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)