def miller(P, Q, n, denominator=False):
# return the miller loop f_{P, n}(Q) for an even embedded degree curve
if Q.is_zero():
raise ValueError("Q must be nonzero.")
n = ZZ(n)
if n.is_zero():
raise ValueError("n must be nonzero.")
n_is_negative = False
if n < 0:
n = n.abs()
n_is_negative = True
t_num, t_den = 1, 1
V = P
S = 2 * V # V=P is in affine coordinates
nbin = n.bits()
i = n.nbits() - 2
while i > -1:
[S, [ell_num, ell_den]] = eval_line(V, V, Q)
t_num = (t_num**2) * ell_num
if denominator:
[R, [vee_num, vee_den]] = eval_line(S, -S, Q)
t_den = (t_den**2) * ell_den * vee_num
t_num *= vee_den
V = S
if nbin[i] == 1:
[S, [ell_num, ell_den]] = eval_line(V, P, Q)
t_num = t_num * ell_num
if denominator:
[R, [vee_num, vee_den]] = eval_line(S, -S, Q)
t_den *= ell_den * vee_num
t_num *= vee_den
V = S
i = i - 1
if not (denominator):
t_den = 1
if n_is_negative:
t_num, t_den = t_den, t_num
S = -S
return [S, [t_num, t_den]]
def decompose(P, f, g=None, target=None):
"""
Compute a polynomial Q of degree target such that compose(Q, f,
g). Assumes deg f >= deg g. The result is returned as a list of
coefficients.
"""
def dec(P, f, g, invf, invg):
a = f.parent()(0)
if P.degree() >= f.degree() + g.degree():
a, P = P.quo_rem(f)
return a + (P * invf) % g, (P * invg) % f
if g is None:
g = f.parent()(1)
if target is None:
target = ZZ(P.degree() // f.degree())
n, a, b = 0, 1, 1
moduli = []
for bit in reversed(target.bits()):
if bit:
n1, a1, b1 = n + 1, a * f, b * g
else:
n1, a1, b1 = n, a, b
moduli.append((n1, a1, b1))
n, a, b = n + n1, a * a1, b * b1
res = {0: P}
for n, a, b in reversed(moduli):
newres = {}
_, inva, invb = a.xgcd(b)
for i, p in res.iteritems():
p0, p1 = dec(p, a, b, inva, invb)
newres[i + n] = p0 + newres.get(i + n, 0)
newres[i] = p1 + newres.get(i, 0)
res = newres
return [res[i] for i in range(len(res))]
def decompose(P, f, g=None, target=None):
"""
Compute a polynomial Q of degree target such that compose(Q, f,
g). Assumes deg f >= deg g. The result is returned as a list of
coefficients.
"""
def dec(P, f, g, invf, invg):
a = f.parent()(0)
if P.degree() >= f.degree() + g.degree():
a, P = P.quo_rem(f)
return a + (P * invf) % g, (P * invg) % f
if g is None:
g = f.parent()(1)
if target is None:
target = ZZ(P.degree() // f.degree())
n, a, b = 0, 1, 1
moduli = []
for bit in reversed(target.bits()):
if bit:
n1, a1, b1 = n + 1, a * f, b * g
else:
n1, a1, b1 = n, a, b
moduli.append((n1, a1, b1))
n, a, b = n + n1, a * a1, b * b1
res = {0: P}
for n, a, b in reversed(moduli):
newres = {}
_, inva, invb = a.xgcd(b)
for i, p in res.iteritems():
p0, p1 = dec(p, a, b, inva, invb)
newres[i + n] = p0 + newres.get(i + n, 0)
newres[i] = p1 + newres.get(i, 0)
res = newres
return [res[i] for i in range(len(res))]
