Example #1
0
        private static BigInteger ReduceBarrett(BigInteger x, BigInteger m, BigInteger mr, BigInteger yu)
        {
            int xLen = x.BitLength, mLen = m.BitLength;
            if (xLen < mLen)
                return x;

            if (xLen - mLen > 1)
            {
                int k = m.magnitude.Length;

                BigInteger q1 = x.DivideWords(k - 1);
                BigInteger q2 = q1.Multiply(yu); // TODO Only need partial multiplication here
                BigInteger q3 = q2.DivideWords(k + 1);

                BigInteger r1 = x.RemainderWords(k + 1);
                BigInteger r2 = q3.Multiply(m); // TODO Only need partial multiplication here
                BigInteger r3 = r2.RemainderWords(k + 1);

                x = r1.Subtract(r3);
                if (x.sign < 0)
                {
                    x = x.Add(mr);
                }
            }

            while (x.CompareTo(m) >= 0)
            {
                x = x.Subtract(m);
            }

            return x;
        }