source 2007 Feng--Wu, second JQN2 doubling formula, plus epsilon=1, plus delta=-a, plus scaling, plus common-subexpression elimination appliesto 2xxyzz compute R1 = (X1+Z1)^2-XX1-ZZ1 compute Y12 = 2 Y1 compute T1 = R1^2 compute T12 = 2 T1 compute T2 = Y12^2 compute X3 = (R1+Y12)^2-T1-T2 compute XX3 = X3^2 compute Y3 = (T2+c T12)^2-c XX3 compute Z3 = T2-a T12-8 XX1^2 compute ZZ3 = Z3^2