m *Modulus) *Nat { overflow := x.add(y) x.maybeSubtractModulus(choice(overflow), m) return x } // montgomeryRepresenta calculates x = x * R mod m, with R = 2^(_W * n) and // n = len(m.nat.limbs). // // Faster Montgomery multiplication replaces standard modular multiplication for // numbers in this representation. // // This assumes that x is already reduced mod m. func (x *Nat) montgomeryRepresenta(m *Modulus) *Nat { // A Montgomery multiplication (which computes a * b / R) by R * R works out //...