Asymmetric Arithmetic Rounding

Introduction

.NET rounding is limited to bankers rounding. I searched far and wide for an alternative. I didn't find one. There may be better ways to do this, but I believe this is pretty lightweight and simple.

The Scoop: 1 - 4: rounds down, 5 - 9: rounds up. Simply add these functions to a class or a form or whatever you are programming, and call them whenever you need to do rounding.

public static float aaRounding(float numToRound, int numOfDec)
{
    return (float)aaRounding((decimal)numToRound, numOfDec);
}

public static double aaRounding(double numToRound, int numOfDec)
{
    return (double)aaRounding((decimal)numToRound, numOfDec);
}
  
public static decimal aaRounding(decimal numToRound, int numOfDec)
{
    if (numOfDec < 0)
    {
        throw new ArgumentException("BetterMath.Rounding:" + 
              " Number of decimal places must be 0 or greater", 
              "numOfDec");
    }

    decimal num = numToRound;

    //Shift the decimal to the right the number 
    //of digits they want to round to
    for (int i = 1; i <= numOfDec; i++)
    {
        num *= 10;
    }

    //Add/Subtract .5 to TRY to increase the number 
    //that is to the LEFT of the decimal
    if (num < 0)
    {
        num -= .5M;
    }
    else
    {
        num += .5M;
    }

    //Cut off the decimal, you have your answer!
    num = (decimal)((int)num);

    //Shift the decimal back into its proper position
    for (int i = 1; i <= numOfDec; i++)
    {
        num /= 10;
    }

    return num;

}

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