Round () Rounding out the js Banker algorithm, round banker

Round () Rounding out the js Banker algorithm, round banker

First, let's guess the result returned by round (0.825, 2,

First, SQL server Returns 0.83

The returned result of js is 0.83. The code is as follows:

Var B = 0.825; alert (Math. round (B * 100)/100); in fact, the toFixed function can be directly used in js,

Var B = 0.825; alert (B. toFixed (2 ));

This also returns 0.83

 

However, C # returns 0.82

This is not our expectation of 0.83. Why? In fact, Math. Round () in C # does not use the "Rounding" method,Four Homes, six in five get even (Banker algorithm). If the number of digits to be rounded to is "less than 5" or "greater than 5", the result is rounded up to 5 in the general sense. if "5 is equal to the value after the number of digits to be rounded off", check whether the last digit is an even number or an odd number.

Math. round (1.25, 1) = 1.2 because the first part of 5 is 2, which is an even number, the 5 is rounded off without carrying Math. round (1.35, 1) = 1.4 because the first part of 5 is 3, which is an odd number, so carry.

To solve this problem, Microsoft provides other APIs

Round (Decimal, MidpointRounding)

Round (Double, MidpointRounding)

Round (Decimal, Int32, MidpointRounding)

Round (Double, Int32, MidpointRounding)

Some people on the Internet say that this API has a problem when calculating decimals. In fact, we can implement the Round function by ourselves,

 public static decimal Round(decimal d, int decimals)
        {
            decimal tenPow = Convert.ToDecimal(Math.Pow(10, decimals));
            decimal scrD = d * tenPow + 0.5m;
            return (Convert.ToDecimal(Math.Floor(Convert.ToDouble(scrD))) / tenPow);
        }  

Or,

 public static decimal Round(decimal d, int decimals)
        {
            d = d + 0.000000000000001m;
            return Decimal.Round(d, decimals);
        }

 

If we need to use js to implement the Banker algorithm, how can we implement it?

 Number.prototype.round = function (len)
        {
            var old = this;
            var a1 = Math.pow(10, len) * old;
            a1 = Math.round(a1);
            var oldstr=old.toString()
            var start = oldstr.indexOf(".");
            if (start > 0 &&  oldstr.split(".")[1].length==len+1)
            {
                if (oldstr.substr(start + len + 1, 1) == 5)
                {
                    var flagval = oldstr.substr(start + len, 1) - 0;
                    if (flagval % 2 == 0)
                    {
                        a1 = a1 - 1;
                    }
                }
            }
            var b1 = a1 / Math.pow(10, len);
            return b1;
        }