C# 高精度加法 支持小数（待优化）

直接上代码

实现思路：

1、首先小数点补 位，9223372036854775808.9+9223372036854775808.9223372036854775808 => 9223372036854775808.900000000000000000+9223372036854775808.9223372036854775808

2、然后开始按位进行计算，进位数放入jw，在下一位计算时加上

   public static char[] Sum(string a, string b)
        {
            return Sum(a.ToCharArray(), b.ToCharArray());
        }
        public static char[] Sum(char[] a, char[] b)
        {
            char[] c = a;//补位后的a
            char[] d = b;//补位后的b
            int alength = a.Count();//a长度
            int blength = b.Count();//b长度
            int adot = alength;//a小数点位置
            int bdot = blength;//b小数点位置
            #region 小数点补位
            for (int i = 0; i < alength; i++)
            {
                if (a[i] == '.')
                {
                    adot = i;
                    break;
                }
            }
            for (int i = 0; i < blength; i++)
            {
                if (b[i] == '.')
                {
                    bdot = i;
                    break;
                }
            }
            if (adot != alength || bdot != blength)
            {
                if (adot == alength)
                {
                    c = new char[alength + 1 + blength - bdot - 1];
                    for (int i = 0; i < c.Length; i++)
                    {
                        if (i < alength)
                        {
                            c[i] = a[i];
                        }
                        else if (i == alength)
                        {
                            c[i] = '.';
                        }
                        else
                        {
                            c[i] = '0';
                        }
                    }

                }
                else if (bdot == blength)
                {
                    d = new char[blength + 1 + alength - adot - 1];
                    for (int i = 0; i < d.Length; i++)
                    {
                        if (i < blength)
                        {
                            d[i] = b[i];
                        }
                        else if (i == blength)
                        {
                            d[i] = '.';
                        }
                        else
                        {
                            d[i] = '0';
                        }
                    }
                }
                else
                {
                    if (alength - adot > blength - bdot)
                    {
                        d = new char[blength + ((alength - adot) - (blength - bdot))];
                        for (int i = 0; i < d.Length; i++)
                        {
                            if (i < blength)
                            {
                                d[i] = b[i];
                            }
                            else
                            {
                                d[i] = '0';
                            }
                        }
                    }
                    else
                    {
                        c = new char[alength + ((blength - bdot) - (alength - adot))];
                        for (int i = 0; i < c.Length; i++)
                        {
                            if (i < alength)
                            {
                                c[i] = a[i];
                            }
                            else
                            {
                                c[i] = '0';
                            }
                        }
                    }
                }
            }

            #endregion

            List<char> item = new List<char>();
            int cl = c.Length;
            int dl = d.Length;
            int r = 0;
            int jw = 0;//进位
            do
            {
                if (cl > 0 && dl > 0)
                {
                    if (c[cl - 1] == '.')
                    {
                        r = '.';
                    }
                    else
                    {
                        r = (int)c[cl - 1] + (int)d[dl - 1] - 96 + jw;
                        jw = 0;
                        if (r >= 10)
                        {
                            jw++;
                            r = r - 10;
                        }
                    }
                }
                else if (cl <= 0 && dl > 0)
                {
                    r = d[dl - 1] - 48+jw;
　　　　　　　　　　　 jw = 0;
                    if (r >= 10)
                    {
                        jw++;
                        r = r - 10;
                    }
                }
                else if (cl > 0 && dl <= 0)
                {
                    r = c[cl - 1] - 48+jw;
　　　　　　　　　　　 jw = 0;
                    if (r >= 10)
                    {
                        jw++;
                        r = r - 10;
                    }
                }

                if (r == 46)
                {
                    item.Add(Convert.ToChar(r));
                }
                else
                {
                    item.Add(Convert.ToChar(r.ToString()));
                }
                cl--; dl--;
            } while (cl > 0 || dl > 0);
            if (jw == 1)
            {
                item.Add('1');
            }
            return item.ToArray();
        }