def mod_sub(self, other, m):
""" Returns the difference of self and other modulo m.
Example:
>>> Bn(10).mod_sub(Bn(2), Bn(11))
Bn(8)
"""
r = Bn()
_C.bn_sub(r.bn, self.bn, other.bn)
_C.bn_mod(r.bn, r.bn, m.bn)
return r
def mod_mul(self, other, m):
""" Return the product of self and other modulo m.
Example:
>>> Bn(10).mod_mul(Bn(2), Bn(11))
Bn(9)
"""
r = Bn()
_C.bn_mul(r.bn, self.bn, other.bn)
_C.bn_mod(r.bn, r.bn, m.bn)
return r
def mod_add(self, other, m):
""" Returns the sum of self and other modulo m.
Example:
>>> Bn(10).mod_add(2, 11)
Bn(1)
>>> Bn(10).mod_add(Bn(2), Bn(11))
Bn(1)
"""
r = Bn()
_C.bn_add(r.bn, self.bn, other.bn)
_C.bn_mod(r.bn, r.bn, m.bn)
return r
def mod_inverse(self, m):
""" Compute the inverse mod m, such that self * res == 1 mod m.
Example:
>>> Bn(10).mod_inverse(m = Bn(11))
Bn(10)
>>> Bn(10).mod_mul(Bn(10), m = Bn(11)) == Bn(1)
True
"""
gcd = Bn()
inv = Bn()
_C.bn_gcd_ext(gcd.bn, inv.bn, _FFI.NULL, self.bn, m.bn)
_C.bn_mod(inv.bn, inv.bn, m.bn)
if gcd != Bn(1):
raise Exception("No inverse for ", self, "modulo ", m)
return inv
def __mod__(self, other):
rem = Bn()
_C.bn_mod(rem.bn, self.bn, other.bn)
return rem