RQUEUEMASK
#define RQUEUESIZE (RQUEUEMASK + 1)
head = ch->ch_r_head & RQUEUEMASK;
tail = ch->ch_r_tail & RQUEUEMASK;
qleft += RQUEUEMASK + 1;
tail = (tail + 1) & RQUEUEMASK;
head = (head + 1) & RQUEUEMASK;
ch->ch_r_head = head & RQUEUEMASK;
head = ch->ch_r_head & RQUEUEMASK;
tail = ch->ch_r_tail & RQUEUEMASK;
qleft += RQUEUEMASK + 1;
head = (head + n) & RQUEUEMASK;
ch->ch_r_tail = tail = (tail + 1) & RQUEUEMASK;
head = (head + 1) & RQUEUEMASK;
ch->ch_r_head = head & RQUEUEMASK;
rmask = RQUEUEMASK;
qleft += RQUEUEMASK + 1;