bits in a byte */
/*
* Select uses bit masks of file descriptors in longs.
* These macros manipulate such bit fields (the filesystem macros use chars).
* FD_SETSIZE may be defined by the user, but the default here
* should be >= CHANNELCNT (SYSGEN parameter)
*/
#ifndef FD_SETSIZE
#define FD_SETSIZE 512
#endif
#define CHANNELSIZE 16 /* Size of a channel */
typedef long fd_mask;
#define NFDBITS (sizeof(fd_mask) * NBBY) /* bits per mask */
#ifndef howmany
#define howmany(x, y) (((x)+((y)-1))/(y))
#endif
typedef struct fd_set {
fd_mask fds_bits[howmany(FD_SETSIZE, NFDBITS)];
} fd_set;
#define FD_SET(n, p) ((p)->fds_bits[(n)/CHANNELSIZE/NFDBITS] |= (1 << (((n)/CHANNELSIZE) % NFDBITS)))
#define FD_CLR(n, p) ((p)->fds_bits[(n)/CHANNELSIZE/NFDBITS] &= ~(1 << (((n)/CHANNELSIZE) % NFDBITS)))
#define FD_ISSET(n, p) ((!((n) % CHANNELSIZE)) && ((p)->fds_bits[(n)/CHANNELSIZE/NFDBITS] & (1 << (((n)/CHANNELSIZE) % NFDBITS))))
#define FD_ZERO(p) memset((char *)(p),'\0',sizeof(*(p)))
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