丸め処理 (小数点以下 n 位で丸める)

Rounding.vb

''' <summary>
''' 丸め
''' </summary>
''' <remarks>
''' 参考)
''' 　http://ja.wikipedia.org/wiki/%E7%AB%AF%E6%95%B0%E5%87%A6%E7%90%86#.E4.B8.B8.E3.82.81.E3.81.AE.E7.A8.AE.E9.A1.9E
''' 　http://rurema.clear-code.com/2.1.0/method/BigDecimal/s/mode.html
''' </remarks>
Public Class Rounding
    
    ''' <summary>
    ''' 切り上げ (指定値を下回らない最小値 / RM: Rounding toward Minus infinity)
    ''' </summary>
    Public Shared Function Ceiling(value As Double, digits As Integer)
        Dim shift = 10 ^ digits
        Return Math.Ceiling(value * shift) / shift
    End Function
 
    ''' <summary>
    ''' 切り捨て (指定値を上回らない最大値 / RP: Rounding toward Plus infinity)
    ''' </summary>
    Public Shared Function Floor(value As Double, digits As Integer)
        Dim shift = 10 ^ digits
        Return Math.Floor(value * shift) / shift
    End Function
 
    ''' <summary>
    ''' 切り捨て (0に近い側 / RZ: Rounding toward Zero)
    ''' </summary>
    Public Shared Function Down(value As Double, digits As Integer)
        Dim shift = 10 ^ digits
        Return Math.Truncate(value * shift) / shift
    End Function
 
    ''' <summary>
    ''' 切り上げ (0に遠い側 / RI: Rounding toward Infinity)
    ''' </summary>
    Public Shared Function Up(value As Double, digits As Integer)
        Dim shift = 10 ^ digits
        Dim v = value * shift
        Return If(v < 0, Math.Floor(v), Math.Ceiling(v)) / shift
    End Function
 
    ''' <summary>
    ''' 四捨五入 (R: Round)
    ''' </summary>
    Public Shared Function HalfUp(value As Double, digits As Integer)
        Return Math.Round(value, digits, MidpointRounding.AwayFromZero)
    End Function
 
    ''' <summary>
    ''' 偶数丸め (RN: Round to the Nearest even)
    ''' </summary>
    Public Shared Function HalfEven(value As Double, digits As Integer)
        Return Math.Round(value, digits)
    End Function
 
End Class