s_mp_exch
void s_mp_exch(mp_int *a, mp_int *b); /* swap a and b in place */
s_mp_exch(pQ, q);
s_mp_exch(pR, r);
s_mp_exch(&x, b);
s_mp_exch(&s, c);
s_mp_exch(&s, c);
s_mp_exch(&f, &g);
s_mp_exch(c, &d);
s_mp_exch(mp1, mp2);
s_mp_exch(&tmp, a);
s_mp_exch(&tmp, b);
s_mp_exch(&tmp, b);
s_mp_exch(&qp, q);
s_mp_exch(&s, c);