,f);M(d,b,x);S(b,e);sel25519(a,b,r);sel25519(c,d,r);}FOR(i,16){x[i+16]=a[i];x[i+32]=c[i];x[i+48]=b[i];x[i+64]=d[i];}inv25519(x+32,x+32);M(x+