source 2007 Feng--Wu, first JQN2 doubling formula, plus correction of obvious typos, plus epsilon=1, plus delta=-a, plus scaling, plus common-subexpression elimination
compute R1 = (X1+Z1)^2-XX1-ZZ1
compute A1 = (R1+2 Y1)^2
compute A2 = 4 Y1^2
compute Q1 = XX1^2
compute S1 = R1^2
compute S12 = 2 S1
compute M = a S12
compute A2M = A2-M
compute X3 = A1-A2-S1
compute Y3 = A2M(A2+M)+S12^2
compute Z3 = A2M-8 Q1
compute XX3 = X3^2
compute ZZ3 = Z3^2