source 2008.02.25 Hisil--Wong--Carter--Dawson compute SC1 = S1 C1 compute DZ1 = D1 Z1 compute E = DZ1^2 compute F = SC1^2 compute G = a F compute Z3 = E+G compute D3 = E-G compute CC1 = C1^2 compute C3 = 2(F+CC1^2)-Z3 compute S3 = (SC1+DZ1)^2-E-F