source 1998 Cohen--Miyaji--Ono "Efficient elliptic curve exponentiation using mixed coordinates", formula (3), plus common-subexpression elimination compute Y1Z2 = Y1 Z2 compute X1Z2 = X1 Z2 compute Z1Z2 = Z1 Z2 compute u = Y2 Z1-Y1Z2 compute uu = u^2 compute v = X2 Z1-X1Z2 compute vv = v^2 compute vvv = v vv compute R = vv X1Z2 compute A = uu Z1Z2-vvv-2 R compute X3 = v A compute Y3 = u(R-A)-vvv Y1Z2 compute Z3 = vvv Z1Z2