def _fib_res(self, n, p):
""" fibonacci sequence nth item modulo p """
if n == 0:
return (0, 1)
a, b = self._fib_res(n >> 1, p)
c = mod((mod(a, p) * mod(((b << 1) - a), p)), p)
d = mod((powmod(a, 2, p) + powmod(b, 2, p)), p)
if n & 1 == 0:
return (c, d)
return (d, mod((c + d), p))
def get_n_mod_d(self, n, d, use="mersenne"):
if n < 0:
ValueError("Negative arguments not implemented")
if use == "gmpy":
return mod(fib(n), d)
elif use == "mersenne":
return powmod(2, n, d) - 1
else:
return self._fib_res(n, d)[0]