source 2007 Hisil--Carter--Dawson compute A = X1^2 compute B = Y1^2 compute C = Z1^2 compute D = A+B compute E = A+C compute F = B+C compute G = (X1+Y1)^2-D compute H = (X1+Z1)^2-E compute J = (Y1+Z1)^2-F compute X3 = (J-G)(H+2 E) compute Y3 = (G-H)(J+2 F) compute Z3 = (H-J)(G+2 D)