C# 高精度乘法 支持小数（待优化）

将N*N乘法转化为（N*n1）+(N*n2)....(N*nn)

乘完后在补充小数点

        public static char[] Quadrature(string a, string b)
        {
            char[] r = new char[1] { '0' };
            List<int> bu = new List<int>();
            List<int> au = new List<int>();
            int adot = a.Length;
            int bdot = b.Length;
            for (int i = b.Length - 1; i >= 0; i--)
            {
                if (b[i] == '.')
                {
                    bdot = i;
                }
                else
                {
                    bu.Add(b[i] - 48);
                }
            }
            for (int i = a.Length - 1; i >= 0; i--)
            {
                if (a[i] == '.')
                {
                    adot = i;
                }
                else
                {
                    au.Add(a[i] - 48);
                }
            }
            a = "";
            for (int i = au.Count() - 1; i >= 0; i--)
            {
                a += au[i];
            }

            for (int i = 0; i < bu.Count(); i++)
            {
                char[] qq = QuadUnit(a, bu[i]);
                string qqq = "";
                for (int j = 1; j < i + 1; j++)
                {
                    qqq = "";
                    foreach (var item in qq)
                    {
                        qqq += item;
                    }
                    qq = QuadUnit(qqq, 10);
                }
                qqq = "";
                foreach (var item in qq)
                {
                    qqq += item;
                }
                string rr = "";
                foreach (var item in r)
                {
                    rr += item;
                }
                r = SumF(rr, qqq);

            }
            List<char> rer = new List<char>();
            for (int i = 0; i < r.Count(); i++)
            {
                rer.Add(r[i]);
            }
            int con = rer.Count();
            int dot = a.Length + b.Length - (adot + bdot);

            //Console.WriteLine(a);
            //Console.WriteLine(b);
            //Console.WriteLine(a.Length);
            //Console.WriteLine(b.Length);
            //Console.WriteLine(adot);
            //Console.WriteLine(bdot);
            //Console.WriteLine(con);
            //Console.WriteLine(dot);
            //Console.WriteLine(con-dot);

            if (con - dot > 0)
            {
                if (con - dot != con)
                {
                    rer.Insert(con - dot + 1, '.');
                }
            }
            else if (con - dot < 0)
            {
                rer.Insert(0, '.');
                rer.Insert(0, '0');

                int co = -1 * (con - dot) - 1;
                while (co > 0)
                {
                    rer.Insert(2, '0');
                    co--;
                }
            }
            else
            {
                rer.Insert(0, '.');
                rer.Insert(0, '0');
            }

            return rer.ToArray();
        }
        public static char[] QuadUnit(string a, int b)
        {
            int r = 0;
            int jw = 0;
            char[] c = a.ToCharArray();
            List<char> items = new List<char>();
            List<char> ritems = new List<char>();
            for (int i = c.Count() - 1; i >= 0; i--)
            {
                if (a[i] == '.')
                {
                    r = '.';
                    items.Add(Convert.ToChar(r));
                }
                else
                {
                    r = ((int)c[i] - 48) * b + jw;
                    jw = 0;
                    if (r >= 10)
                    {
                        jw = r / 10;
                        r %= 10;
                    }
                    items.Add(Convert.ToChar(r.ToString()));
                }

            }
            if (jw > 0)
            {
                items.Add(Convert.ToChar(jw.ToString()));
            }

            for (int i = (items.Count() - 1); i >= 0; i--)
            {
                ritems.Add(items[i]);
            }
            return ritems.ToArray();
        }