source 1987 Montgomery "Speeding the Pollard and elliptic curve methods of factorization", page 261, fifth display compute X5 = Z1((X3-Z3)(X2+Z2)+(X3+Z3)(X2-Z2))^2 compute Z5 = X1((X3-Z3)(X2+Z2)-(X3+Z3)(X2-Z2))^2