base62与long的相互转换

public static class Converter
    {
        private static String keys = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";//编码,可加一些字符也可以实现72,96等任意进制转换，但是有符号数据不直观，会影响阅读。
        private static int exponent = keys.Length;//幂数

        /// <summary>
        /// decimal value type to 62 string
        /// </summary>
        /// <param name="value">The max value can not more decimal.MaxValue<</param>
        /// <returns>Return a specified 62 encode string</returns>
        public static string ToBase62(this long value)//17223472558080896352ul
        {
            string result = string.Empty;
            do
            {
                var index = value % exponent;
                result = keys[(int)index] + result;
                value = (value - index) / exponent;
            }
            while (value > 0);

            return result;
        }


        /// <summary>
        /// 62 encode string to decimal
        /// </summary>
        /// <param name="value">62 encode string</param>
        /// <returns>Return a specified decimal number that decode by 62 string</returns>
        public static long FromBase62(this string value)//bUI6zOLZTrj
        {
            long result = 0;
            for (int i = 0; i < value.Length; i++)
            {
                int x = value.Length - i - 1;
                result += keys.IndexOf(value[i]) * Pow(exponent, x);// Math.Pow(exponent, x);
            }
            return result;
        }

        /// <summary>
        /// 一个数据的N次方
        /// </summary>
        /// <param name="x"></param>
        /// <returns></returns>
        private static long Pow(long baseNo, long x)
        {
            long value = 1;////1 will be the result for any number's power 0.任何数的0次方，结果都等于1
            while (x > 0)
            {
                value = value * baseNo;
                x--;
            }
            return value;
        }
    }

https://www.cnblogs.com/Jeremys/p/3796466.html