将数字转换为数据大小形式

/// <summary>
        /// 将数字转换为数据大小格式
        /// </summary>
        /// <param name="bytes"></param>
        /// <returns></returns>
        public static string FormatBytesStr(long bytes)
        {
            double num;
            if (bytes > 0x40000000)
            {
                num = (double)bytes / 0x40000000;
                return (num.ToString("N02") + "G");
            }
            if (bytes > 0x100000)
            {
                num = (double)bytes / 0x100000;
                return (num.ToString("N02") + "M");
            }
            if (bytes > 0x400)
            {
                num = (double)bytes / 0x400;
                return (num.ToString("N02") + "K");
            }
            return (bytes.ToString() + "B");
        }

以b为单位