mvl = m->v + k + 1;
r = mp_new(k + 1, (q->f | mb->m->f) & MP_BURN);
mpx_umul(r->v, r->vl, q->v + k + 1, q->vl, mb->m->v, mb->m->vl);
mvl = m->v + k + 1;
r = mp_new(k + 1, (q->f | mb->m->f) & MP_BURN);
mpx_umul(r->v, r->vl, q->v + k + 1, q->vl, mb->m->v, mb->m->vl);