c#实现四舍五入(Round)/向上舍入(RoundUp)/向下舍入(RoundDown)

dotnet的旧版框架的四舍五入和通常理解的四舍五入是不同的，以下的代码解决了这个问题

     
        // 四舍五入
        public static decimal Round(this decimal num, int decimals)
        {
            decimal precision = (decimal)Math.Pow(10.0, decimals + 1);

            return RoundDown(num + 5 * 1 / precision, decimals);

        }

        // 向上舍入
        public static decimal RoundUp(this decimal num, int decimals)
        {
            decimal precision = (decimal)Math.Pow(10.0, decimals);
            return RoundDown(num, decimals) + 1 / precision;

        }

   
        // 向下舍入
        public static decimal RoundDown(this decimal num, int decimals)
        {
            decimal precision = (decimal)Math.Pow(10.0, decimals);
            return ((int)(num * precision)) / precision;
        }

        // 四舍五入
        public static double Round(this double num, int decimals)
        {
            double precision = (double)Math.Pow(10.0, decimals + 1);

            return RoundDown(num + 5 * 1 / precision, decimals);

        }

        // 向上舍入
        public static double RoundUp(this double num, int decimals)
        {
            double precision = Math.Pow(10.0, decimals);
            return RoundDown(num, decimals) + 1 / precision;

        }

        // 向下舍入
        public static double RoundDown(this double num, int decimals)
        {
            double precision = (double)Math.Pow(10.0, decimals);
            return ((int)(num * precision)) / precision;
        }