QELEM
QELEM(q,i+1) = QELEM(q,i);
QELEM(q,after+1) = seqnum;
expected = (QELEM(q,q->start+q->length-1)+1) & q->mask;
if (after(QELEM(q,q->start), seqnum, q->mask)) {
if (seqnum == QELEM(q,q->start+q->length-1))
if (seqnum == QELEM(q,i))
if (after(seqnum, QELEM(q,i), q->mask) &&
after(QELEM(q,i+1), seqnum, q->mask)) {