name twisted Edwards curves
parameter a
parameter d
coordinate x
coordinate y
satisfying a x^2+y^2 = 1+d x^2 y^2
addition x = (x1 y2+y1 x2)/(1+d x1 x2 y1 y2)
addition y = (y1 y2-a x1 x2)/(1-d x1 x2 y1 y2)
doubling x = (x1 y1+y1 x1)/(1+d x1 x1 y1 y1)
doubling y = (y1 y1-a x1 x1)/(1-d x1 x1 y1 y1)
negation x = -x1
negation y = y1
neutral x = 0
neutral y = 1
toweierstrass u = (1+y)/(1-y)
toweierstrass v = 2 (1+y)/(x(1-y))
a0 = 1/(a-d)
a1 = 0
a2 = 4 a/(a-d)-2
a3 = 0
a4 = 1
a6 = 0
fromweierstrass x = 2 u/v
fromweierstrass y = (u-1)/(u+1)