// Enter with u and v in the most-significant three words of q0 and
// q1 respectively, and zero in the low words, and zero in q15; leave
// with z = u v in the high three words of q0, and /junk/ in the low
// Enter with u and v in the most-significant three words of q0 and
// q1 respectively, and zero in the low words, and zero in q15; leave
// with z = u v in the high three words of q0, and /junk/ in the low